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everybody, to Wednesday Nite >> Tom Zinnen: Welcome,
I'm Tom Zinnen. I work here at the
UW Biotechnology Center and I also work at the UW Extension
Cooperative Extension.
Wisconsin Alumni Association, Othe PLATO Lifelong Learninghe
Group, and Wisconsin Public Television, thanks to coming to
Wednesday Nite at the Lab.
night, 50 times a year. Tonight I'm delighted to be able
to introduce to you Professor Rich Hartel of the Department of
Food Science here at UW-Madison.
and tempering of chocolate. It flows and blooms as it grows,
as I like to put it.
New York, but I was rather He was born in Brooklyn,
told me that because he doesn't sound like he's from Brooklyn.
He went to school at upstate
been here a long time. New York at Potsdam, and he's
pleasures to get to work with It'him over the years.reat
He's done science expeditions,
Lab at least four or five times, he's done Wednesday Nite at the
experimental samples. and the be[LAUGHTER] he brings
So please join me in welcoming
at the Lab. Rich Harte[APPLAUSE]sday Nite
Rich Hartel: Well, it's good
I remember it was three years ago and I remember that night
because we were over in the other room and I think you were
sitting at my feet and there
So seriously when I wanted to whand out samples I just had to.
do this and give the sample.
I, at that point, didn't know how many sample bags to prepare,
so I'm afraid I was a little
Hopefully I got enough this short on time.of those.
So how many were at that talk?
So I recognize several of the That wafaces here.rs ago.
And so it's for you that I changed everything.
[LAUGHTER]
that talk. So I'm not going to re-do
different direction, so I call I've decided to go in a
But as with any class you always it 202 instead of 101.
what you've done before to bring go back a little bit and cover
So that's what I'm going to do. I'm going to start out with some
of the same things that we
Primarily, where does chocolate come from and how is it made.
And then we're going to get to a
properties that chocolate pexhibits, things that we wantof
from them, and in previous talks
polyphenols, that kind of stuff, I've covered flavor and
on the rheology of melted chocolate because that's a verys
important aspect and you have some samples there that I'm
going to walk you through what
We've got to explain a little tbit of rheology but eventually
we'll get to a map and I'll put different chocolates on that map
and you'll understand when we get there.
And then another aspect of
is if you just take melted chocolate that's fairly unique
get something that you don't chocolate and cool it down, you
It blooms. want to look at again.
butter and its crystallization So we have to control the cocoa
I'm going to talk about that, and I've got some really cool
videos that we take in our lab
cocoa butter and how it acrystallizes and stuff likeut
that. And I'll wind up with bloom,
although I think I'll leave that
So that's the plan for today. And so the introduction part,
where does chocolate come from? It grows on trees.
So there's a friend of mine who is down in the plantations, the
cocoa plantations down near the equatorial range, and these pods
grow on trees and then they're
removed from the inside. harvested and the beans are
that in more detail. I'll show some more pictures of
and then they're shipped to wherever the chocolate is going
to be made. Where we get cocoa beans these
days from, there's three main sources.
There's west Africa.
become the standard for cocoa So Ibeans these days.rt of
Indonesia and Malaysia are
They tend to make a very trying to build their program.
a hard butter, but they're different type of cocoa butter,
And Brazil used to be the number trying to build their growth.
witches' broom kind of wiped out one producing country until
They're trying to make a the trees.
general trying to make a comeback, South America in
things. So that's where chocolate or
cacao comes from. Here's some, I'll show you some
pictures of these.
Sorry, these are the cocoa pods. Here's some cocoa beans.
not my pointer. So here's the cocoa pods growing
on trees. They grow out the side of the
trees.
this nice color. When they get ripe, they turn
by hand. And then they're harvested still
separating the pods from the So this is a physical process
The pods are cut open. trees.
choice here. Usually a machete is the tool of
And you can see here there's And inside is the cocoa beans.
sticking out, and there's on the half a pod with the beans
here. It's contained in this white
mucilaginous mass, which just means a bunch of sugars that
hold it all together that provide the growth medium for
the seeds as they sprout to create new cacao trees.
They scoop those out, put them
Sometimes it's in a rack like inthis.le.
This pile is a fermentation pile.
So the natural enzymes and
area start breaking down that mmucilaginous, the mass, thee
sugars there, and actually stops
So that's one of the things that the seeds from sprouting.
And the fermentation step is happens.
chocolate flavor are developed. So if you don't ferment the
cocoa beans and then try and do all the roasting and stuff like
that, it doesn't give the chocolate flavor.
So the fermentation process breaks down some of the more
complex chemicals that are in the cocoa beans into smaller and
smaller things like smaller proteins and smaller sugars that
then can participate in the Maillard browning reaction that
happens during roasting.
create the flavors, although the So it's an important process to
themselves. It's the precursors that are
created.
fermentation, then the cocoa So after four or five days of
set out to dry. bSo we bring the water contente,
down to something like a couple percent.
Remember this is done in
a state of life, I think. tSo this particular plantationis
has their beans on trucks or
roof there when it starts to racks and they go underneath the
and dry. rain, otherwise they come out
water content down to a couple And the principle is to get the
convert it into chocolate. percent so that we can then
comes from the cacao plantation So that we're going to use inat
making chocolate is the cocoa bean.
And this is what a bean looks like in large size.
So it's on the order of a quarter in size.
And, again, there's about 25-35 in each of the pods.
So it takes quite a few pods to make a big bar of chocolate.
So this is what would be
Cocoa in Milwaukee, the old Ambrosia Chocolate Company, that
would turn this into chocolate. And the process for making
chocolate is take the cocoa beans, so once it comes off the
plantation we call it cocoa bean, before that it's cacao.
So there's a fuzzy definition or
So we take those cocoa beans. fThat contains the shells.e.
And so these shells are separated off.
