Nutrient reduction

[Erik Nilsson]

Hello,

As an alternative to Keeving, I understand that multiple rackings can be used for achieving nitrogen depletion and residual sweetness. However, this reportedly does not work with high-nitrogen must. I am wondering why that is the case and if it can be remedied somehow. It would be interesting to try this strategy next year for getting a sweet cider, but I'm using garden-grown apples that I suppose have medium to high nitrogen levels.

The method has been discussed  here https://groups.google.com/g/cider-workshop/c/0rM5X7fp14I/m/hp7FcBMMAgAJ and here https://groups.google.com/g/cider-workshop/c/XWihX0w2hPo, with an interesting historical note from Patrick.

From what I read, apple must usually has nitrogen content of 30-150 mg/L. About 90% of this is assimilated by the yeast during proliferation phase, ie the first few days. From some studies, it seems that a nitrogen level of 300 mg/L or more is needed to leave some residual nitrogen, and I suppose that would make this strategy of depletion fail.

This made me wonder if nitrogen depletion of higher nitrogen must would be possible if one could achieve a large enough yeast population that can assimilate more nitrogen. Im not sure which factor is limiting the maximum yeast population in must, but glucose and nitrogen seems unlikely candidates in this scenario (since glucose is still quite high when the yeast goes into stationary phase). Maybe it is oxygen (sterols dilution and such limiting the number of cell divisions that can take place in anaerobic conditions)?

This discussion suggests that oxygenation (by using shallow fermentation vessels) could increase final yeast cell density in the must: https://groups.google.com/g/cider-workshop/c/esjLYScqQWg

So my question after all this long-winded thinking is: Would oxygenation (eg using a bubbler or stirring for 24-48 hours after pitching) enable a larger nitrogen removal by allowing a larger yeast population density?

Cheers,

Erik

[Claude Jolicoeur]

Hummm, that would make a nice research project for a Ph.D. thesis on the subject of fermentation dynamics!

Bear in mind that as you increase the yeast population to consume all the free N, this will also make the speed of fermentation increase in the same proportion, and you might reach dryness before you have time to rack!

Also racking will only remove the yeast cells (dead and alive) that are on the bottom of the vessel. All cells that are in suspension in the fermenting cider will remain after racking.

[Patrick McCauley]

Hey Erik. This sounds way beyond my pay grade, but I think that the point of the multiple rackings is to not only reduce the the nutrient load in the cider, but to also reduce the amount of yeast in the cider. When you're racking at low temps, many of the yeast cells will settle out and really slow the fermentation speed down. I also highly recommend the debourbage at the beginning. I sulfite, and let mine settle at cold temps(the colder the better) for a week or more before racking into the fermenters. Multiple rackings alone can work, but the settling helps immeasurably, in my experience. Good luck!

Pat McCauley

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[Erik Nilsson]

Indeed! Its a pity I did mine on kidneys. Thanks for the advice on speed, that's a good point. Perhaps slowing things down by lowering temperature might make it easier to time the racking.

There seems to be some studies (in wine) showing that agitation/stirring (perhaps partly through oxygenation) increases cell counts and assimilation of nitrogen (https://onlinelibrary.wiley.com/doi/full/10.1111/ajgw.12338), and as you point out also increases fermentation speed. It seems to be possible to increase cell counts by 30-50% and to double nitrogen assimilation percentage.

As for effectiveness of racking, that's also a good point that any assimilation of nitrogen into yeast also needs to be removed efficiently. As Patrick and yourself pointed out, pre-fermentation clarification (eg by debourbage, lower temp, pectinase) would increase the sedimentation of yeast cells so that a larger proportion can be removed by racking.

It seems at least theoretically possible that initial oxygenation could increase nitrogen removal by a meaningful amount and perhaps increase the chances of getting residual sugar in a relatively high nitrogen must.

