So, the short version of this post is that attempt #2 at tempering milk chocolate worked! The long version, well……tempering chocolate is still a deep, dark mystery to me. The basic idea here is that the fat in chocolate can take (depending on who you talk to) five or six crystalline structures, all of which have different properties. The types, I-IV, increase in stability and melting point as you move up the scale. Type I crystals, for example, melt at 17.3C (63F), and are only stable enough to exist for a few minutes before migrating to Type II crystals, which mely at a higher point. All chocolate is, to some degree, doing this crystalline morphing until it hits the Type VI crystal, which melts at 97F, and has a waxy mouthfeel. Tempering attempts to convert the majority of the crystals in the chocolate to Type V crystals, which melt just below body temperature, are stable enough to stick around for months, and contract when cooled. This contraction makes it possible to mold chocolate and extract it from the mold.
This sounds simple, but there are a number of complicating factors, none of which I completely understand yet. First, most chocolate, even when it seems solid, in fact has a lot of liquid chocolate trapped in the fat matrix. You want to keep some of this liquid chocolate around, or otherwise you end up with “overtempered” chocolate. Second, the size of the crystals in this matrix determine if you get shiny chocolate or not. Crystal size is determined by how you treat the chocolate after tempering. Cool it too fast, and you can get bloom. Cool it too slowly, you get big crystals and no shininess. Third, the surface that it is cooling in makes a difference. Cool it against glass or plastic and you get a smooth, shiny surface. A rough surface will eliminate shine.
So, the last batch of chocolate I made was a milk chocolate, which complicates this even further by introducing milk fat into the mix, which interferes with crystallization (making the chocolate soft, which is good.) Tempering milk chocolate requires working a few degrees cooler than working dark chocolate. My first attempt to temper this chocolate resulted in this:
The chocolate has no shine at all, is soft at room temperature, and has a sandy texture you can see on the breaks. I was working on too warm a surface, so the needed seed crystals never formed. Interestingly enough, chocolate can be shiny and not bloomed even when it’s not tempered. Here’s some chocolate from the exact same batch, poured directly into a Pyrex dish from the melangeur and cooled at room temperature for a day. The dents are my fingerprints, showing that this chocolate is soft and melts well below body temperature. However, note that it has a good shine, and after a day, is showing no signs of bloom. I have no idea what crystal forms are present here.
At 120F, we’ve melted all of the crystal forms and can start again. The poor initial temper hasn’t damaged the chocolate at all. Here’s what that dull, untempered chocolate looks like when remelted. It’s a nice, thick, shiny chocolate. (And, as my wife will attest, quite tasty!)
Working with a slightly chilled stone (about 70F), I was able to create some good seed crystals and get the whole mass tempered using the mush method. After cooling overnight, here’s the result:
It’s somewhat shinier, though i cooled this in a pan lined with parchment paper, so the surface is somewhat rough. I also made the mistake of putting it in the freezer for a few minutes as it was setting up, causing instant streaking on the surface from overly rapid cooling. (Note to chocolatiers: rapid cooling produces an actually quite pleasant wood-grain looking set of streaks through the chocolate. This could conceivably be used to intentionally create a rather nice, although unconventional, look on some chocolates.) However, this has a uniform texture and set up quickly. It’s tempered, but it’s not a great job.
In contrast, here’s an untempered piece that was slowly cooled in the refrigerator on a smooth plastic surface. It’s got a nice shine to it. Next batch, I just need to get the proper tempering technique together with the proper cooling technique.
Also, clearly I need to be doing more library work on exactly how the liquid and solid phases of the chocolate are interacting, and generally getting a better framework for thinking about the multiple processes going on here. (Yes, I could buy a tempering machine, but every chocolatier I talk to insists that having a complete understanding of tempering is critical, if for no other reason than debugging things that go wrong, and judging how to improve results.)