Q:  In cooking, what does it mean to temper something?

-- Rochelle

Tempering refers to the blending of ingredients of different temperatures.  There are two common uses of the term, to temper eggs or to temper chocolate, although the way tempering works differs between the two.

In tempering eggs, you add a small amount of a hot liquid into relatively cooler eggs in order to warm them up without scrambling them.  This method is used in making custards, egg-based sauces, and other foods where eggs are used to thicken a hot liquid.  If you simply dumped the eggs into the hot liquid, the heat would transfer immediately to the eggs causing them to scramble.  To avoid this, the liquid is removed from the heat and a small amount is poured slowly into the beaten eggs while they are whisked.

This has three effects.  First, it warms the eggs up so that they are closer to the temperature of the liquid to which they are being added.  By doing so, you reduce the impact of the temperature shock between the hot and cold ingredients.

Second, the liquid added to the eggs distributes their protein molecules, and opens out the chemical bonds.  This has the effect of encouraging the formation of the protein web which causes sauces to thicken.  Other molecules in the hot liquid may also help to raise the temperature at which the eggs will curdle.  See the posting Custards and Sauces for more details

Finally, while you are tempering the eggs, the hot liquid, which has been sitting off heat, has had a chance to cool down.  In my own kitchen, two cups of water boiled in a medium saucepan took just under one minute off heat to cool below 180°F (82°C), the critical temperature in making egg-based sauces.  When you stir the tempered eggs back into the other liquid, the temperature drops a bit further so that it is now at an ideal point to reheat until it thickens.

In chocolate making, the goal is to produce a smooth, shiny chocolate which melts in your mouth.  It turns out that the fat in chocolate, cocoa butter, solidifies into six different forms, only one of which makes good chocolate.  To achieve this form, the chocolate has to be tempered using one of two techniques.

In the classic technique, the chocolate is melted and brought to a temperature of around 115°F (46°C).  Two thirds of the chocolate is then cooled by working it on a marble slab until it reaches 80°F (27°C), and then gently stirred back into the other portion, which has been kept at about 100°F (38°C), being careful not to incorporate air bubbles.  The mixture is then heated back to a temperature of between 85°F (29°C) for milk chocolate and 90°F (32°C) for dark chocolate.  If it is too warm, it is stirred until it cools down to the desired temperature.

In the second technique, called quick tempering, only two thirds of the chocolate is melted to 115°F (46°C), and then the other third, which has been chopped into small pieces is stirred into the melted portion until it has reached the desired temperature and is completely smooth.

In tempering both eggs and chocolate, ingredients of differing temperatures are combined to create the desired outcome.

[For information about how one of the most advanced scientific tools available, synchrotron radiation, was used to unlock the secret of making chocolate click this link.]