Best wishes,

Erik

[Erik Nilsson]

Thanks, that is great advice! Im thinking that low temp is good for many reasons in this context. About debourbage, does it change the flavor of the cider? Naively, I would think that maybe removing solids too early might giva a thinner taste, but I really have no idea if that is the case.

Kind regards,

Erik

[Bartek Knapek]

My experience with slowing down fermentations by multiple racking is that is works best witha juice that is cleaned-up first - basically add enzyme and wait some 12-24h for the sediment the fall. Warming up the juice to 40-50C initially helps to accelerate that. Byt this you are getting rid of majority of small particles floating in the juice, that yeast would otherwise stick to and not fall. It is also important not to let the fermentation accelerate, as once it does, the yeast will be continuously agitated by CO2 and the rackings will not remove much. So I would not try to encourage growth, rather keep it slow and cool, and rather do more rackings. I do not think with home-garden-grown apples you are getting seriously high N levels. The 300+ mg/L levels are found in intensive orchards, where trees are pushed for growth by high nutrition, both into the ground and into leafs. My garden apples are low in N (judging by relatively slow ferments comparing to commercial apples), despite I fertilize grass around the trees 2-3 times a year. Excessive oxygenation does not sound good to me - it is likely to have side-effects in lowering tannin levels, etc.

cheers //Bartek

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[Erik Nilsson]

Thanks Bartek! That's great information to have and it makes me think I could try this without any shenanigans first. Im curious about your recommendation of higher temperature for accelerating sedimentation. I thought in general lower temp was better for that? Or is it for pectinase activity just in the beginning? (I have wondered about what the optimal temp is for pectinase)

Your point about CO2-agitation is a good one. I was thinking it might be an advantage, since agitation seems to increase nitrogen assimilation, but as you say it would also make removal of yeast by racking less efficient. 

The effect of oxygen on tannin seems complicated, but I see there is a risk of adverse effects there. It seems to differ depending on if its done before or during fermentation: "Must oxygenation in most cases contributed to the reduction of polyphenol content and to the antioxidant activity of ciders, especially when fermented using wild yeast. The oxygenation of musts before fermentation caused an increase in the content of esters and alcohols in ciders. However, the oxygenation of musts during fermentation reduced the concentration of these volatile components." From https://www.mdpi.com/2218-273X/10/6/890.

Best wishes,

Erik

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

Claude, on the subject of fermentation dynamics: do you think there is a relationship between the fermentation temperature and the metabolic behaviour of the yeast?

My (subjective) observation is that the rate of yeast propagation and the rate of alcohol generation are not necessarily connected.  Do you know if there has been any research looking into this?

/Jeff

[Bartek Knapek]

Warming up to 40-50C is for the enzyme to work faster, it came actually as a recommendation on one of the enzyme products that I used. I heat once and then leave for 12-24 to cool down and drop sediment. Works really well. And it does not kill the yeast - still possible to wild ferment after that, if you wish.

cheers // Bartek

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[Erik Nilsson]

Thanks, thats good to know. I actually waited for the must to cool to 37C when I had done pasteurization on a batch, because i didnt know if the heat would inactivate the enzyme. Thanks!

[Stephen Buffington]

Erik, the sound of high yeast count and low nitrogen makes me uneasy. Your chances of minor to serious fermentation flaws in this oxygen rich environment seem high at ambient temperature.

Again low temperature could allow this to work, with the fermentation going slow enough for yeast to recycle and scavenge what they need. 

Stephen Buffington

Shawnee Hill Farm

206.941.6353

On Nov 26, 2024, at 10:40 AM, Bartek Knapek <cy...@knapek.pl> wrote:



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[Erik Nilsson]

If I may comment, Figure 1 in this paper shows the dynamics of cell counts, fermentation rate and ethanol production: https://academic.oup.com/femsyr/article/15/7/fov067/640707

Best,

Erik

[Erik Nilsson]

Stephen, thanks for the warning. I hear you, but do you mean lack of other nutrients than nitrogen (eg thiamine, magnesium, sulphur) would cause flaws if yeast counts are higher? Low nitrogen in itself should not be a problem, since that is the fundamental aim of the depletion/racking strategy as I understand it. Even if going for low temp, the yeast would not be allowed to recycle very much. On the contrary, they would be removed as soon as possible by racking. But this must be the case also for the normal multiple racking method?