Sometimes it happens before roasting, sometimes it happens
after roasting, but what we're
nibs are again the roasted cocoa after are these nibs and these
flavor. So this is the material that has
the smell and the flavor and
chocolate. taste that we think of with
nibs and ground them down into But if we just took those cocoa
make a good chocolate bar out of chocolate liquor, we couldn't
Well I take that back, we could take a really good chocolate bar
out of that but it costs too
Most of us wouldn't pay for it. So what we do is take some of
the cocoa beans after they're ground up, take some of that
chocolate liquor and press out
And then we're going to add some the cocoa butter.
chocolate liquor to give us the of right fat content which isthe
really what governs the viscosity of the melted
chocolate.
specified by a viscosity. ASo it's a very important
attribute of chocolate, both
chocolate and sells it to a user, as well as the user who is
going to try and put it into
eat. something that we would buy and
separation is cocoa powder. TThis is an important thing ifn
you're making Oreo cookies or something like that.
So one of the important ingredients for Oreo cookies.
But the two things that we need to make chocolate are chocolate
liquor, which is just ground up cocoa beans, and cocoa butter.
So ground up cocoa beans, we
There really is no alcohol, although there is an ethanol
step in the fermentation
But it goes to ethanol and it quickly goes to acidic acid.
So there's no ethanol left in the chocolate liquor, but we
still call it chocolate liquor. And so it's basically ground up
cocoa beans.
fat to 55% average fat content It has anywhere from 48% to 57%
It's got a few percent water, so for cocoa beans.
there. a couple percent water that's in
solids and that's made up of And then the rest of it is cocoa
things like that. So that's what cocoa powder is,
is all the non-cocoa butter stuff and non-water stuff.
So cocoa powder is all of this
What makes chocolate unique are cocoathese alkaloids.rial.
And some people talk about
I had somebody ask me about would it be worthwhile to
decaffeinate cocoa beans. And I scratched my head and said
I'm not sure why because of the alkaloids in there, that's the
really, really minor one. And so the theobromine, and
actually the name for cacao is
on the presence of this alkaloid theobroma cacao and that's based
And that's the one that gives us, so if you were here for my
first talk that's the one that
happiness. gives the pleasant feeling of
chocolate is pleasurable to eat. It's part of why people think
And that's actually a physical It gives a good feeling.
like caffeine is. So if you think you're addictede
to chocolate, that's up here. [LAUGHTER]
So that's chocolate liquor. Again, we're going to use that
as the base for making
So to the chocolate liquor here we're going to add sucrose.
So this is just table sugar that's going to sweeten it.
Bulk it up a little bit.
we're making a milk chocolate. We might add milk powder if
is dark chocolates. MAnd then we would mix theseay
together. The sugar is in the form of
table sugar so you know that
You wouldn't want to put that in it's pretty coarse.
So we have to grind it down to a your mouth, it feels like sand.
size. sThat's where this refininge
operation is, and that's done by
through a series of rollers and the rollers, so there's a series
of gaps between five rollers and
size as it passes through to go eacfrom, say, 200 microns, in
initially, down to 25 microns at
So that's the refining process. Then it goes into a big mixing
tank, a big sheering vessel called the conch.
And that serves several purposes
flavors, it helps break any aggregates of the particles that
are reformed during the refining
And this is where we add the operation.
this is where we add lecithin as extra cocoa butter, and then
So when you look at the ingredients of a chocolate bar,
usually it says sugar, chocolate
and maybe some flavor like liquor, cocoa butter, lecithin,
So that's the smoothing out part vanilla, something like that.
And then we have melted of chocolate.s.
So for many companies then that chocolate, it's in molten form.
The conch is at high enough temperature that the cocoa
butter is melted. It goes into a tank farm.
So many companies have these big
melted chocolate and they even tanks, thousands of gallons of
have a room where it's 105 keep the room, at ADM Cocoa they
That's above the melting point degrees.
don't have to heat the tank, of cocoa butter, and so they
is a nice place in the they just heat the room, which
summertime. wiBut it keeps the chocolatehe
melted, and then it would be
they were going to use it for. offered whatever application
melted chocolate in tanker Some companies actually ship
So if you can imagine these big tanker, like a milk truck, going
down the road but it's insulated
How about that for an accident? and contai[LAUGHTER]chocolate.
Everybody would be looking
Better than molasses. >> Yeah, better than molasses,
right.
manufacturing process of So that's the end point of the
So if a company like ADM Cocoa manufacturing chocolate.
company like General Mills, then is selling chocolate to a
of melted chocolate. they may send them tanker trucks
chocolate into bars. They may actually form the
bars of chocolate. So we sometimes get 10-pound
have. That's a r[LAUGHTER] thing to
I actually have one that says world's largest chocolate bar.
[LAUGHTER]
in the form of wafers. Sometimes they distribute it
bars or wafers, that's usually Sometimes they make, it's mostly
chocolate. what is sent or the melted
into a molded bar, we have to But in ordtemper it.chocolate
So let's work on the liquid chocolate first.
So we'll go to--
to taste the chocolate liquor. Wait a minute, you're supposed
You have a bag in your bag that says CL on it for chocolate
liquor. If you've never tasted chocolate
liquor before, take a nibble of it.
Do you have any left? >> Tom, is there an extra bag
here? I'll give you mine.
Do you have an extra bag? Great.
So this is chocolate liquor.
What does it taste like? It's just ground up cocoa beans.
This is also called baking Bitter is the key word.
So it's unsweetened baking chocolate.
And that's the base from which chocolate.
look at different calibers of chocolates, the amount of the
chocolate liquor that's in there
quality of that chocolate. usually correlates with the
70% cacao chocolate, So if you're buying a Lindt,
We'll talk about that and we'll it'taste that here in just abar.
second. A less expensive chocolate may
only have 15% to 20% of that
provide some flavor, and then there's a lot of sugar to
provide bulking.
liquor. It's got about 50% fat and then
all of other what is really cocoa powder mixed in with the
cocoa butter. Okay?
Sorry I skipped over the first
But that leads us right to the taste.
of several different dark next one chocolates.comparison
And so you have, what do we have
You have two bags. here?
One's got a double set of disks. Neither of them are labeled.
what's used to ship chocolate Soaround from a supplier to ames
manufacturer. You have a half of square of
Lindt and you have, I thought we'd try something a little bit
different, a dark chocolate Hershey Kiss.
So these have very different
The Hershey dark, which is qualities of chocolate.
picked out some generic, I have boxes of chocolate in my lab so
I just picked out a few things
And this is a low to medium thatquality chocolate.nd.
