Chocolate and Tempering.
Melt a bar of good chocolate and let it set again: it comes out dull, soft and streaky grey. Same chocolate; different crystals.
Chocolate is cocoa solids and sugar suspended in cocoa butter, and its texture is the cocoa butter's. Cocoa butter is a fat of unusually uniform molecules (V.6) that can pack into six different crystal forms, numbered I to VI, each melting at a different temperature: about 17, 23, 25.5, 27.5, 33.8 and 36 °C. Only form V gives what we want: a glossy surface, a clean snap, a set that shrinks slightly so it releases from moulds, and a melt just below body temperature. Chocolate left to set on its own forms a mixture of the unstable forms, which slowly convert, pushing fat to the surface as a grey, streaky bloom.
Tempering steers the crystals. Melt the chocolate completely to about 45–50 °C, erasing all memory of crystals. Cool it, stirring, to about 27–28 °C, where forms IV and V begin to grow. Then warm it gently to the working temperature — about 31–32 °C for dark, 29–30 for milk, 28–29 for white — which melts the unstable forms and leaves only form V as seeds. Stirring spreads the seeds; as the chocolate sets it follows their lead. Seeding — stirring chopped tempered chocolate into melted chocolate at about 34 °C — does the same with less work. The workshop takes chocolate through the curve.
Below: the melting points of cocoa butter's six crystal forms against the chocolate temperature you choose: the forms that would be melted at that temperature and those that could survive, with the tempering steps for dark chocolate marked.
- Explain cocoa butter's crystal forms.
- Temper chocolate by the curve or by seeding.
- Recognise bloom.
- Store and melt chocolate.
Melt, cool, rewarm, stir
At 31.5 °C, forms I to IV are all molten and form V, melting at 33.8 °C, survives: the chocolate is tempered if form V crystals are present to seed it. At 35 °C even form V melts, so overheated chocolate loses its temper and must be taken through the curve again. Below about 27 °C the unstable forms set first, and the chocolate will be dull and soft and will bloom. Test before using: smear a little on foil or a knife; tempered chocolate sets in about five minutes at room temperature, glossy and snapping.
Practical tempering (dark): melt two-thirds of the chocolate over barely simmering water or in short microwave bursts to 45–50 °C; stir in the remaining third, chopped, to cool it to about 31–32 °C, stirring until the pieces melt (seeding); test; keep at 31–32 °C while working, rewarming briefly if it thickens. Keep water and steam out — a drop makes chocolate seize into a grainy paste (X.1). Store chocolate cool (15–18 °C), dry and away from strong smells; fat bloom from warmth and sugar bloom from damp both spoil its look but not its safety. For ganache (chocolate and cream, X.1), no tempering is needed.
Melt and reset a square of chocolate without tempering, and temper another by seeding. Compare gloss, snap and how they melt on the tongue.
Terms
- Tempering
- Setting chocolate so its cocoa butter crystallises in form V.
- Form V
- The crystal form that gives snap, gloss and a clean melt.
- Bloom
- Grey streaks of fat or sugar on badly set or badly stored chocolate.
- Seeding
- Adding tempered chocolate to melted chocolate to supply form V crystals.
Sources
- R. L. Wille and E. S. Lutton, "Polymorphism of cocoa butter", J. Am. Oil Chem. Soc. 43, 491–496 (1966): six crystal forms melting at about 17.3 (I), 23.3 (II), 25.5 (III), 27.5 (IV), 33.8 (V) and 36.3 °C (VI); form V gives tempered chocolate its snap and gloss.
- A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.
- H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.