Sorry for being a bit obtuse about this. I would actually assume that initial oxygenation is probably not a good idea, since it does not seem to be much used in cider making (with the exception of that "Chemist in the cider factory" paper referenced by Patrick maybe), but it might be fun to try on a small batch to compare eg the effect on final gravity. It is anyway fun to think and learn a bit about fermentation dynamics.

Cheers,

Erik

[Claude Jolicoeur]

Le mardi 26 novembre 2024 à 13:15:27 UTC-5, jeff.k...@gmail.com a écrit :

Claude, on the subject of fermentation dynamics: do you think there is a relationship between the fermentation temperature and the metabolic behaviour of the yeast?

Jeff, I am not too sure what precisely you mean by metabolic behaviour, but for sure, speed of fermentation does increase with higher temperature (up to a limit obviously). Also yeast multiplication would also increase at higher T.

[Erik Nilsson]

Hello again Patrick,

A thought on debourbage. I was thinking about how reducing solids could affect things and stumbled upon this (from winemaking):  

"It should be noted that with lower turbidity juice, addition of oxygen at the end of the yeast growth phase can compensate for lack of lipids in the juice, with the yeast able to use the oxygen to synthesise lipids." 

From: https://www.awri.com.au/industry_support/winemaking_resources/winemaking-practices/winemaking-treatment-varying-grape-solids-in-white-wine-fermentation/

..so incidentally oxygenation might actually be beneficial when doing debourbage.

Best wishes,

Erik

[gareth chapman]

I think Claude pretty much summed up the issues in his first post.
High nutrient juice will ferment more readily and quicker, if the fermentation is too quick and turbulent then you won't get enough sediment to rack off of to actually be removing anything worthwhile. Some fruit will just be impossible to slow down,. Later fruit combined with lower temperatures will give you a better chance.
If a fermentation starts within a day or two I generally discount it for multiple rackings.
The reality is that with the availability of PME being pretty much universal now, keeving is your most reliable option.

[Patrick McCauley]

Perhaps this is why I always have a nice settling/clarification after racking, and there is a nice deposit of lees. Could part of that be the introduction of oxygen? I had always assumed that the reduction in biomass and nutrients caused the yeast to drop out. Not sure. Thanks for sharing.

Pat McCauley

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

Sorry, that was not clearly written.

Yes, the temperature impacts the speed of fermentation and yeast multiplication.  What I am curious about is whether the rates of those two parameters as a function of temperature are linked.

For example:

At 20 degrees C, we perhaps see yeast multiplication of X cells/hour and a speed of fermentation of Y FSU.

At 5 degrees C, will those two parameters then be X/5 and Y/5 ( for example)?  Or will you see a situation where you get X/2 and Y/5?  In other words, does the temperature impact yeast propagation and ethanol metabolism equally? 

/Jeff

[Claude Jolicoeur]

Le jeudi 28 novembre 2024 à 06:39:48 UTC-5, jeff.k...@gmail.com a écrit :

At 5 degrees C, will those two parameters then be X/5 and Y/5 ( for example)?  Or will you see a situation where you get X/2 and Y/5?  In other words, does the temperature impact yeast propagation and ethanol metabolism equally? 

I doubt it would be so simple... All I have found is a general rue of thumb for linking speed of fermentation to temperature that I have written in my book, but I don't know how good really this relation is, nor do I know its limits of validity.

For yeast propagation, I really don't know.

[Erik Nilsson]

Fermentation of glucose to alcohol seems to increase with temp up to 40C but yeast growth rate only up to about 30C. So there seems to be some differential effect of temperature on proliferation vs alcohol-fermentation.

