Help on Ester Production

[Marktic]

Hoping someone can shed some light on factors affecting ester production.

As I understand it...an ester is formed upon a reaction between an alcohol, a fatty acid, and acetyl coenzyme A. Esters are linked with lipid synthesis. During strong yeast growth, the acetyl CoA pool is being used up in creating new cells, and is not available to produce esters at any significant level. Ester production peaks at the cessation of lipid synthesis, as any unused acetyl CoA would now take place in reactions forming esters.

So, for instance, adding a sufficient amount of oxygen to freshly cooled wort stimulates yeast growth and lipid synthesis, and hence lower ester levels.

Now where this starts to get fuzzy, is regarding temperature. A higher temperature would stimulate yeast growth...which would theoretically reduce esters according to the above, but this is obviously not the case. More fusel alcohols would be produced at higher temps, leading to increased levels of certain esters, but elevated temperatures increase ethanol based esters as well.

And the whole underpitching/overpitching thing...how does that tie in to this?

What is the science behind this all???

 

[divrack]

science? pff. what's science ever done for us? name one thing.

 

[Smellyglove]

You can dive down into some reasearch from what you get from my post here

 

[Marktic]

Thanks so much! Alcohol Acetate Transferase (AAT) was the answer.

After a little research...AAT, is stimulated by strong yeast growth and is responsible for the acetate esters in beer. It sounds like different yeast strains will express AAT in differing amounts, such as in a hefeweizen yeast vs an american wheat beer yeast, regarding their creation of isoamyl acetate. Interesting stuff.

 

[Smellyglove]

Thanks so much! Alcohol Acetate Transferase (AAT) was the answer.

After a little research...AAT, is stimulated by strong yeast growth and is responsible for the acetate esters in beer. It sounds like different yeast strains will express AAT in differing amounts, such as in a hefeweizen yeast vs an american wheat beer yeast, regarding their creation of isoamyl acetate. Interesting stuff.

Don't forget about ethyl acetate, which is a giant when it comes to esters.