Sour Yeast Strain.

Ester production...

 

Initial ester production or esterification/transesterification?

 

One leads to the other right? A warm fermented lager will most likely have a decent amount of esters going into secondary I would think??

 

Read for some chemistry?

In order for sulfur to be a part of ester production, you need to make a thioester, which is the combination of an acid, probably derived from acetyl Co-A, and a thiol, which is the sulfur containing molecule. However, in order for you to this you need two things. You need a way to make the sulfur based amino acid (most likely cysteine, but glutathione, a tripeptide, is also a common participant) cleave from the rest of the conjugated precursor molecule and then join with the carboxylic acid to make the thioester. This just doesn't happen on its own, you need two families of enzymes to make this happen. The cleavage (hehehe) of the s-cysteine conjugate requires carbon sulfur lyase, an enzyme that is not common in the yeast that we use, and then you need powerful esterase enzymes, like those present in most Brettanomyces species.

Long story short, this process would not use free sulfur, sulfites, sulfates, or H2S. It would involve bound sulfur in the form of sulfurous amino acids or peptides, which would, very probably, come from late addition hops or dry hops, which aren't very common in sour beer production.

For what it's worth, this could also happen later in the fermentation process, as hydrolysis of esters is an equilibrium reaction (i.e. esters get formed and destroyed until they reach a balanced equation, more or less) and the esterase enzymes could use the conjugate molecules to make additional thioesters. This situation, however, is less likely to produce the amount of thioesters that the first one would, because it would not be happening during the logarithmic phase of the yeast's life cycle and they would be less enzymatically active.

Make sense?

 

Sure

 

After leading through American Sour Beers for the upteenth time this AM I also noticed that Ithaca brewing primary ferments their mixed/sour beers with their house ale strain (007) at high temps then crash cools mid fermentation to promote diacetyl.

“the fermentation temperature is allowed to freeride to around 90 to encourage a fruitier profile. Once the desired gravity is reached, 1.028-1.032 the beer is crash cooled. This rapid chilling mid fermentation causes VDKs (e.g., diacetyl ) to remain in the wort, which O’Neil values as additional substrate Brettanomyces flavor development.”

Might have to try the D-bomb route next go around to see what happens.

 

I would certainly love to hear your results, but there is no science to this. Brettanomyces doesn't transform diacetyl into anything except acetoin.

The whole "Brettanomyces transforms off-flavors into good ones" is a complete fallacy, as well. Brett sp. are just yeast. Even though their esterase enzymes are strong, they're not magic. The thought that they'll completely transform foul smelling stuff like butyric acid and isovaleric acid into their wonderful smelling counterparts ethyl butyrate and ethyl isovalerate just isn't accurate. They'll esterify a certain amount, but by no means "all" of those chemicals. Some great reading about the capabilities of Brettanomyces can be found here. The ester production section is linked for continuity's sake.