And then, of course, the Lindt
chocolate with 70% cacao. Which means that it's got 70%
chocolate liquor. Because it's got 70% chocolate
liquor, it's got plenty of fat. Even if there's 50% fat in the
cocoa butter, then that chocolate has 35% fat.
And typically we're looking for between 28% and 35% fat to give
us the right rheological
flow of the melted chocolate. pSo it's got a little bit lessht
sugar than the Hershey dark.
cocoa butter because it's got It doesn't henough.add any extra
They both have lecithin and vanilla as a flavoring.
In the minimum semisweet, which is probably more like the disks.
I really don't even know what the Hershey's Dark Kiss is like
because that's a fairly new product, but these disks have
probably the minimum amount of
can get by with. cocoa chocolate liquor that they
I think I misspoke before, but And 35% is about the lowest you,
to go to still give a good that's about the lowest you want
But because that's 35% chocolate chocolate taste.
that's only 12.5% fat. liquor, half of it is fat,
us the rheological flow Thproperties that we want inve
melted chocolate so we've got to
And that was when the start of add 14% cocoa butter.
about was when people realized chocolate manufacture came
chocolate if we separate the that we can make a good eating
liquor and add it back and make cocoa ba good chocolate.ocolate
So what do you think of these disks?
And let's do it in comparison to
Chocolate flavor? The Lindt has more.
And that's a pretty obvious distinction.
Sweetness?
more sweetness. Again, 20% more sugar in there.
Some chocolates have maybe as high as 60% sugar.
So one of my friends at ADM calls it bunny chocolate.
So buy the cheapest bunny that
real chocolate. yAnd that's probably got a much
lower chocolate liquor content. So he calls that bunny
chocolate, and it's pretty
What he says is that if the bunny doesn't sell--
No, what he says is if the Santa
they just melt it back down dand make bunnies out of it.e,
[LAUGHTER]
in chocolate flavor, So very distinct difference
And again it comes from the amount of chocolate, primarily
comes from the amount of
products. chSo let me get your sense.wo
Where does the Hershey's Kiss fall?
Is it between those two or on one end or the other?
This is the sweeter of them?
The chocolate taste? Sweeter?
good as the disk? Better tSo it's a mix.r not as
Some people say better, some
So, again, I don't know off hand people say not so much.
Hershey's Kiss is. what the composition of this
Hershey's Bittersweet Special Dark, which I think is actually
this composition. So very different flavor based
on how much chocolate liquor is there.
But that's where we've been before is comparing these
tastes. Now I want to talk about what's
different between these in terms
So let's turn to the first topic of their rheology.
melted chocolate flow? that we have is how does the
picture here is melted chocolate So to think about that, the top
So here's all the particles. in my cartoonish sort of way.
cocoa powder particles. The sharper brown/black ones are
the sugar particles.
chocolate through the refining And so when we send that
particles down and down into operation, we're breaking those
on the average of 20 to 25 smaller and smaller size they're
A really good chocolate would be microns or so in size.
size. dA much coarser chocolate would
be closer to 30 microns.
those particles, which And so in the melted chocolate
and 70% of the mass of that melted chocolate, so if you took
any of these chocolates that you
mouth, what you would have is jtwo-thirds of it in particles,r
sugar and cocoa solids, and the rest of it is the liquid cocoa
butter. So the liquid cocoa butter,
we've all seen liquid fats, you just pour them out of container
and they flow really nicely.
those particles it's like taking But if you pack them with all
easily and packing it with sand water tor corn starch.r really
You ever try that?
And pack it with that many That's a weird one.
In fact, if you packed water particles.
really weird texture, really with corn starch, you'd get a
different rheological properties weird consistency and very
It's a different beast all by thanitself.ate.
But if you pack the water with
well it's not going to go sand and tanywhere.nd pour it,
Maybe not.
there is, how big the sand It depends on how much water
If you packed the water with 50% particles are.
pour it. sand particles, maybe you could
would pour a little bit. It would be like quick sand, it
properties. So the more and more particles
we pack into this liquid, the more and more solid like it
gets. And that's what we're dealing
with chocolate is a liquid, melted fat with these particles,
cocoa butter and sugar
close proximity. particles, packed in a fairly
size, 60% of the mass is that then we must have bazillions of
particles in there. And as you can imagine if you
try and pour that, those
across each other to get out of parthe cup and have a veryroll
different flow property,
oil itself. rheolThe water in there isliquid
particularly dangerous because
hydrophilic, it is water, but twhat part of chocolate isis
hydrophilic?
So if you're a water molecule in Well the sugar particles.
the sugar crystal surface there chocoland hang out there.ight to
That's why the lecithin is
The lecithin is a surfactant or an emulsifier, and it has both
hydrophobic and hydrophilic groups.
The hydrophilic group sits on the surface of the sugar
particle, where the water is, with the alkyl chains, the
hydrophobic part, that stick out
And it's actually those lecithin into the liquid fat.
particles to flow across each molecules thother.ow the sugar
Because if you're two hydrophilic surfaces in a
hydrophobic space, you go like
You stick together and you don't this.
And that's what happens when you move.
chocolate. add a little bit of water to
I was going to answer a little It turns into Tom's concrete.
happens when you add a little bit of water to chocolate is it
turns into concrete because the surface of the sugar crystals
becomes syrupy, and then when those particles try and move
past each other they just stick together and forms concrete.
That's what it is.
of those particles play an So obviously the characteristics
to flow, how easy it is to pump the chocolate and what its flows
properties are for specific applications.
Of course, when we solidify the cocoa butter, we get all of
these little cocoa butter crystals in there.
And that's a very important aspect of creating a nice
looking chocolate is to get just
polymorph of those cocoa butter the rightcrystals.d size and
So we'll go there next after we talk about rheology.
So here's, I like this picture, it's a three-phase contrast
image from a confocal microscope
a colleague of mine in Ireland. And this is one that has, it's a
milk chocolate. So it's got, the green particles
in there are milk powder. The sharper black ones, like
this one here, is a sugar particle that's been ground down
into a sharper space. There are some other brown ones
or green ones or black ones that
cocoa powder particles that have look round that are properly the
step too. But this is really cool becauseg
you can see very clearly how
So, again, the surrounding dense those particles are.
liquid cocoa butter. matrix, the blue part, is the
or a beaker and pouring it or trying to fill a mold with that
chocolate.
going to influence how that system flows and are going havee
a fairly large impact on the
So I talk about rheology like it's something everybody
understands.
little bit what viscosity and Let me rheology mean.plain a
So it's the science of the flow of fluids.
