Wednesday, 18 March 2009

Control your temper - long, complexe post

Many things in patisserie are simple in theory but tricky in practice; take rolling out a perfectly flat piece of pastry or dressing a row of eclairs of exactly the same size. Other things are easily done while relatively complicated science makes them work; like adding lemon juice to royal icing to make it whiter or whipping cream. One thing which is very hard to do and also really tricky to understand is working with chocolate.

As soon as you scratch the surface of working with chocolate you encounter tempering. You need to use properly tempered chocolate for molding and dipping. Properly tempered chocolate is shiny and has a good crack when you break it. It is also contracts on cooling so it is easy to demould. Chocolate which has not been properly tempered will remain soft at room temperature, be dull and liable to form a bloom.

I've read many different accounts of tempering and even heard first hand the explanations of three different chefs. While they've all explained the theory to differing degrees, none was actually able to make me understand why the tempering processes work. This has bugged me for an awfully long time. I knew all the theory, could even do the tempering, but did not quite understand how it happened.

Today, in the library at lunch time, I had an epiphany and suddenly the whole lot became crystal clear. I thought I would try and offer a really complete explanation for those who have been similarly plagued by chocolate doubt. It's not going to be quick... my prof always tries to make out that everything is easy but I cannot count how many times he has rolled his eyes, sighed and said, "C'est complexe, le chocolat."

What is the thing being tempered?

Cocoa butter is a rare polymorphic fat: it can crystallize in several different forms. (Think carbon forming coal, graphite and diamond.) Most sources seem to agree there are 6 possible cocoa butter crystals. Each has a different melting temperature and different properties. 

gamma16-18°CUnstable, soft, melts easily, dull
alpha21-24°C Unstable, soft, melts easily, dull
beta II26Unstable, no crack, melts easily, dull,
beta I27-29°CUnstable, melts easily, dull
super beta36°CStable but takes a long time to form (weeks)

The tempering processes ensure there are only beta crystals in the cocoa butter so the chocolate is stable, firm, cracks when you break it, shiny and melts around body temperature (in ya bouche).

More on crystals

One crucial fact that I was missing in my comprehension of tempering is that one crystal provokes the formation of other crystals of the same type around it. It's a kind of chain reaction.

Here is a clip of a different crystallization (the kind you get in gel hand warmers), showing how crystallization can flow outwards from a single trigger point (and, here, very quickly).

Beta crystals stack very nicely which is why they are stable, the chocolate is firm and it snaps nicely. Here is another way to help visualize those crystals and the chain reaction (and why tempered chocolate contracts!):

With that key thought in mind, it is clear that to temper chocolate you need to form some beta crystals which will trigger the whole chocolate mass to form in the same way.

How does that help?

Hopefully the above leads one to see that if you have some beta crystals pre-formed in your molten chocolate (and only beta crystals) then, as the chocolate cools, these 'seed' crystals will trigger the formation of other beta crystals. Thus the solid chocolate will consist only of beta crystals. Whoop.


Thus we can say that the aim of tempering is to bring the chocolate to a state where the only crystals present in the molten mass are beta ones. This is why some people prefer to call tempering 'pre-crystallization'; you're setting up some seed crystals so when the whole mass of chocolate crystallizes, the right sort form.


There are many different ways to do this. Today I am going to take on the classic method of 'tabling' chocolate.


What is tabling?

I first saw someone tabling chocolate at a younge age on that Lindt advert from the mid-90s. Tabling is when you pour a load of molten chocolate onto a granite/marble/stainless steel surface and work it with a palette knife or two. If you didn't grow up liking chocolate in the 90s, here's a clip of someone doing it on YouTube for an awfully long time with a great soundtrack. Unfortunately the chap's disabled embedding so you'll have to click away to see it. 

Watch clip here.

What's actually going on here?

Very simple: the chocolate is cooling down. Apart from the intense satisfaction, there are good reasons to do it this way rather than just leave it in a bowl. By spreading the chocolate out it cools quicker. By keeping it moving, it ensures the chocolate cools uniformly and no lumps are formed.

How this tempers the chocolate

The tabling action itself is only a part of this method of tempering. Here's what's going on:

1. The chocolate is heated to c.45°C. At this temperature (see table above) all the crystals have melted so we have a tabula rasa.

2. About 2/3 of the chocolate are tabled. As the chocolate cools quickly, it thickens and a variety of all the different crystals form, including our wanted betas.

Now the aim is to get rid of the other crystals and leave just the betas. This is easy since our betas have the highest melting point. All we need to do is gently re-heat the choc. So...

3. The chocolate is scraped off the table and back into the bowl where the remaining chocolate gently raises its temperature. Once the chocolate heats back up to c.30°C all crystals will have melted except our betas. If the remaining chocolate is not sufficient to raise the temperature all the way, the whole lot should be heated very gently. (Since clearly, if heated above 35°C, the whole process has been wasted since the betas will melt, too.)

Thus we have a bowl of chocolate containing only beta crystals. Ready to use. As the chocolate cools, further beta crystals will form around the beta seeds meaning our chocolate will be just as desired.

While you can feel your way through this process with a thermometer, it's not the temperatures that are crucial but, rather, the texture of the chocolate which reveals the state of crystallization. You can actually follow a tempering curve perfectly (45-27-31°C) and end up with badly tempered chocolate. We are learning to do the whole process by touch (which does take time).

In essence, you know you've reached step 1 when the chocolate is perfectly runny and rather warm to the touch. You know the chocolate is sufficiently cold during step 2 when it has got much thicker (but still just flows). You know you're hot enough during step 3 when the chocolate is just below body temp. We always do a little test by dipping some greaseproof paper or a knife tip into the chocolate and seeing that it sets quite quickly, without marbling or going dull.


This method begs a lot of questions like, (a) Why not just gently melt the chocolate until it hits 30°C? or, (b) Having heated to 45°C why not just cool it 30°C? At least, these are the thoughts that crossed my mind. I'll take the questions on in another installment but as a brief, brief answer, these methods ARE possible but to do (a) you have to melt the chocolate very, very slowly to ensure the chocolate is nice and fluid to work with while to do (b) you need a clever piece of kit to balance the fine temperatures perfectly and prevent the wrong crystals forming.

There are also quite a few more details to fill in like the fact that dark, milk and white chocolate need to be tempered at slightly different heats and the fact that certain chocolate (i.e. couverture) is the kind you need for good tempering.

But it's getting late.

1 comment:

  1. It’s all crystal clear now! Perhaps you should become a science teacher; really enjoyed the first lesson.

    Thanks for taking the trouble.