I know you don’t like information from books written by old dead Germans however Kunze gives us some interesting clues here:
3.4.1.6 Thermal exposure of the wort
During boiling, further Maillard products and Strecker aldehydes are formed, tannins oxidized and thus the the thermal exposure of the wort is further increased.
And here we find in this paper..
Impact of Wort Amino Acids on Beer Flavour:
Inês M. Ferreira and Luís F. Guido
these descriptions of the compounds in question.
Strecker Degradation Products
2-methylpropanal - Grainy, varnish, fruity
2-methylbutanal - Almond, apple-like, malty
3-methylbutanal - Malty, chocolate, cherry, almond
Methional - Cooked potatoes, worty
Phenylacetaldehyde - Hyacinth, flowery, roses
Benzaldehyde - Almond, cherry, stone
It certainly looks like the smoking gun.
What percent of the initial volume do you lose during the boil?
Hey Bilsch
Do you know whether there are other pathways for these aldehyde productions by yeast? Or maybe
@Northern_Brewer or
@VikeMan has any insight?
I'm pretty skeptical that it's oxidation or heat stress on my wort and here's why:
I presently have a Scottish export and a marzen, both brewed using the same system, both brewed using the same mash and lauter processes, same yeast handling techniques, same amount of wort oxygenation, same yeast nutrient. I use an electric spike system and boil at 3850 watts every time. (the heating element will run at 100% or 5500 watts until it registers boiling on the PID, so there may be some heat stressing during initial heating to boil.) my boil-off rate is 1.2 gallons per hour.
The marzen has no hint of this almond-like (almond extract, artificial cherry, very slight alcohol warmth) flavor, while the Scottish export is a bomb straight from the fermenter!
The biggest differences between the two recipes are that the marzen obviously used a lager yeast and the Scottish ale used white labs Scottish ale yeast, and the Scottish ale also contained a high percentage of simple sugars (invert and dark brown sugar). I fermented both right at the low end of the respective yeasts' temperature ranges as well, so they should not be throwing excessive esters.
I notice that this flavor seems to occur in beers using English ale yeasts which tend to favor ester production. I've had it most prominently in an irish red, 2 scottish exports, and an english brown ale, and a english strong bitter.
I feel that I'm very strong on cold side oxygen reduction and use a closed process from yeast pitch to a liquid purged keg.
So I suspect that what I'm tasting is one of these aldehydes but I think it has been synthesized from some chemical change to a yeast ester. OR I'm tasting a combination of yeast esters and my brain is simply mistaking the combination for almond-extract (I'm certainly not ruling out that this is simply a sensory/descriptor issue)
Does any of that sound plausible to you?