sp0rk wrote:Have a read of Yeast by Chris White, a very informative book on all things yeast
I really like this book so thanks for suggesting it. I've only read about 33% of it so far, the parts which I think are applicable to distilling. Chris White also has some of that work published on his companies website. Like the graph which is relevant to what you stated.
http://www.whitelabs.com/sites/default/ ... e_Line.pdfWhilst there is a lot there that we can take as distillers there is a lot we can't necessarily draw from either. For instance that graph is likely from a beer brew and for a beer brew you want to have the lag phase appropriate for the tastes you are after. The majority of taste (ie esters, fusels) is produced is in the lag phase, that graph shows that ~66% of the diacetyl is. Reduce the lag phase and reduce the diacetyl, along with a tonne of other esters/fusels.
I think this is why the pitch rate for distillers is extremely important, the higher the pitch rate the less yeast growth you get and in theory less flavours produced. There is of course a few important things you need to change in your wash if you do pitch a lot of yeast. ie nutrients.
Since diacetyl boils at 88C, 10C higher than ethanol, in any reflux column it's much easier to strip it out than the alcohols which are very close to ethanol that are more likely to be produced in the autolysis of the yeast in the "resting phase". So personally I don't see much advantage as distillers to care about diacetyl much at all, the smearing of the heads components which have very similar boiling point to ethanol is much worse in my opinion than diacetyl. I think this is why it's prudent for distillers to get that wash and yeast separated as soon as it's done because you're going to stop any reactions from occurring that do occur if you don't. I can't see a reason why you would prefer the potential for less diacetyl.
I also cannot find any real scientific knowledge on when the so called "diacetyl rest" starts and stops. How can the yeast actually do anything when there is no sugar left? Yeast can reduce ethanol but only in the presence of oxygen which shouldn't be there in a finished fermenter. So where is the energy coming from exactly to "clean up" the brew? It seems to me once the CO2 stops there is no way anything can happen in the wash except the death of yeast and the attributable flavours it introduces. This would suggest the so called diacetyl rest can only happen whilst there is something to ferment and that by the end of CO2 activity it can no longer happen in any appreciable way except through autolysis and those resources being reclaimed which also introduce other unwanted flavours.
Personally I think a large problem when it comes to home distilling is there is so much disinformation spread due to people following beer/wine brewing science.