One way to look at it.
That's what it looks like when Here's melted chocolate.
my melting tank. you pour it from my beaker into
is the resistance of a material One way to tto flow.ut viscosity
So thick things when you try to pour them out of a cup take a
long time to flow or they don't flow.
Really thick things will stay there.
Water is something that has a low viscosity so it pours out
really quickly. Corn syrup, which is made up of
starch molecules that have been broken down, so corn syrup is a
sweetener made from starch but
glucose polymers that come from broken instarch.e various
But different corn syrups have
And the higher the chain length of the glucose polymer, the more
viscous the material is, not
So corn syrup, something that when you pour it takes a while
to come out and flow. So for us it's important because
we want to know how easy it is
example, or pump it from here to to pour into a mold, for
tanks where we're holding our chocolate to where we're going
to turn it into a disk or a molded piece.
We often have candy bars that have chocolate layers on it, and
that's actually a function of the rheology of the chocolate.
I'll come back to that in a minute.
And that actually has some
In chocolate there's a impact in how we swallow it.
that are going on from the combination of all the things
dissolving things with your saliva to sliding it down your
throat. Actually I was giving this talk
with a bunch of speech
or swallowing problems, and so I pathologists who study dysphagia
rheology with dysphagic fluids. wa( chuckles ) chocolate
But the bottom line is if you make chocolate and sell it to a
user, a manufacturer of a candy bar or something like that, then
they specify what their rheology properties are for that
chocolate based on what the application is going to be.
So in every lot of chocolate
in a tanker truck or in wafers, ththere's a specification that's
includes viscosity. So it's really, really critical
to both user and manufacturer to
g[INAUDIBLE].
No, I don't think so. But I don't know enough about
that to say for real. So what's the root of the word
rheology? I don't know that.
So we break rheological fluids, we break fluids into two
rheological classes.
but we can break them down into Actually theretwo.ore than this,
There's things that their flow
how fast you pour or how fast propertiesyou stir.n't matter
Water is that way.
it always looks like water. NoIt always feels like water.t,
It always reacts to your spoon
And so these things, water, oil, with the same force.
are basically Newtonian fluids, cand that means that there's ak
direct correlation between shear
profile, and the shear stress, rate, which is the velocity
applied to generate that which is the force that's
So a linear relationship that gives us Newtonian fluids, we're
not interested in those because chocolate fits in the
non-Newtonian shear thinning
So before I go there, let's talk fluid.
about that shear thickening
packing water with 60%-70% So remember I talked about
What happens is it becomes starch.
So everybody go home and do this shear thickening.
Don't blame me. [LAUGHTER]
But go home and do this if you
Take corn starch, approximately 70% corn starch, 30% water,
mix them together,
Like take it out and roll it in your hands, and because it's
shear thickening, when you roll it, you're applying a force,
and it acts like a solid. So you roll it in a ball.
You can roll that stuff in a
rolling it, it flows. ballIt's shear thickening.top
The faster you stir it, the thicker it appears.
And as soon as you stop stirring
That's a shear thickening fluid. it, it turns into a liquid.
It's cool. Seriously try it at home.
But that's not what we're It makes dealing with.at's okay.
So chocolate is a shear thinning
It's the type of material, just like ketchup, the more you stir
it, the thinner it appears. So there's many fluid foods
like this that have that
Even blood has that characteristic.
Toothpaste, think of toothpaste.
You apply a force. It sits in the tube.
out because applying that force Treduces its apparent viscosity
so it can flow out. But as soon as you stop, it
holds it shape, mostly it holds it shape as a cylinder.
So it reacts to force and flows but as soon as you stop applying
a force it stops flowing. So that's a shear thinning type
of fluid. You apply force, it looks
thinner, it can flow. When you stop applying the
force, it looks thicker again.
Varibar, that's the fluid that Ketchup is exactly the same way.
patients, people with swallowing people use to test dysphagic
So they have these kinds of things, so my colleague over in
the medical school here has that.
And we did a Wednesday Nite at
too. the Lab together a while back
chocolate pudding drink, If you remember tasting that
So chocolate fits in this shear thinning type of behavior.
Which means that the more you stir it, the faster you stir it,
the thinner it appears, the less
That's a pretty cool property. viscous it gets.
that here. And so we're going to play on
Well fat content is number one, but the particle structure,?
particle shape, and the effect
moisture or surfactants, also of the saffect that.her it's
So as a chocolate manufacturer, I have several things in my tool
bag that I can use to change the
Mostly they relate to how much rheological properties.
to how fine I grind those faparticles, how I grind thosee
particles, and then what type of
moisture content I leave in my surfactants I have, what type of
So all of those things are chocolate.
I can play with. things that, as a manufacturer,
So now I've got to talk a little Number one the fat content.
This is rheology 101. When we talk about shear
thinning fluids, we have three
in. facAnd so again we have theed
relationship between shear
And these are important because chocolate fits this model, and
so we need to understand these
of these parameters that tell us because I'm going to draw a map
that you're going to eat here. something about the chocolates
shear stress, so it's a force per unit area, to make the fluid
flow. That flow can be characterized
by a shear rate.
stir it at a certain shear rate Oand the chocolate applies awe
force back on our stirring
So that's one way to say it. mechanism.
shearing strain, or shear rate, and the stress is governed by a
relationship that's like this.
coefficient, K. If this is a Newtonian fluid,
this K would just be the
the fluid with. vHere this N value is a sheare
thinning index. It tells you how strongly shear
thinning that fluid is. So if N is one, it's a Newtonian
fluid, then you have a linear relationship between shear
stress and shear strain.
more shear thinning it is Tmeaning the more you stir it,e
the lower the viscosity seems to
And then there's this third parameter called the yield
stress which I like to use mash potatoes as my example of that.
So you've all had mashed
stress. pThose are the one that is youd
scoop it up and a mound stays on
That's because the yield stress, your spoon, it doesn't anywhere.
that material move, is larger tthan the force of gravity.s
So the force of gravity is not
We've had other mash potatoes where maybe we've added a little
too much water to the powder mix
turns into this gooey oconsistency and you pick it up
on the spoon and it runs off. Low yield stress.
