I am wondering what kind of glycerides of fatty acids affect crystallization, so I search more information, but I am not sure the answer. Some article point out palmitatic acid, stearatic acid, and oleatic acid many times. Are these three fatty acids the main matter of chocolate crystal?
If you notice the tag line for Chocolate Alchemy, it is about both the Art and Science of chocolate making. Today it is science. We are going to geek out on cocoa butter. Chemical structures, what that means, how to think about them….and why all that great information only takes you so far before you have to start bringing the Art into it.
Full disclosure. I am pulling a bit of my data from Wikipedia. But it is ALSO backed up by LOTS of cross referencing. https://en.wikipedia.org/wiki/Cocoa_butter.
And fair warning. Wall of text (and a couple pictures) ahead – plus SCIENCE!
Before we really get into it we rather need to talk the same language. In my previous life I was a chemist, so this stuff is as intuitive to me as the alphabet is to you. I also know that a large proportion of people go glassy-eyed at the thought of chemistry. But really, they are just words, and to my mind (yeah, I’m biased) pretty logical. So, some working definitions and explanations. Have a look at the following chemical structure.
The first thing is that this is called a triglyceride. Tri means 3. See the three sets of ‘lines’. That is why it’s ‘tri’. Those lines are called fatty acids. Look to the far left. Those three “O” attached by other lines? That is a glycerin structure. Also called the glycerin backbone. When things (those ‘lines’ or fatty acids) are attached to the backbone it’s simply called a glyceride. Just think of it as different tenses of a word. Stand vs stood. Glycerin vs glyceride. And since there are three fatty acids attached, it is a…..Tri-glyceride. The layman’s term for this is fat or butter (if it is solid at room temperature) or oil (if it is a liquid). It’s generally called a fat if it is derived from an animal and a butter if from a plant source. Hence cocoa butter. A room temperature ‘butter’ from the cocoa plant. Nice and simple.
Next, each of those fatty acids (the lines) have a different name depending on how long they are. Most of them have two names. I high and fancy standardized name, and their common name, often based on the source it was first discovered in.
From the picture above, the top fatty acid is hexadecanoic acid. It has 16 carbon atom in it (each of those jogs back and forth represent a carbon atom). Hexa means 6. Deca is 10. 10 + 6 = 16. Got it? Good. It’s also called Palmitic acid. Guess where they found it first? Yep, from the pressing of the palm kernel. Again, that simple. We are just going to use the common names.
Now, cocoa butter is not one fixed triglyceride. The picture above shows one possible triglyceride in cocoa butter. It is made up of Palmitic, Stearic and Oleic acid. One of each, in the order listed. But cocoa butter has other triglycerides (BTW, in the literature they are also called TriAcylGlycerides or TAG). To state it again, cocoa butter is a mixture of different TAGs. For ease of reference and reading, it is often referred (in context) as PSO. Just the first letter of each fatty acid. Have a look at this table.
There are 6 named “common” fatty acids plus the catch all ‘other’. Just from crunching some numbers (6 3 : 6 for the 6 fatty acids, 3 for the ‘tri’) there are 216 possible ‘common’ (meaning I excluded the ‘other’) TAGs in cocoa butter. In reality it is actually much less – thank goodness. Mostly there is POP, POS and SOS with smaller amounts of PLP, POO, PLS, and SOO. 216 down to 7. But from a chemistry standpoint, that is A LOT! Why do we care? Because each fatty acid has a different melting point and each combination (each TAG) has a different melting point and the proportion of those TAGs causes each cocoa butter to have a different melting point.
And THAT is why tempering is aggravating to so many people. Because each cocoa butter has the possibility to have a different TAG mix and therefore a different melting point. In point of fact, that we can temper cocoa butter at all is pretty damn amazing once you see just how many structures there are for us to work with. This is why tempering temperatures are given in ranges. Because cocoa butters come in different ranges.
Let’s look at a couple simple examples and delve into the chemistry a little so you hopefully can appreciate it, maybe understand it a little, and with a tiny bit of luck, see what you can do with that knowledge in a practical sense if you so desire.
Fact: the length of the carbon chain (C16 for Palmitic acid) is proportional to it’s melting point. C16 will melt at a lower temperature than C18 (Stearic Acid).
Why? Analogy time. You have three people holding hands and you have 10 people hold hands. Melting is getting everybody to let go. If you have to do it, which takes more energy (heat)? 10 people of course because there are more of them. It’s that simple.
