How Chocolate Tempering Works

When you buy commercially available pure chocolate, it has already been tempered by the processor as the final step when transforming cocoa beans into high quality chocolate. You can tell it has been done by looking at and tapping your chocolate bar -- it should be shiny, sound hollow when tapped, does not break easily when you try and take a piece from it and has all of the attributes of well-tempered chocolate previously described above.

When you melt chocolate for your own use, you in effect break the temper from the processor and its crystals separate into four types: beta, gamma, alpha and beta prime. The beta or good crystals are lost somewhere in the molten chocolate and and when it cools, the last three crystals contribute to a chocolate that won't fully harden and will have a streaked and dull sheen, called a "bloom". However, the densest and most stable form hardened chocolate (cocoa butter) can take is called the beta form, achieved only through tempering.

SARAH SAYS: Tempering chocolate is analogous to melting a stick of butter. Butter, like chocolate, has been previously melted and tempered by the producer in order that it hardens to a proper consistency and looks presentable when we buy it.  At home, when we melt it again for our own use, the solids and fat separate - this can be seen clearly in the pan; the solids are the small clumps in the pan. If the separated butter is cooled as is, it won't harden properly. The solids and fats must be reheated again to re-combine them, so when they harden, they do so as a solid mass.

Tempering ensures that the beta crystals in the chocolate are not lost when melted and that it will harden back with its original crystalline pattern, all with a uniform size, resulting in all of the desirable traits of good chocolate confections and decorations can have. Beta crystals are composed of triglyceride molecules interlocked in a way that makes them most resistant to melting (they have a melting point of about 95 or 96 degrees F and most resistant to physical distortion (this is the reason the chocolate snaps rather than bends and doesn't set when cooled). The percentage of triglyceride molecules that are in the beta crystal form (seed crystals) determines how thick the chocolate is (and, hence, how it flows), how it cools, and how it will eventually appear. Too few crystals and the chocolate won’t harden or contract properly; this is called under-tempered chocolate. Too many crystals and it may be too thick for enrobing and dull in appearance; this is over-tempered chocolate.

When chocolate is tempered, you get these desirable attributes:
Appearance. Tempered chocolate releases easily from a mold and keeps at room temperature for months without discoloring or becoming streaky. Have you ever had the experience of opening a bar of chocolate found in a cabinet that was stored far too long, and finding a grayish, powdery surface on the chocolate? This is called "bloom". It doesn't actually affect the taste of the chocolate at all, but it doesn't look nice. Untempered chocolate used for confections and molding, develops serious bloom in 24 to 48 hours, and it never gets the beautiful shine of tempered chocolate.

Solidity. Well-tempered chocolate sets hard, snaps crisply when broken, gets a lustrous sheen, feels dry to the touch and smooth in the mouth. Untempered chocolate never develops the hardness or "snap" that one expects from a piece of chocolate. It can be very messy to serve in warm conditions.

Mouthfeel. Tempered chocolate melts at a specific temperature (1-2 degrees below normal body temperature) for a perfect mouthfeel. This is very important. The texture of bulk untempered chocolate is highly unpleasant and the flavor doesn't develop properly in your mouth. It's just not right.

HOW CHOCOLATE CRYSTALS WORK
Chocolate is made up from crystals. What are they?

Cocoa butter molecules link together in several different crystalline forms given the names of Greek letters—beta, gamma, alpha and beta prime. ( Beta and beta prime are both called beta crystals). The most basic differences among them are melting point, density, and stability. 

Crystals are molecules linked together in three dimensions. The temperature below which a liquid becomes solid through crystal formation is called its freezing point. For example, ice is the crystalline form that molecules of water take when they freeze or solidify. Even though the word "freezing" is normally associated with the idea of coldness, it is clear that there are many substances (like chocolate) that are solid (or "frozen") at room temperature and whose freezing point is actually fairly warm. Conversely, crystals dissolve (that is, they melt) when subjected to temperatures above this point. In the case of water, the freezing (or melting) point is a single temperature—32 degrees F (0 degrees C)—because water consists of a single type of molecule. Cocoa butter crystals, however, being made up of a variety of triglyceride molecules, freeze and melt over a range of temperatures determined by the individual melting and freezing points of the specific molecules present.

How does crystal formation transform a liquid into a solid?
As more and more crystals are packed into a limited space a liquid will gradually solidify. Crystal growth occurs either by an increase in the number of individual crystals or by an increase in the size of individual crystals. Small, evenly distributed crystals of similar size create a solid with uniform density, while a combination of large and small crystals creates a solid of variable density. The more tightly packed the crystals within a limited space become the denser or harder the solid becomes.

What does stability mean in the world of crystals?
In the simplest terms, stability means that a crystal (or a solid made from crystals) is unlikely to change once it takes a particular form or shape. Another way of thinking of stability is that more energy (e.g., heat or physical force) is required to disrupt the shape of more stable crystals. Imagine that triglyceride molecules—the building blocks of crystals—are chairs designed to stack. If the chairs are placed one on top of another, the space between the chairs is reduced to the minimum—a measure of density—and the stack itself is virtually impossible to disrupt by pushing and pulling—that is, they are stable. If, on the other hand, the chairs are randomly thrown together, there will be large spaces between the chairs and much less force will disrupt the pile. To complete the analogy, the most desirable cocoa butter crystals are dense and stable.

What are the basic principles of tempering?
There are two basic concepts that underlie successful tempering: formation or addition of the correct seed crystals and proper cooling and heating to make certain that these crystals are present in ideal numbers. Seed crystals are beta crystals, which, by growing larger, eventually cause the liquid chocolate to solidify. In chocolate that has been heated to the point that the cocoa butter has no crystals present, beta crystals can then be formed by lowering the temperature to no less than about 84 degrees F. It is important to remember that crystal growth requires time. (This step can be by-passed by using previously well-tempered chocolate to provide seed crystal.) Once seed is formed, it is stirred into melted chocolate. Stirring has two essential effects: the equal distribution of seed crystals and the equalization of temperature throughout the mass of chocolate. As stirring continues the chocolate will begin to thicken. It is at this point that small changes in temperature will control the amount of seed present. Slight cooling will cause growth of additional seed crystals. Slight heating will reduce the number of crystals.

Why is the number of seed crystals so important?
It is, of course, impossible to know how many seed crystals are present as you temper chocolate, but The ideal number of seed crystals is probably only about 1% at the time the cooling process begins. Judging when you have reached this point is a function of practice and experience.

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