"It is shown that the fermentation coefficient increases steadily up to 40° C. (104° F.), after which it falls away steeply. The growth coefficient increases steadily up to 30° C, after which it increases only slightly up to 36° C. and then fells off steeply. The yeast yield calculated on total sugar used diminishes with increasing temperatures of growth, particularly with temperatures in excess of 36° C. (96° P.)." [From https://onlinelibrary.wiley.com/doi/abs/10.1002/j.2050-0416.1951.tb01628.x]

This paper shows that yield per nitrogen is decreased at lower temp (ie opposite that of yield per glucose): https://pmc.ncbi.nlm.nih.gov/articles/PMC2570279/. So lower temp might give more nitrogen assimilation per yeast cell grown.

Kind regards,

Erik

[AW]

Exogenous sterols can be added if indeed sterols are limiting.  I suspect oxygen is utilized in some other obscure non-respiration pathways but I doubt that oxygen as such is limiting here.  I would go forward with sterols/tween rather than risking other kinds of oxidation.  

[AW]

I think fundamentally you want to increase the ratio of N consumed:EtOH produced, so you run out of N before you run out of sugar.  In other words to shift carbon flux away from glycolysis toward protein synthesis specifically.  

Racking intuitively seems like a way to do this but I'm not sure it works exactly that way.  If there was some was of increasing the rate of natural protein degradation....then presumably the yeast would have to burn more N to maintain their proteomes.   

[Erik Nilsson]

Thanks Adam! I see that some beer folks just add olive oil for phytosterols and I suppose that could be a way to compensate lipids lost after debourbage. Yes, increasing nitrogen consumption relative to glucose fermentation to ethanol is in essence what this is about, if by consumption one also includes subsequent removal by racking. It seems that lower temperature would have that effect you suggest, shifting the yeast towards using more of the nitrogen for proteins and such. Though since lower temp also would slow down proliferation I dont know how it all would come together and if it would in the end lead to more efficient nitrogen removal. As intuited by Claude, fermentation vigour and probably other dynamics might limit the usefulness of these ideas. Cudos also to Gareth for pointing that out. Keeving would indeed be a great option, but for myself there are some practical hurdles, like keeping low enough temperature, and it seems a bit difficult to get it working consistently, so other options would be nice to have.

Thanks everyone for the interesting comments. Its a great thing about this forum that there is room for both theoretical speculation and great practical advice from people who know the craft!

If I may summarize a bit what has been said, just to sum things up if someone has similar ideas:

- My starting point was that multiple rackings is a way to remove nitrogen and thereby stop fermentation with residual sugar. This is described in Claudes book (which I finally got today!).

- An obstacle may be medium to high nitrogen content in "lawn-grown apples", though Bartek noted that was not really a problem in his experience.

- The paper referred to by Patrick mentioned a French method of aereating the must to get higher cell counts and thereby remove more nitrogen:

"A method has been developed in France in which the fresh juice is collected in a shallow vessel hich exposes a large surface of juice to the
air. Under these aerobic conditions the yeasts propagate at a fast rate, but their fermentative 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."

 [https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.1935.tb05570.x]

- I suggested aereation (eg with a bubbler) during the first 24-48 hours might have a similar effect. Some concern about unwanted effects of oxygen was expressed.

- It was pointed out that a requirement for this to work is also efficient yeast removal when racking, which is dependent on a high sedimentation ratio. This ratio can in turn be improved by removing solids (eg by debourbage before fermentation like Patrick is doing) and would be decreased if fermentation becomes to vigourous.

In conclusion, I would say based on theory and some empirical basis that this might actually be worth at least an attempt. So when I get the chance (probably next year since my apple stash is getting thin) I'd be happy to compare an oxygenated batch with a non-oxygenated one and see if i can get the final gravity a bit higher by doing some initial aereation. Timing of aereation and racking is probably essential.

Thanks again for all the valuable input!