So the force of gravity is
So yield stress, while some epeople, the rheologists, argue
what that really means, for us
potato, mashed potato, stand up whaon the spoon or not.hat
What it means for chocolate is
conveyor, does it stay up or when I put a dollop on to a
I'll get to where you think I'm going here in just a second.
Okay, so those are the three
in shear thinning behavior. paIt turns out it's even moreted
simple for chocolate because we use this model.
It's a slightly different model but similar.
And so we only have two, and I
I'm not sorry. didn't change that equation.
It's the same one. I meant to change that equation.
like, so sigma to the one half, sigma zero to the one half, K
gamma dot to the one half.
half. We take out of the N value and
we're left with two parameters. The yield stress, sigma zero,
similar to this, it's a similar principle as before.
And then the plastic viscosity
similar to that. or consistency coefficient is
each of those terms up to the one half to make the model thatt
works for chocolate.
rheology. For whatever reason that's what
chocolate people have grabbed onto as the constitutive
equation that describes chocolate rheology.
Whether it's fundamental or not,
everybody uses. And so what we're going to do is
take the two parameters, the
much force it takes to make the fluid to start flowing, against
the plastic viscosity.
different types of chocolates And that have very differenthree
characteristics.
determine the application of So it's the combination that
So a chocolate supplier doesn't just get viscosity, they get
these two parameters and they sell those chocolates based on
those parameters. So let's look at the Hershey's
Kiss. And you have a regular Hershey's
Kiss now in milk chocolate. And you never have to eat
anything in my classes but I
explore it, which means apoke at it and look at it.
Smell it, eat it. >> If you're not going to eat
yours...
So look at this cone of >> chocolate, right.ing.
Hershey's Kisses are made by
and putting a dollop on a simply takconveyor.d chocolate
So drop a dollop of chocolate onto a conveyor and this is what
you get.
nozzles dropping a dollop of So you can see the depositor
There's a whole row of, it's chocolate onto a conveyor.
these Hershey's Kisses or pretty ichocolate chips. all of
Chocolate chips are made in exactly the same way with
exactly the same properties.
have the right rheological So that chocolate, if it didn't
puddle. That's kind of like where those
wafers were going.
So this has a slightly lower Imagine that.
Hershey's Kiss so it flows more. rheological requirement than the
lower, rheologically, it would And if we were to make it even
[INAUDIBLE] j>> Temperature dependent,e.
but we're going to talk about temperature because we
have to have the cocoa butter melted which means it has to be
on the order of 35C.
below that to get the chocolate And wcocoa butter tempered.down
So this is done at about 35C. And this is tempered chocolate
being deposited onto the
So if we didn't want the depositing conveyor.
rheological characteristic would chocolate to flow off, what
We would want it to have a high wyield stress.t?
So we want it to have a high
drops, it stops flowing right yield valueaway.hat when it
We stop applying a force, it
shape. stops flowing and just holds its
at the start, that's what gives a flat bottom, but then it stops
flowing.
high viscosity. WSo viscosity and yield stressly
are slightly different things even though we just look at
melted chocolate and it looks like it's thick or thin.
But really there's those two
us. How much force it takes to makeo
it move, that's the yield value,
thick is it, and that's the and thplastic viscosity.g, how
And so to make a chocolate Kiss or a cookie drop, a chocolate
chip, or a wafer that has some
want to have chocolate that's got a high yield value, high
plastic viscosity.
with the variables that we can What do you think we might do
Lower the fat content. control to get that?
do it. That's usually the way that we
thicker, builds up the yield Lower the fat content makes it
particles can't flow across each stress because now those
So it builds up a yield stress, higher viscosity.
But there's an upper limit too. So here's a picture of if you
have too high a yield value then
back off. you That's not good for yourming
depositor either. So you can look at the Hershey's
Kiss, it's got a little bit of a
appeal to it, and I think they string, that's part of the
to even make it stronger. But you can imagine that if the
yield value is too high that's
space and cause problems if you want to put a wrapper on it.
So the yield value has to be
right shape, the right just right to get it in the
Hershey's Kiss. So that's one end of the
spectrum, something that gives
viscosity, and stands up when we us a high yield value, high
Candy bar? drop a dollop onto a conveyor.
there in your bag, right? That's like asking a give-away
question on an exam.
this kind of stuff, there's a But awhole bunch of theseikes
cross-sections on the Minnesota Science Museum.
They have some really cool quiz games, I could give you some
that you wouldn't get that are
So I want you to go ahead and ctake a cross-section of that
candy bar, preferably by biting it in half with your mouth, and
try not to smear it though, that's bad.
And then look at that cross-section, and you should
see something like that, right? And so what you see is a nougat
layer on the bottom.
top with a whole bunch of There'peanuts in there. on the
I guess that's what gives us the
It used to be a health bar. And then it's coated in
chocolate.
bar like this get coated in So how doechocolate?ate candy
It goes through an enrober, and this is a really cool piece of
thing.
We're doing a chocolate social We have one in our lab.
we'll crank up this enrober. with the Food Science Club, and
hopper that brings melted Achocolate up to the top.
And then there's a louver, this one has just holes in it to
allow the liquid chocolate to flow, and it forms a curtain of
liquid chocolate through which
So on the far right there, these pieces are conveyed.
on the far right there there's sorry, on the left-hand picture,
These look more like cookies uncoated bars.
principle is the same. than Snickers bars but the
uncoated Snickers bars packed Yotogether on a conveyor.se
They go through this curtain of chocolate, and the curtain of
chocolate covers those pieces so
side they're completely coated. Usually before they go through
this curtain they've
It's a little puddle it goes gone through a bottomer.
as well. through to get the bottom done
curtain and it's all coated Andaround with chocolate.the
Well suppose you had a really,
chocolate, what would happen to reallthat chocolate?cosity
Just flow right off around
bar with a really, really thin there, and you'd have a Snickers
None of us would be happy about that, much less M&M Mars.
