Esters Production in Low vs High Nutrient Ciders

[AW]

Hey All,

I am writing my own short review on ester production in cider, but I'm having some trouble accessing a few resources.  Does anyone have a copy of the papers below for research purposes?

Tarko et al 2021 - How keeving determines oenological parameters and concentration of volatile compounds in ciders? Journal of Food Composition and Analysis, Volume 100, 2021, 103897

Rosend et al 2021

The Effect of Cidermaking Practices on Ester Production by Yeast. Tallinn University of Technology, 2021.

Volatile Compounds Formation in Cider
By Aline Alberti, Alessandro Nogueira
Volatile Compounds Formation in Specialty Beverages

If anyone has a bibliography on keeving longer than 3-5 peer reviewed references...can you share?

There are a couple loose ends I'm still investigating...and I would love to get clued in to new ideas if anyone has any. 

(1)  The explanation in Villere et al 2015 for the increase in acetate esters in keeved ciders is overproduction of acetyl coA.  Some experiments have supported this hypothesis, but other research seems to indicate that enzyme activity and not substrate concentration  is the limiting factor in acetate-ester production. 
More recently, the mitochondrial Eat1 enzyme has been discovered in yeast that produces short chain acetate-esters, and probably is expressed as a stress response.  
Are there any other hypothesis to explain the benefit of keeving (or at least it lack of detriment) on ester production?

(2)  I'm struggling slightly with the use of Andrew's term "unclarified" in his chapter on Cidermaking in "Fermented Beverage Production".  From my reading, it seems that some esters are difficult to produce in a "low nutrient" strategy, namely the C5 branched-chain esters and maybe the phenylalanine-based esters.  Is the word "unclarified" to warn against excessive clarification of the must?  Is that reason indeed linked to production of these specific esters....or some other reason like the general danger of sticking fermentation too early?    

Thank for any discussion you guys can provide...Cheers!

[Andrew Lea]

I can answer one of AW’s questions specifically.

Way back in the 1960’s there was much debate and research on whether greater aroma was produced by unclarified (filtered) fermentations or not.  This was reviewed by Beech in 1993 in his chapter Yeast in Cider Making and in other places   I attach the scan of a paragraph which is relevant. Anyway by my days at Long Ashton in the 70’s this was pretty much received wisdom and so I pretty much fell into line when I was writing. 

If you want to look at the primary data you will need to spend some time in a university library or online.  I am long retired and don’t have this sort of info available.

Just a word of warning. Clarification by keeving isn’t the same thing as clarification by filters which became popular 50 years ago and is again not the same as clarification by membranes. 

Andrew