When I make (chicken) stock, after it's made and the fat skimmed off I reduce it 3-x and freeze the resulting highly concentrated stock in cubes. Obviously I would prefer the reduced stock to be as flavoursome as possible. I only need to do this every 2-3 months, so I don't care that much how long it takes.

I generally do this at a temperature of maybe 80 degrees C, but it occurs to me that it's not at all obvious this is best. I think the considerations are:

  • Faster and hotter means a higher ratio of water evaporation to more-volatile-things evaporation. The things that give the stock flavour are mostly more volatile than water -- they have to be, to get to your nose when you eat -- so (perhaps counterintuitively) I would expect that for a given amount of water removal you lose less flavour by doing it faster.
  • Faster and hotter might mean that some (probably undesirable?) chemical reactions can happen that simply wouldn't have happened at a lower temperature. The actual stock-making has happened at about 85-90 degrees C so I guess the question is whether anything bad starts happening between that and 100 degrees C.
  • If you actually boil the stock (which of course folklore says not to do) then there are the mechanical effects which may make the stock cloudier if there's still some fat and stuff in it. (I don't really care whether it's cloudy.) Maybe there are other relevant differences between boiling and not-quite-boiling; trying to think about the physics of it I think probably not, but not with any confidence.
  • Maybe other things?

Is there a known right answer here? (Scientific studies of VOC content after reducing at different temperatures? Known universal practice at fancy restaurants? Semi-scientific experiments by chefs, food journalists, hobbyists?)

A few questions I've looked at, which are relevant but don't really answer my question:


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