Phase transformations: chocolate edition
Sunday, November 20, 2011

In our theory classes last week, we learned all about chocolate making in preparation for our chocolate egg sculptures and chocolate confections (next week). Chocolate comes from the seeds of cocoa pods which are the fruit of cocoa flowers. These flowers grow on the trunks of cocoa trees found in tropical rainforest climates.

The variety of cocoa trees, the terroir, and the conditions of fermentation and drying (of its seeds) all have an effect on the quality and flavour of the cocoa seeds. The fermentation and drying of cocoa seeds have to occur immediately after harvest and are done on-site. Then, the dried seeds are shipped off to chocolate manufacturers who clean and roast the seeds to develop their optimal flavour. Afterwards, the seeds undergo micronizing (break seeds into pieces) and winnowing (remove the shell from the cocoa nibs inside).

On the top is a dried cocoa pod. When the cocoa pod has just been harvested, it has a thick rind which surrounds a moist pulp of 30-50 cocoa seeds. The seeds in whole are in the picture on the right. On the left is a seed broken and shell separated from the nibs (darker brown).

The separated cocoa nibs (45% cocoa solids, 55% cocoa fat) are ground into chocolate liquor (unsweetened pure chocolate) which can either be used directly to make chocolate or separated into cocoa powder (from cocoa solids) and cocoa butter (from cocoa fat).

The cocoa pod (1) holds a handful of cocoa seeds (2) which are separated into cocoa nibs and shells (3). The shells are discarded so that you are left with just the crushed nibs (4). These nibs are processed into cocoa liquor (5) which is separated into cocoa powder (6) and cocoa butter (7, yellow chips).

For the chocolate liquor that will be turned into chocolate, the milk, sugar and lecithin (emulsifier to improve flow) are added at this stage. Then, the chocolate mixture is further refined to reduce the particle sizes so that it will melt more smoothly on the tongue. The final stage is conching where acids (from fermentation) and any moisture are removed, and the chocolate is heated and mixed to improve the flow and homogeneity.

To make chocolate, the cocoa powder (1) and cocoa butter (2) are combined with sugar (3) and milk solids (4) to get chocolate (5).

But we’re not done yet! We’ve only come as far as what the chocolate manufacturers are concerned with. Now the chocolate is shipped off to the artisanal chocolate maker who must temper the chocolate before molding. Chocolate has to be tempered properly to have a glossy surface, correct firmness, and nice snap when you break it. If not, you will have chocolate that will never set or have unattractive white deposits (called bloom) on the surface.

Tempering chocolate is the process of melting and cooling the chocolate in such a way that the cocoa butter crystallizes in the correct form (crystal structure). The cocoa butter can crystallize into 6 different forms (Form I – VI), each differentiated by a different melting temperature. Different crystal forms are created as a result of the cooling rate.

Melt chocolate to 50°C.

The first step in tempering chocolate is to melt it to 50°C to remove all existing crystal structures from the cocoa butter. This is now untempered chocolate.

Now, there are 2 ways to temper the untempered chocolate. Both methods involve cooling the chocolate down to 29°C at which crystallization of the cocoa butter begins. Then, we reheat the chocolate to 31-32°C and hold it indefinitely during use. We must reheat the chocolate so that the undesirable crystal forms are removed (melted) and the correct crystal form remains (called seeds). These crystal seeds promote correct crystallization of the remainder of cocoa butter when the chocolate is setting.

The first tempering method is called the tabling method. It involves spreading the chocolate on a marble surface to thicken it while cooling it to 29°C. This constant movement accelerates the crystallization process.

For the tabling method, we pour out half of the untempered chocolate onto a marble surface and work it with a triangular scrapper and spatula.

To work it, we scoop up some chocolate with the scrapper and scrap it off with the spatula and repeat so all the chocolate is evenly worked. We have to work fast to ensure none of the chocolate sets on the marble surface.

The second tempering method, seeding, is easier and cleaner. We cool the untempered chocolate by adding chopped pieces of tempered chocolate. These pieces already have the correct crystal structure and serve as the seeds for promoting correct crystallization of the remaining liquid cocoa butter in the chocolate.

Adding pieces of chocolate to seed the untempered chocolate as it cools.

After all that work, we spread a thin layer of our tempered (hopefully) chocolate on a spatula and let it sit for 5 minutes to set. If it sets, you’re good to go. If not, start again.

With our tempered chocolate, we practiced making chocolate eggs with molds. This is in preparation for our final chocolate egg sculptures to be made later. For our chocolate egg prototypes, we make 2 half shells and then attach together with melted (tempered) chocolate.  To make the half shells, we first paint a thin layer of chocolate on the mold, let it set, then fill the mold with chocolate and pour it out so a thin layer remains. If it’s properly tempered, the chocolate should set within 15 minutes and pop out of the shell easily.

Here's my first chocolate egg.

My second chocolate egg. I'm very proud of the shinyness of this one. That's what properly tempered chocolate will get you!

Then, we made some tacky-coloured marzipan flowers for the egg.

My third chocolate egg, made with piped tempered chocolate and modeling chocolate. The modeling chocolate is made from chocolate and glucose and tastes like a tootsie roll.

By the end of the week, I got tired and lazy and didn’t pay enough attention while tempering my chocolate. This resulted in re-tempering my chocolate 4 times. We also had free reign to make whatever we wanted on Friday. This turned into a lack of planning on my part, which then became a balancing act of whatever chocolate shapes I had formed.

The ‘bubbles’ in my chocolate egg were created by sticking gelatin shapes in my mold before pouring on the melted chocolate. After the chocolate sets, you just peel away the gelatin from the chocolate, leaving behind a shape.

My fourth chocolate egg. You can't tell too well from this picture, but my chocolate was the least well tempered compared to previous days. The surface of my egg and other parts were all a bit matte.

One Glorious Comment
  • David Iles
    November 23, 2011
    Well done, these look amazing!