So we've got to get the rheological properties just
right to give us the right
Also, if we want to put decorations on the side, on the
top, I don't if you spent some
you wolfed it down, but there's ta little swirl on there, ande
that swirl is, the property of
to the rheology again. giving that swirl relates back
rheological properties to make So you have to have the right
You could put a swirl there but if it's a thin, low viscosity,
it just flows right back in.
its levels. So it has to be thick enough and
high enough yield stress so that
it doesn't flow back down. you form a shape like that and
interest is. So that's exactly what our
So enrobing leads to coverage, And my tabs got screwed up here.
uniformity, leads to side coating, and if you don't do it
right you get feet and tails. So this thing here, I don't know
if you still have any of that Snickers bar left, whether
there's a tail down here at the bottom.
So it's sitting on a conveyor,
still flowing after it gets on, cso it goes through a conveyor's
with holes in it, a screen type conveyor and the chocolate flows
through the stuff that doesn't
But then it eventually goes on stay on there.
chocolate is still flowing to a solid conveyor and if the
So finding the right viscosity you're going to get these feet.
feet as well as giving the is important to eliminating that
it, as well as giving thickness of the candy bar, the thickness
of the chocolate on that candy
So what do we want in terms of bar.
yield stress versus plastic its rheolviscosity?perties,
We want something in the middle.
But basically we want something Itthat has enough stand upe.
properties to give us the thickness that we want on the
side without giving us the feet problem.
So sort of in the middle of the yield stress plastic viscosity
range.
Add more fat. Usually that's the way we do it
to get a thinner viscosity, lower yield value, to give us
the right rheological properties.
Okay? We got one more.
Well, there's one more and then a test.
And that's the Dove.
which means it's deposited into So this is a mold.ited piece,
And so if you can imagine a depression in a shape, and
inside that depression it has this shape.
The flat part is the top. So we're going to pour chocolate
into that shape.
find its level. ThOften we have to shake it toto
make it do that, but it's going to find its level and then form
that flat surface.
says Dove on it, Dove, is in the And so this part, the part that
that inverse Dove printed inside mold and the mold actually has
And so when we pour the chocolate in it has to be thin
enough to be able to flow into
You want to see something that's those fine cracks and crevices.
Go buy a Ghirardelli square. really, really fine?
really intricate pattern and So Ghirardelli square has this
it. And inside that ribbon it says
made in San Francisco.
Yes. >> Really?
[PHONE RINGING] It's inIt can't be mine. detail.
[LAUGHTER]
you can get out of a low It's incredible how much detail
something that will flow into any crack and crevice anywhere.
But seriously, go buy a Ghirardelli bar.
They're a little too expensive
so I bought these Dove pieces. for me to buy for you guys
too. They're pretty good chocolate
plant, the Ghirardelli plant, in And actually I was just at their
how they make those filled December, and it's interesting
So I wish I could demonstrate this in some way, but they pour
the chocolate into the mold, and
thickness that you would expect from the shape of the thickness
of that square. So they pour the chocolate into
the mold, and then they immediately turn it up side down
and shake it. And so all the remaining liquid
chocolate drips out leaving a shell of chocolate that's filled
up that mold with the fancy incredible printing that's on
the inside of that mold.
side up and then they deposit Awhatever filling they want inht
there and then they shake that
and then they put a dollop of chocolate on the top of each of
those and scrape them off into
how they make those squares of the cooling tunnel and that's
But again the shape, the filled chocolate.
that puts this to shame. intricacy of the printing on
making the Dove with the little flourishes, but the Ghirardellin
squares are pretty cool.
So what rheological properties So go look at that.
Well I've basically given it do we need here?
We've moved to the other end of the spectrum.
We want something that's really low viscosity, low yield stress
so we pour that dollop into the mold and it just flows into
every little crack and crevice
And so we want it to be down that we have in there.
type of chocolate. here in the thinner than thin
there? What do we have to do to get
More fat. Basically that's right.
So those Ghirardelli bars,
chocolate so thin that it fills them, is increase the fat level.
They wouldn't tell me what it was and probably if they did
I couldn't tell you anyway. But that's where we're going.
So very simple rheology.
but it determines what type of It's thickness and yield value
If we wanted to make a Hershey's chocolate we would use.
go that puddle. And if we wanted to make a fine
Ghirardelli chocolate mold
chocolate, we wouldn't see any square with a Hershey's Kiss
It would just flow, stop flowing shapes.
cracks and crevices. and it would never flow into the
really critical to the So getting the rheology is
that we're after. applAnd now for the test.late
We've all seen chocolate
What do you think they do to fountains, right?
fluid? make a chocolate that's that
Raise the cocoa butter. Yep, that's exactly what they
do. Interesting.
And that's warm enough that it's
It's probably 35 to 40, so it's always liquid, never going to
set up. [INAUDIBLE]
Actually, often when you
it's not real chocolate, see a fountain like that,
And so then it's made with some other fat that might have a
better rheological parameter. So you're right, it might not
be. [INAUDIBLE]
We call it compound coating.
tastes like chocolate, smells like chocolate, but it's not
made with cocoa butter. >> Man made?
Well, chocolate's man made. Well, machine made.
Okay. So again we have these as our
influences, but it's primarily
So everybody good with the fat content that we deal with.
So I have a few more minutes, I'm going to talk about
tempering and show some pretty
And all I have left for you is interesting videos.
[LAUGHTER] some lousy chocolate.
which is we've got that liquid So here we are in this process
In order to get it into a molded chocolate.
to crystallize the cocoa butter bar in just the right form,e got
otherwise we're not going to get
So we need to learn a little bit something that we like.
cocoa butter, its abcrystallization process.f
So we have to get the cocoa butter below its melting point.
So that's a cooling process.
degrees. Its melting point is about 34
So we have to bring it down It dbelow that temperature.ter.
It nucleates and forms a
liquid material. crystalline phase from the
triglyceride molecules, which look sort of like that, have to
come together to form a crystal lattice.
And then they grow out until we relieve the supersaturation
driving force and everything is at equilibrium, phase
equilibrium.
But of course life's not that Ssimple because the way these
molecules can come together is
So let me show you. So this is the melting process,
lower temperature you form a
But let me show it to you in crystal lattice.
So here's a video of, I've got pictures.
I think we're about 40 degrees cocoa butter on my microscope at
So it's melted, it looks black. This is cross-polarized
microscopy. So we've set the polarizers
crossed.
like if you take two Polaroid Soglasses and turn them 90ed
degrees.
