I am a bit sceptical. Two arguments:
1. If a high amount of those amino acids would lead to more fusel alcohols, this would mean, that at least for clean and nice spirits we shouldn't use natural yeast nutrients, because they are full of those amino acids. Look at nutrition facts about yeast (natural yeast nutrient contains mainly dead yeast). Dry yeast contains for example around 4% leucin and 3% isoleucine. But IMO in reality many nutrients lead to a better and cleaner ferment. This is contradicting. Try it out, two batches, one with and one without dead yeast. Or instead of yeast try eggwhite (BTW, if I ever want to invent a new neutral wash recipe, powdered eggwhite would be one of the ingredients, especially because of the amino acid arginine). I don't think, the one with more amino acids will smell more like fusels. At least the distillate! The wash? I am not sure. Those fusel alcohols have high boiling points (isoamyl alc 131°C, isobutanol 108°C). But some esters also have high boiling points (ethyl butyrate 121°C), but easily come over... perhaps again this graph is interesting:
http://homedistiller.org/forum/download ... &mode=view
Looks like that you need a reflux still to keep isoamyl and isobutanol in the boiler.
But probably I am wrong:
http://scottjanish.com/esters-and-fusel-alcohols/" onclick="window.open(this.href);return false;" rel="nofollow
Interesting detail:
"the levels of esters in the beer fermented with no trub were higher than the beers fermented with the trub added."
"On the other hand, the formation of fusel alcohols slightly increased in beer fermented with high levels of trub."
trub = proteins = amino acids. More amino acids -> more fusel alcohols. But less esters? Strange, because later they write, that yeast nutrient (dead yeast) increases both, fusel and esters:
"The addition of amino acids of valine, leucine, and isoleucine (total nitrogen added = 95 mg/L) was found to strongly increase the production of fusel alcohols (isobutanol, isoamyl alcohol, and amyl alcohol). Specifically, 60-70% of the added leucine and isoleucine were transformed into isoamyl alcohol and amyl alcohol, and the all the valine was transformed into isobutanol."
What the hell is the difference between amino acids of trub and of dead yeast?
2. A typical high ester Rum has still 200 times more ethanol than esters. This means there is only 1g carboxylic acid and 1g esterification-alcohol in one liter 40% Rum. This means only 0.25% of all alcohols (ethanol and fusel alcohols) will build an ester. I know, this calculation has a few flaws, but I think it's good enough to have an idea of the amounts. And now the problem: Even if you manage that your yeast forms many fusel alcohols, only 0.25% of them will turn to an ester. 99.75% will remain stinky fusel alcohols (which come over or not?). Or will the acid prefer the fusel alcohols over the ethanol? I don't know. But to get a nice fruity and not stinky result, the esterification rate of fusel alcohols should be much higher than the rate of ethanol. But actually I am a bit unsure here: I don't know how bad in what amounts each of the fusel alcohols smells. I have propanol here. Of course it doesn't smell yummy, but it's not intense. Probably the flavor of the ester is much stronger than the smell of the fusel alcohols. Like with ethanol and ethanol-esters (ethanol doesn't have a strong smell, but its esters have). Perhaps 0.25% or less esterification is enough to mask the fusel smell with fruity flavors?
But still, for me the chance to get an ethanol-ester looks much higher than the chance to get a fusel-ester. If your esters are 98% ethanol-esters and 2% fusel-esters, will it smell really different than if you have 100% ethanol-esters?
http://scottjanish.com/esters-and-fusel-alcohols/" onclick="window.open(this.href);return false;" rel="nofollow
Yes, it looks like 2% non-ethanol esters makes a difference. Taste thresholds for isoamyl acetate is 20 times lower than for ethyl acetate. Unbelievable, when I think about the intense smell of ethyl acetate. I can't imagine something smelling 20 times more. But the threshold of isoamyl acetate is 40 times lower than of isoamyl alcohol. This means 0.25% esterification is not enough to cover the fusel alcohol smell. It would need 2.5% to notice both equally.
If I am right, the highest chance to get fusel-esters in a dominating amount is in the dunder pit. Because only here it's possible to have more fusel alcohols than ethanol (because fresh dunder contains almost zero ethanol, but probably many fusel alcohols). But the (fusel-) alcohol strength in dunder is very low for a good esterification rate. So when we use the dunder, it will contain much more acids than esters. And the acids will come in contact to the massive amount of ethanol sooner or later and will build ethanol-esters. Or how much could sulphuric acid help here? Perhaps adding sulphuric acid to dunder before adding the dunder to the low wines or wash gives the fusel-alcohols a head start? I don't know how effective the catalyst works under such bad circumstances (low (fusel-) alcohol strength). When trying this out, the dunder should be stored sealed after the sulphuric acid treatment or you will loose esters to the angels.
This is why I am not sure at the moment, if there is a for us useable method for fusel-esters dominating ethanol-esters.
But are the fusel-esters really needed? How many of you have ever tasted a high ester rum? This stuff is expensive. I only one (but often, I have a whole bottle, Habitation Verlier Hampden LROK). For me it smells possible, that almost only ethanol-esters come from the wash and the dunder, mainly ethyl acetate and ethyl butyrate. And then happens much with the oak of course. And probably longer ester chains are formed with time. Perhaps unfortunately it's like always with spirits, you simply have to wait a long time, and then perhaps you don't get exactly what you wanted to get at the beginning, but the quality rises continuously.
