Ask the Alchemist #77

Hi! so i understand that when working with dark chocolate you have to melt it to 45-49 C. and then cool it to 28C. Then reheat it to 32C, to melt out all of the unstable crystals. But is it possible to just skip the middle step of cooling to 28C? What if i just melt the chocolate and cool it down to the working temp of 32C and then pour it into my molds? This way won’t I be maintaining a temp high enough to melt the unstable crystals while keeping the stable form 5 crystals? What after all is the purpose of cooling to 28C then? At what temp do stable form 5 crystals start to form after melting?

This is a really good question and one I have received over the years quite a bit. And I have to say it stumped me for a while. Really, it makes perfect sense…in theory, but it fails in practice…or does it?

CAUTION: SCIENCE CONTENT AHEAD (but only a little)

So why does it not work? Let’s look at what you are trying to do, and what you are and are not doing if you don’t reduce the temperature to 28C/80F.

Solid chocolate is by definition 100% not liquid. I don’t say 100% crystallized because technically it can be amorphous or without crystal structure, or a mixture of amorphous and crystal structures. In totally untempered solid chocolate we can estimate that 20% is Type V and the rest are types I-IV (this probably actually isn’t true due a whole host of reasons (rates of crystallization in contaminated polymorphic system would sum it up) but close enough for the example). With that number in hand, we can see that we can have up to 20% Type V crystals when we bring the temperature down to ‘seed’ temperature, i.e. that point where the chocolate just starts to thicken a little. The cooling step of 28C/80F. In actuality, it is probably much less than 20%. Maybe 10-20% of that, the rest being Types III-IV (types I-II form much lower) and un-crystallized liquid chocolate. So, with a little rough math, that means there is probably 1-2% type V crystals.

Now, what I find terribly interesting about my ‘back of the envelope’ calculation is that that number is very close to the recommended amount of seed chocolate (i.e. 100% type V) you should add if you are tempering by seed. Why? I’m glad you asked. It comes down to a concept called nucleation. In layman’s terms you have to have a nucleus or SEED for the rest of the chocolate to form around and experience shows that for chocolate you need at least 1-2%. Below that and either the crystal formation is too slow, or there are too many places in the solidifying chocolate that are ‘un-seeded’ so other crystals start to form instead.

So, why does it not work to bring your chocolate to 32C/88F and then let it cool? Well, if you followed what I was saying above, it can only be because you don’t have enough Type V crystals. You are below the 1-2% threshold limit for proper Type V propagation. And that is because crystallization is heavily temperature and concentration dependent, and polymorphic crystallization is even MORE dependent on those two conditions. What that boils down to is that you are not giving it enough time at 32C/88F. (DISCLAIMER: I am totally making this next part up, but keep in mind I’ve many years as an organic chemist, so have a reasonably good gestalt feel for this kind of thing. And I am backing it up with the fact that we know that holding at 32C/88F doesn’t work.) In order to reach 1-2% type V at 32C/88F you may well have to keep it at that temperature for 24 hours. Or 48 hours. Or longer. Even if it was only 4 hours, that is quite a while if you want to temper NOW. And to make matters worse, generally speaking, crystallization is not a first order rate of reaction in regards to temperature. This means that if at one temperature (say 28C/80F) you are forming 0.1% Type V per minute, a couple of degrees warmer won’t reduce it just a little to 0.6% or 0.8% per minute, but will probably reduce 1-2 orders of magnitude, meaning just a couple degrees higher and you are down to 0.01 or 0.001% per minute…and you need to get to 1-2% and you want to raise it 5-10 degrees? You can see why it does not work.

Basically what you should get out of this is that the melting point of a crystal (94 F for Type V) is not really related to its formation speed at all, except the formation rate is zero at the melting point, i.e nothing can form if it is melting. All other bets are off.

To explicitly answer your question, the purpose of reducing your chocolate to 28C/80F is to create 1-2% Type V crystals ‘in a reasonable amount of time’.

One final science tidbit that I won’t (and can’t, I just don’t understand it well enough myself. Basically a variant of a variant of a Feynman quote “If you can’t explain it to a six year old, you don’t really understand it.”) explain. It is in regard to your comments about stable and unstable forms. There is a general truism of polymorphic systems (i.e. compounds that form multiple crystal structures). It is that the LEAST stable forms are the forms that form first. So, Type V is the least stable. And really, this makes sense. If it were the most stable, we would not have to work so hard to form it and keep it. It would just happen…but it doesn’t, does it?

Class adjourned.

Go rest your brain and have some chocolate.

And keep those questions coming.

—– Submit your Questions to the Alchemist: question(youknowtoremovethisright?)@chocolatealchemy.com —–

4 Responses to “Ask the Alchemist #77”

  1. I’m wondering–do you know what the minimum % of type V is needed in the end to have good temper, and what is the maximum to the point where it is over-tempered and not workable? I had always thought that tempered chocolate was mostly type V but it sounds like the % is a lot lower.

  2. Tom,

    Actually, it is probably very close to100%. You did not misunderstand that.

    To clarify, you only have a few percent or so as it is setting up and still liquid, but then the majority of it forms around those seeds crystals..

  3. So it’s 1% to 2% type V when you are done tempering, and I imagine smaller % of the other types when you pour into the mold, with the rest being liquid? And then the crystals form as the chocolate is cooling in the mold?

  4. […] Chocolate Alchemy: Is there a tempering shortcut? […]

Leave a Reply

Instagram

facebook.png



Articles and other Helpful pages

Alchemical Formulations
(Recipes)