But it isn’t THAT simple. That is true for straight chain fatty acids. But look at Oleic acid. See that extra line in there? It’s called a double bond ? Don’t freak out. It’s just a word. It means one of the people is holding onto something (a chocolate bar?) and can’t use both hands to hold together. The result is it takes you less energy to get them to let go (or melt).
That means that Palmitic acid (C16) melts before Stearic acid (C18).
Both Stearic and Oleic acid are C18. But Oleic has a double bond so it will melt sooner. If we look at the data of melting points, that is exactly what we see.
Palmitic 62.9 °C /145.2 °F
Stearic 69.3 °C /159.7 °F
Oleic 13.5 °C /56.0 °F
And how about if we look at Linoleic acid. It has 18 carbons but TWO double bonds. Both hands are full of chocolate! That is going to melt really easy. And indeed it does.
−5 °C /23 °F) to −12 °C /10 °F. (it’s a range depending on how it crystallizes (sound familiar?)
Bringing this all together, this means if your cocoa butter has a lot of TAGs with Oleic acid in it then it will melt at a lower temperature and you will have to temper it cooler than ‘normal’. And if it has a larger than normal proportion of Linoleic acid it’s going to really melt at a lower temperature. And if those percentages are higher, than your chocolate will tend to melt at a higher melting point.
So what does it all mean? Does it help you temper your chocolate? No, not really. It just helps you have some understanding as to some of the reasons that the chocolate you made from this year’s cocoa beans from Peru are not acting like last year’s. In point of fact, that quite often it DOES temper the same is somewhat amazing and miraculous given how small changes in TAG composition can affect just the basic melting point.
And we have not (nor are we really) even talked about how different TAG compositions crystallize together. Each different TAG will pack differently depending what other TAG is near it. And different packings mean different final structures, and those final structures are what we term the different polymorphic structures of cocoa butter. Our goal being Type V. But as you can start to appreciate now, just by the reality of different TAG being made up by different fatty acids in different proportions, they are a near infinite versions of Type V crystals. It is a whole RANGE of structures that are similar but not exactly the same. I mean how can they be the same when you can have cocoa butter with POP, POS, and SOO, TAG’s of all different lengths. I can’t be the same, therefore it has to be different or a RANGE of structures that behave and look similar!!
Confused? Yeah, that was a lot. What can you do with it? Well, If you are not adverse to it, you now have the tools to change something things systematically.
You may have heard about other oils and fats being added to chocolate. Yes, sometimes it is for financial reasons. Cocoa butter is expensive. But sometimes it is being done to change the melting point and therefore the tempering properties of the chocolate.
You have a chocolate that is just not holding temper? It melts too low? Well, have a look above. What melts higher? Palmitic acid does. And recall, it was named for being from palm oil. How about adding some palm oil? Sure, let’s look it up.
The palm oil TAG is still a mixture, but a lot of it is PPO and that will raise the melting point a bit.
How about palm kernel oil? Well, it has a bunch of Lauric acid that is C12 so that is going to make your chocolate melt at even a lower temperature.
Coconut oil I hear someone asking about. Well that is a funny one. Again, lots of Lauric acid (c12) but there are also C10 and C8 in there and when coconut oil is added to chocolate what you end up getting is a chocolate that does not bloom. Great you say? Well, no. It is also very soft (lower melting point) and does not temper either. Just because something does not bloom does not mean it tempers. It can do nothing. Sort of like a number line. To the right of zero is positive and that is tempered, left of zero is negative and is bloom…but there is still zero. Untempered. Coconut oil (in sufficient amounts) inhibits the polymorphic crystallization of cocoa butter.
At some point I want to experiment with small amounts of shea butter. It’s primary TAG is SOO. From all of our discussions here you would expect it to melt very low, but it doesn’t. Now, it’s not breaking any rules. Shea butter extract is a complex butter that in has many non-TAG (they are called nonsaponifiable) components that raise the melting point. To a surprising degree too. 89-100 F for regular shea butter and a special high melting point one that melts at 104 to 113°F.
I’ve found references it is tempering compatible (unlike coconut oil). There was a PhD research position I heard about a couple years ago where the goal was to come up with a ‘new’ form of tempered chocolate that would be more resistant to melting but still retain it’s nice mouth feel. I can see this is the direction the research would have to take. Very minor additions of select TAGs that give a shove the range of Type V crystal to the upper end.
Finally, I want to put the disclaimer in that I’m not advocating or against additions to chocolate. I’m neutral. The whole point of this conversation was to open your mind to possibilities and give a peek inside of some of the chemistry. I find understanding things terribly exciting.
Send in your Ask the Alchemist questions to firstname.lastname@example.org