Thursday, 7 March 2013

The Science of Chocolate: Tempering

Chocolate contains two distinct types of fat, which melt at different temperatures.  Tempering is necessary to bring chocolate back to the correct crystalline form once it has been melted.  It is essential whenever you are using chocolate to make decorations or for finishing purposes, such as coating cookies and petits fours, or dipping chocolate truffles.

When the crystals in the chocolate are stable, it will be firm and easy to work with, whereas if it contains too many unstable crystals it will be uneven and streaky.  Tempering chocolate encourages the  formation of the right kind of crystals.  Successfully tempered chocolate has the following desirable characteristics:
  • high gloss
  • resistance to warmth
  • a pleasant aroma
  • a smooth mouth-feel
  • a longer shelf life
  • the chocolate will be crisp and snaps when broken
The undesirable characteristics of untempered chocolate are:
  • a white/grey colour or white streaks
  • vulnerability to warmth
  • dull appearance
  • a soft, flexibly consistency 
Before chocolate can be tempered, it needs to be melted.  Never let it come into direct contact with the heat source: it will burn.  The best way to melt it at home is with a bowl placed over a pan of gently simmering water, just make sure no moisture gets into the chocolate.  Here are the correct melting temperatures for chocolate:

Dark chocolate: Melt until it reaches 104-113 F/40-45 C.  Cool to 80-82 F/27-28 C.  Reheat to working temperature of 88-89 F/31-32 C.

Milk chocolate: Melt until it reaches 90 F/32.5 C.  Cool to 80-82 F/27-28 C.  Reheat to a working temperature of no more than 86 F/30 C.

White chocolate: Melt until it reaches 87 F/30.5 C.  Cool to 80 F/27 C.  Reheat to a working temperature of 82 F/28 C.

You will need a chocolate thermometer in order to get accurate readings of the temperatures.  Domestic chocolate tempering machines are available.  They are not cheap but they do work very well, and are worth considering if you plan to do large amounts of chocolate work regularly at home.

Although many recipes only need a little tempered chocolate for decoration, it is not practical to temper less than 300 grams at a time.  Decorations made from chocolate will keep for up to three months in a sealed container in the fridge.  Any leftover tempered chocolate can be poured on to a piece of baking parchment and then chopped up ready for cooking in recipes.

Here is a step-by-step guide to tempering chocolate at home:

1- Working in a cool, draught-free room, chop the chocolate as finely as you can with a large, sharp knife.  Place a little over two-thirds of the chocolate into a clean dry bowl (metal or glass).

2- Place the bowl over a pan of simmering water, making sure the water does not touch the base of the bowl.  there should be no water or steam coming up around the sides of the bowl (if any steam or drops of water came into contact with the chocolate, it would seize and be unworkable).  The water should be simmering gently, not boiling.

3- Melt the chocolate to the temperature specified about, using a chocolate thermometer to check it.  Stir very gentle with a spatula as it melts and do not leave it attended at any time.  When the chocolate is nearly two-thirds melted, remove the bowl from the pan of water and place it on a folded dish towel.  This prevents the bowl from sitting directly on the work surface, which would cool it too quickly and also keeps the bottom of the bowl dry.

4- Continue to stir gently; the heat of the chocolate and of the bowl will help to melt the remaining pieces of chocolate.  Add a tablespoon of the remaining pieces of chopped chocolate and stir until it has melted.  This process is called seeding.  Keep adding the chopped chocolate a tablespoon at a time and stirring gently.  The temperature of the chocolate will be reduced.  Be careful not to add so much chocolate that it no longer melts.  The aim is to reduce the temperature of the melted chocolate be adding small, room temperature, crystalline pieces of chocolate.

5- When the pieces of chocolate no longer melt, stop adding them.  The precrystallising state has now started.  The chocolate is beginning to come down in temperature and the crystals are starting to form a stable structure.  The chocolate now needs to cool to a temperature of 80-82 F/27-28 C.  If you leave the chocolate in a cool place and stir it from time to time, it will come down in temperature by itself.  The amount of time it will take to do this depends on the quantity of chocolate and the working environment. Use the chocolate thermometer to check on the temperature.

6- Once the chocolate has reached the correct temperature, it is at a stable level and fully tempered, but it is not at the best temperature to easily work with.  So place the bowl back on the pan of simmering water and bring it up to the working temperature given above.  As this is only a few degrees higher and you will be tempering a relatively small amount of chocolate, extreme caution should be taken to avoid bring the chocolate above the ideal temperature. (If this does happen, simply restart the cooling process.)  I suggest you place the bowl back on the simmering water only for a few seconds, as it will heat up very quickly and retain much of the heat. After five seconds, remove the bowl and stir gently, then check the temperature.  Repeat until the ideal temperature is reached.

7- You can test the chocolate to see if it has all the desirable qualities by dipping the tip of a knife into it and putting the knife in a cool place.  It should set in an even manner, be free of white streaks and have a high shine and gloss.  If it is not right, simply start the tempering process again

8- Keep the bowl of tempered chocolate resting on the folded kitchen towel while you work with it.  If it begins to cool down, you can warm it again so long as it does not go past the working temperature.

While this may some like a lot of work, let me assure you it completely worth it.  This process, though it may seem tedious will give you products a profession look, feel, and help give it a longer shelf life.

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