Wacky weirdness while working with wchocolate

Chocolate is interesting stuff. When the Spaniards were first exposed to xocoatl by the conquered Aztecs, they treated it sort of like a dirty little secret -- massive amounts of it shipped back to Spain without explaining to anyone else what these weird, bitter tropical seeds really were. When it was truly figured out by the English and others in Europe, it became wildly popular, first as a beverage (from a bitter water-based beverage with chiles to the modern milk-based, sweetened hot chocolate we know now), and then as refining techniques improved in the 19th century as a candy. That's some fascinating history, but you wouldn't be reading this if it was a history post, right? So I'm going to have you make a cup of cocoa instead.

If you're used to getting a cup of cocoa out of a packet, the rigmarole you have to go through to make it from scratch might be startlingly complicated: get a microwave-safe mug, some cocoa powder, milk, sugar, and a pinch of salt, and bring a pot of water to a boil. Put 2 teaspoons of cocoa powder, a tablespoon of sugar, and the salt, and splash in a tablespoon or so of hot water. Stir it up until it makes a smooth mixture, then top up the mug with milk and stir furiously (the Mexicans even have a special whisk for this called a molinillo), then zap in the microwave for 90 seconds or so on high and stir again before drinking. That's... not a particularly simple process. It does make better cocoa than what comes out of the packet, but is it really necessary? Why can't we just slap all the ingredients we have in together and zap it? (Go ahead, try it. I'll wait.)

That scorched brown foam on the top of the second cup -- not that appetizing, is it? With some work, you can stir it in eventually and it might not taste too bad. But if you compare it with the first cup, it's a little rough around the edges and just generally more trouble than it's worth. It turns out that the powder they put in cocoa mix is more than just sugar and cocoa -- dried milk gives it body, and lecithin, a very common emulsifier often derived from egg yolks or soybeans, helps to eliminate the need for the stirring. Now wait a second... emulsifier? What if I just used skim milk? Heh. It's never that easy.

To understand what cocoa powder is, you have to know a little bit about the process. Cacao beans come off the tree not tasting much like what we know as chocolate. They have to be fermented and roasted to develop flavor (as well as the dark brown we associate with chocolate, coffee, and caramel); the roasted beans are then de-chaffed and the starchy cotyledon of the beans (known in the trade as nibs) are crushed. The end result is known as chocolate liquor, and it is a brown paste consisting of a suspension of cocoa particles (the starchy roasty bits that give it the flavor) in fat (cocoa butter). The difficulty working with chocolate comes from the fact that while the typical piece of chocolate seems homogenous on a macroscopic scale, in reality it's anything but; the result is that when cooking chocolate in almost any form, the processes you use have to reflect that. While the cocoa butter is usually drawn off and either added back in to make solid chocolate or sold for different purposes, the finished chocolate liquor retains a fair amount of it (sometimes up to 25%, depending on the brand), which in turn goes to provide mouthfeel in the finished cocoa powder. Even if you have skim milk, then, there will still be fat in the cocoa powder to complicate the mixing process. That's why large scale makers of cocoa mix add emulsifiers like lecithin to the mix, and in fact you'll even find it in many forms of solid chocolate (particularly milk chocolate).

