Alternative to keeving? From 1935....

[jeff.k...@gmail.com]

Hi folks

I've been reading a few old cider references.  In Charley (1935) "The biochemist in the cider factory" available here:

https://ur.booksc.eu/book/51863421/a2b434

there is an interesting idea I have not seen elsewhere.  On p.66 we can read:

"A method has been developed in France in which the fresh juice is collected in a shallow vessel which exposes a large surface of the juice to the air.  Under these aerobic conditions the yeasts propagate at a fast rate, but their fermentive capacity is repressed.  The yeasts assimilate nitrogen and when a heavy crop of yeasts is formed the juice is racked to a vat for fermentation; the juice now contains only depleted resources of nitrogen and the yeast action is correspondingly retarded."

I do wonder how the "fermentive capacity" can be retarded if the yeast propagates quickly.  Has anyone tried anything like this?  If is works, it could be an alternative to keeving in musts that otherwise are not suited to keeving.

If the idea is just to keep the must oxygenated, you should be able to set up a bubbler in an existing fermentation vessel rather than find shallow vessels.

Just thought I would share.  Seems interesting.  Old literature has some cool stuff in it sometimes.  

/Jeff

[Eric Tyira]

Never heard of it but it sounds like the yeasts use up the nitrogen for the purpose of mass/rapid replication.  I guess they think there's a massive amount of juice given the large surface area.  That juice is now nitrogen depleted and racked into a standard tank for limited fermentation.

Sounds like the same general concept of removing what the yeasts need to do their job and then adding back only what is needed for them to do their job.  I'm guessing the wild yeast are more tolerant of such stressed conditions as compared to the commercial yeasts which are more fussy (need proper nutrition to avoid h2s formation)?

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[Claude Jolicoeur]

Le vendredi 15 avril 2022 à 05:40:49 UTC-4, jeff.k...@gmail.com a écrit :

"A method has been developed in France in which the fresh juice is collected in a shallow vessel which exposes a large surface of the juice to the air.  Under these aerobic conditions the yeasts propagate at a fast rate, but their fermentive capacity is repressed.  The yeasts assimilate nitrogen and when a heavy crop of yeasts is formed the juice is racked to a vat for fermentation; the juice now contains only depleted resources of nitrogen and the yeast action is correspondingly retarded."

The important (and unanswered) question here is "What does the author mean by shallow"?

If he means somewhere between 40 and 80 cm of liquid height, then this corresponds to what I routinely do the the cuvées that I don't keeve, with a yeast growth in a pail (with good air contact) followed by a rapid racking towards a carboy as soon as the froth is down. And in effect, as long as there is not excessive natural nutrients in the juice, it becomes possible to reduce the speed of fermentation and stop it with some remaining residual sugar.

And in effect, 50 cm of liquid height could be considered as shallow compared to the size of typical fermentation vats of the time which could be 2 or more meters high.

[jeff.k...@gmail.com]

I'm going to resurrect this thread because I just stumbled across this: https://en.wikipedia.org/wiki/Pasteur_effect

This is obviously settled science (since Louis Pasteur's time, for crying out loud!) but it was still news to me.   It also confirms the observations in the 1935 paper I mentioned in the original post two years ago.  Apparently, when yeast are exposed to oxygen, it inhibits ethanol fermentation but boosts yeast propagation.  This should have similar applications as keeving.  

I'm wondering if aerating must immediately after pressing would boost yeast cell counts and reduce YAN in solution.  Since little alcohol has been produced, presumably oxidation will be less of a problem?  If we can boost yeast propagation but limit ethanol production, then a first racking ought to be particularly effective at reducing available nitrogen.

Maybe the risk of oxidation is just too high even early in the fermentation.  Still interesting!

/J

[AW]

This is a very interesting topic.  I'm not sure the "Pasteur effect" (inhibition of glycolysis by oxygen) is at play here.  Rather, the "Crabtree effect" (inhibition of electron transport chain by glucose).  

If I'm not mistaken, the Pasteur effect would be operative at low sugar concentrations (at or below around 2%).  In that case the presence of oxygen would shift yeast metabolism toward respirations, which slows flux through glycolysis.  Whereas at the high sugar concentrations found in fresh juice, oxygen is used for some obscure anabolic reactions but not as an electron sink for main-trunk metabolism.  

My biochemical interpretation of the 1935 language is that high dO2 stimulates yeast shift carbon flux more toward building biomass.  This would match the observation of high nitrogen consumption AND the observation of diminished ethanol production (relative to sugar consumption).