At what stage to add lecithin
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Tech Help, Tips, Tricks, Techniques
Only have a few moments now i'm afraid, not much time to get into it.
Lecithin is an ampiphillic emulsifier - one end of it is hydrophillic (attracted to water), end end is lipophillic (attracted to fat). One of the (many) reasons chocolate can get thick is as Mark notes, there is a small amount of moisture present - sugar carries a monolayer of moisture with it, milk has some adsorbed to it's protein, lactose has water of crystallization, etc. Where that moisture comes into contact with, say, sugar you get a phase transition (your sugar goes from crystalline to solution - forms a syrup), and anyone who's ever spilled a soda and missed a spot in cleaning it up knows well that it can get sticky as all get out. The hydrophillic end of lecithin will, essentially, 'stick' to that syrup phase, whereas the other end of lecithin will 'stick' to the cocoa butter (a bit more complicated than that but you get the jist) forming a bridge between the two, essentially making it less sticky.
Now, conching generates (or can, dependent on your process) a lot of heat, and some of the moisture can be volatilized off during conching - so if you've got a process that does this, adding lecithin too early may tie up the moisture, making it harder for it to go away. However, not all processes blow off moisture very well, so it's good to know your process. Some processes get hot enough that you hit what's called the glass transition point of a crystal (sugar), and you can shift it from a crystal to an amorphous state (glass). Amorphous sugars like to collect ambient moisture.
Afraid i've never looked at hardness as a function of lecithin. My gut tells me that the more lecithin you use the softer your chocolate gets (by just a tad) as lecithin is 50% fluid oil, but again i've no direct experience measuring it and as such don't know for certain.