No light gets through. Nothing gets through.
a little bit. WSo as the light passes through
the crystals, we can actually see the crystalline light come
through on our microscope.
So I'm going to cool this now at So that's cross polarizers.
the crystallization happen. a cerSo the stars come out.atch
So that's cocoa butter crystal
itself. I couldn't do it in chocolate,
couldn't show it to you in
many particles. chocSo they're in the way.too
I've got to show it just on cocoa butter.
So we cooled it down. It turns out that it solidified
at about 21 degrees.
and cooled it down, cooled it So we were adown.40, maybe 35,
It wasn't until 21 that the lights came on and the stars
came out. Now, I'm going to heat that back
up again, and watch what happens
So I'm heating it, I'm heating to the stars.
out. it, and eventually the stars go
And it melted at 27 to 28 So I medegrees.t fat.
So it's supercooling a little bit, and that's typical of
crystallization processes.
polymorph that I don't want. But what I got here is a
making chocolate without So then that's the problem with
wrong crystal structure. tempering it is it forms the
crystal structure based on its And I know it's the wrong
I could use fancy x-ray equipment to do the same thing,
but we know enough about cocoa
So what I mean by polymorphism butter so say that.
form different crystal is those same molecules can
together and organize. structures just by how they pack
of molecules. So a Fats happen to do it. types
A lot of drugs are polymorphic
pharmacists over there making sure that the drug we take,
drugs we take, are all in the right polymorph because the
right polymorph cures us, the wrong polymorph can kill us
because of the way it's bio-available.
So it's really important in the pharmaceutical world.
They live by polymorphs.
difference between a nice Ilooking piece and a crappy
looking piece.
to make sure that we've Bucontrolled that polymorphicus
structure.
say that these triglycerides So for us it's just enough to
that form the crystals can be packed in different ways to give
us different crystal structures of different equilibrium that
can stay and remain intact for a
So we think of cocoa butter as a long enough time.
That means when we cool it, it monotropic polymorph.
And gradually over time it forms forms a less stable polymorph.
So like most things it's trying to reach an equilibrium.
That equilibrium in this case is
butter triglycerides to pack the ability of those cocoa
lattice. into the tightest crystal
the equilibrium state. That's the lowest energy state,
What I crystallized in that previous video was a beta prime.
And I know it because I know
beta prime is. what the melting point of the
And that's been known, so this It's about 28 degrees.
So that's been known for many is that sayears.eo again.
If we don't do it right, we get this.
This is ugly bloomed chocolate
the cocoa butter in the right because we havway. crystallized
But we've known for many years
different polymorphic forms. that cocoa butter has six
of them. We're only concerned with three
down like I did, or cocoa butter Because when we cool chocolate
beta prime, this beta 1-2 formed down like I did, it forms the
temperature of 27.5. four which has a melting
in 1966, so we've known this This is some work that was done
And that's why I can say from where it melted, what polymorph
it was. But that's what happens when we
don't temper the chocolate. It just nucleates by itself into
what's an unstable form.
will show that video again, that And that unstable form, now I
the beta prime form. unstable form when this melts is
bloomed chocolate piece. And that's what gives us this
anybody has tried to make chocolates at home and didn't
understand the principle of tempering, this is what you got
the next day or that night. And that's not a pleasant sight.
It's got this whitish hazy stuff
good at all. on there that doesn't look very
just a second. And I'll show you a piece in
So what we're trying to do in chocolate is create this formed
five, a beta formed five
and it's got a melting point of ac34 which is perfect for ourl,
mouth temperature because then
Our body temperature is 37.8, but our mouth is a little bit
colder because it's open. Some more than others.
[LAUGHTER]
at or around 34 to give us a melted chocolate.
And it turns out that there's another more stable polymorph,
the form six, that's associated with bloom.
So this structure here is actually related to forming the
beta prime, and it quickly
gives us this ugly stuff here on transforms to the beta six which
[INAUDIBLE] >> Chocolate sauce and syrup
depends on how much cocoa butter
that same problem. is in there, but you can have
though. It could a[LAUGHTER]d growing,
This looks like mold, but it's not.
It's actually, we scrape this stuff off and the white stuff is
really just sugar and cocoa solids.
The fat actually contracts and
The brown part is where the mococoa butter is..
So in this particular type of bloom, those brown spots there
are cocoa solids and sugar
That's not going to hurt you. So what we have to do is control
how that cocoa butter crystallizes.
We can't just let it crystallize
It's going to go into an by itself.
We've got to turn it into something that is the right,
more stable form, that gives us all the right properties.
And that's called tempering.
the left here is taking a fully liquid chocolate, treating that
liquid chocolate in such a way
the right polymorph, and then thwhen this seeded or temperedf
chocolate solidifies, it turns
has all the right properties into a good solid chocolate that
So tempering typically involves heating to melt the chocolate.
So remember if we get a tanker
don't have to do that part. truWe just pump the melted we
chocolate into our tempering
But if we get bars or wafers chamber.
and then cool it down to a then we've got to first melt it,
26-27C, which is below the reasonably low temperature,
beta prime polymorph. And so we get both stable and
unstable, mostly unstable,
And then we warm it back up above the melting point of the
beta prime leaving behind beta crystals.
And that's what we're looking for is 1% to 3% beta crystals in
our cocoa butter so that when that chocolate sets, those seed
crystals overwhelm the rest of
all into the right stable the cobeta five polymorph.ts up
So that's our aim.
appearance, good snap, good contraction from the mold, and
resistance to bloom.
we've got tempered chocolate. Seriously, how it snaps, did it
come out of the mold, and is it resistant to bloom.
If we didn't do it right, we're going to see bloom in a couple
of days.
So it's pretty important to get the cocoa butter to crystallize
right.
and it's slightly undertempered, If we don't get it quite right
crystals we wind up with then we've got too few of those
the surface. chocolate that's got specks on
disk that I showed you but still Not quite as bad as that first
good nicely shiny chocolate. not quite as acceptable as a
butter seeds? BActually had a fellow from
Morinaga Chocolate in my lab
with this. last year and we were playing
We can also temper chocolate So these are his videos.