There's a bit more to it though, much of which has to do with the curious physics of cocoa butter. Unlike many fats, cocoa butter has a fairly sharp melting point (around 32C), as well as a tendency to form several different kinds of crystal lattices under various temperature conditions. The most stable form, the beta crystal, is the ideal, melting at around 34C, but without proper care, the cocoa butter will often congeal in less stable forms. Ideally, the trick is to make sure the chocolate doesn't reach that magic 34C, but without careful observation and a very accurate thermometer, this isn't always practical. Shirley Corriher, in her new book BakeWise, suggests going no higher than 43 to 48C, then cooling rapidly to 30C while stirring constantly, and then reheating back to the magic 32C level; if it's done right, a smear on a piece of wax paper should dry shiny and hard like fresh chocolate. Corriher's sources have different approaches -- one, Dr. Paul Dimick of Penn State, uses a bowl of ice water for the cooling, warms it slightly above the cooling temperature, then holds it and reheats to 33C. Corriher herself suggests using a stirring stick made out of the same chocolate you're tempering (the melting pretempered chocolate provides nucleation sites for the desired beta crystals) or simply stirring like crazy while in a walk-in refrigerator. The easy solution, though, is simply to remove most of the cocoa butter and replace it with vegetable oils, either soy and cottonseed (which can be mixed freely with cocoa butter) or with palm kernel oil (which can't because it causes the fats in the mix to precipitate on the surface, a phenomenon known as "bloom"). This material is known as compound chocolate and is a common ingredient in the "melting chocolate" you often see at craft stores. (I have a friend who is a fan of Magic Shell, the topping that you pour onto ice cream that turns into a hardened chocolate shell, like the coating on a Klondike bar. Magic Shell is a particularly unusual form of compound chocolate that takes advantage of coconut and sunflower oils and their high level of saturated fat to congeal almost instantly.)

A slightly more frustrating issue is seizing. Remember that I said chocolate has a starchy component as well; a small amount of moisture in a container of melted chocolate can cause the starch and sugar in the chocolate to glom together in a blob similar to the lumps in pancake batter (if you enjoy fresh-dipped strawberries you've probably had this happen about halfway through your dessert, for example, and seizing starch is at least part of the cause of that nasty burnt foam on an improperly mixed cup of cocoa). Improbably enough, the answer to this is to actually add more liquid; the result will be somewhat limited in its uses (it's terrible as a coating for example) but is fine for glazes, icings, and fillings. In fact, adding a liquid is a fairly common thing -- corn syrup for fudge, cream for ganache -- but in cases where it's done intentionally the chocolate is usually poured into the liquid or melted with it rather than the other way around. (And don't ever add hot chocolate to a cold liquid. If you've ever tried to use melted chocolate to make an ice cream sundae rather than fudge sauce or chocolate syrup, the reason should be obvious.) Incidentally, the starchy bits in chocolate allow pastry chefs to pull something of a culinary fast one in the case of the flourless chocolate cake, which in practice is slightly closer than a souffle than a cake. It's somewhat clearer what's going on in this Epicurious recipe, which uses cocoa powder as well as melted chocolate, than the Martha Stewart recipe in the link, but either way the starch in the chocolate solids performs exactly the same function as flour does in a regular cake, linking up with the eggs to create structure.

I think it's fair to say that as food science subjects go, chocolate is definitely one of the more interesting ones, and chocolate's oddball properties have been the subject of numerous specialized books (including those by Alice Medrich, Marcel Desaulniers, and Elaine Gonzalez). And this article doesn't even go into some of the stranger bits of the manufacturing process like conching (almost like a liquid kneading that smooths out the particulates in chocolate from a pebbly texture to the smooth one we're used to) and Dutch process (treating cocoa powder with alkali to darken it and reduce its acidity). And yet, as fiddly and strange as chocolate really is, who would want to be without it?

Source material

Cook's Illustrated Magazine, Baking Illustrated. Brookline, MA: Boston Common Press, 2003. Though I give recipes from other sources above, their treatment of flourless chocolate cake can be seen as definitive.
Corriher, Shirley, BakeWise. New York: Scribner, 2008, ISBN 978-1416560784. Corriher's sequel to her ultra-authoritative CookWise formed much of the backbone of this entry, and includes not only much of CookWise's original baking wisdom but much other stuff that Corriher has learned over the years of writing the second book. The chocolate material is in Chapter 1, on cakes.

Smith, Jeff, The Frugal Gourmet Cooks American. New York: William Morrow, 1987. Includes a reconstruction of Aztec xocoatl, using chicken broth (in lieu of turkey or guinea pig broth, perhaps?) as the main liquid and Tabasco sauce for the chile spice.

Also, an old National Geographic article that was so far back I can't even remember what decade. Some great pictures of the conching pools at the Hershey facility in Pennsylvania though.