So these are little spheres, with seeds.
cocoa butter seeds that are used like a millimeter size sphere of
And you can see this little halo to temper chocolate.
Can you see it in the back? So it's a little halo in there.
It's going to appear really cool
I'm going to do the same thing. I'm going to cool that cocoa
butter, melted cocoa butter down
crystallizes. And so nominally, if I have a
seed crystal in there, it's going to take over and
crystallize the rest of the cocoa butter in the right
polymorph.
That seed is in the right
rest of this cocoa butter. So I want to be able to seed the
this and see what happens. So we thought, well, let's try
That seed crystal grows as we So here'scool. happens.
But the lights come on again. So that seed, the beta seed
crystal grew but then all around
unstable crystal polymorphs. it created these beta prime,
not enough to give us tempered So one single seed like that,
crystallization of the cocoa chocolate to overwhelm the
Now I'm going to show you something really cool.
I call this my supernova video. So I'm going to show you melted,
and then I'm going to explain what you see.
But watch it carefully. So I'm going to raise the
temperature.
go out, but there's a period of Ytime when we're between thets
melting points of the two polymorphs.
That means the more stable
But then I'm going to continue polymorph is going to grow.
melt. toSo you're going to see ato
supernova.
That's just cocoa butter. Isn't t[LAUGHTER] cool?
I'll play it again. It's really cool.
[LAUGHTER]
is that first we cooled and so we had a stable beta
polymorph at 34 centigrade. We cooled it at 21 or so that's
when the background stuff crystallized out.
But when they heated it back up again, so the beta prime
crystallized on there, when we
prime melted at about 27 just healike in the previous one.beta
But remember that beta crystal
So all in that time period has a melting point of 34.
and 34, that beta was growing. between when it was between 27
temperature where now the beta But then I reached the
collapsed back in. was going to melt and it
supernova. It looks kind of like a
So once we exceeded the melting point of the beta,
it's gone.
down we just see all the lights And so wcome back on. it back
Good question.
many seeds do we really need to Anget a nice shiny surface.ow
So he's good at marble tempering
that nice shiny brown surface. chocolate, and that gives you
we added determined whether we And depending on how many seeds
Whether we were back over here got close to that or not.
So I'm going to show a couple where tmore videos.k was.
This is .00055% seeds.
see them in here. But now you can kind of see that
there are some bigger blobs there surrounded by the smaller
ones. So again it's not enough for the
stable seeds to take over and dominate the cocoa butter
crystallization.
seeds there that we wind up with There's still enough of those
So it's a bloomed surface. a surface that looks like this.
fully bloomed. Not as bad as the first disk but
it. HerAgain you can see the betalt
primes are going to disappear first.
Beta grows and then it melts
So same principle. too.
with .137. Now let's do it again
where we have enough seeds that So tyou don't see much. now
Those seeds dominate and they take over the whole entire cocoa
butter crystallization. And then when you melt it,
it shows the same thing.
condition. They all melt at about the same
were a few beta prime crystals If you looked carefully there
but they were just overwhelmed nucleating in the background,
that's what gives you the nice by the stable polymorph and
So if you look at this last set of disks that I have in the bag
there, and you're welcome to
I did this talk once and some guy had put this in his pocket.
So how can you tell this is fat on the surface of the chocolate?
So this particular one is fat on
You can tell it by putting your finger on it, and hopefully your
finger is warm enough to
So this guy had put it in his pocket, and it was enough to
melt the chocolate. So you're welcome to taste this.
This is from 2001.
things in my storage room and then feeding it to my students.
[LAUGHTER]
is really cool. So we talked about improper
tempering caused by melting and then re-cooling.
So if you've had a chocolate bar
the day and it solidifies again at night during the summertime,
you open it up and chances are
really, really bloomed disk that it's going to look like that one
And that's because you've melted, you've broke temper, and
then you cooled it back down and
and you've got really ugly unstable polymorphs crystallized
We have this gradual bloom stuff.
happened with this. So this has been sitting in my
office or my lab now for years, and over time it's gradually
grown these cocoa butter
of the surface of this. And then in another version of
this talk, maybe chocolate 303, we'll explore Reese's Peanut
Butter Cups and how come they bloom faster than other
chocolates. So with that, just to summarize
there, so the surface discoloration on chocolate is
either these mounds of sugar in cocoa solids like we do in
untempered bloom or these crystals which are cocoa butter
crystals that grow out of the surface over time.
But again that's something for
So what I tried to do, I've run a little bit over here, no, it
was Tom that ran over...
Was, again, go back and talk [LAUGHTER]
chocolate came from. a little bit about where
spent a little bit of time going We talked about how it's made,
and different candy bars, chocolate bars, but then spent
some time on rheology of melted chocolate and tempering.
So I hope you understand
viscosity is important. It just looks like chocolate but
really there's a lot of science that goes into making this
chocolate the way it is, and
properties, the rheology and the these are just two of the
And then I'll leave bloom as a tempering.
the road. chWe've done some interestingown
work. Actually, let me leave you with
a question. So Reese's Peanut Butter Cups
has peanut butter center and
The peanut oil migrates into the chocolate outside.
So if you look at a Reese's Peanut Butter Cup that's old,
and I have some from 2008 in my lab.
[LAUGHTER]
next week, so I use them. Actually I have an agreement
with Hershey, and they send me a
I put half aside for next and use half this year with the half
from last, and we compare side by side the shelf life of
Reese's Peanut Butter Cups. So they can see the bloom, but
it's fat migration that causes
But here's a question: if you bake chocolate chip cookies--
You know where I'm going with this, if you bake chocolate chip
cookies, you have chocolate chips and a cookie dough, cookie
dough contains shortening, some fat migrates from the shortening
into the chocolate chip, have you ever seen a chocolate chip
bloom?
You have, Tom? In a chocolate chip cookie?
while. >> If it's been around for a
Maybe. >> Maybe a long time.
long. >> That's the standard answer is
they usually don't last that
I challenge you to find a chocolate chip on a cookie
that's bloomed, because it's rare.
But that's fat migration. In that case the fat migration
stops bloom, and that's chocolate 303.
So that's all I've got. No, wait a minute.
One more quiz.
What rheology is needed to make my Bucky chocolates?
Right, that's it. Thanks.
[APPLAUSE]