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So this question challenges a lot Brewers assumption that yeast needs oxygen to reproduce. It just plain doesn’t. Yeast does use oxygen, but it’s a mighty and inaccurate over simplification to say it has anything to do with reproduction. Please don’t answer that I am wrong. There is plenty of scientific studies (including in beverage studies) that you can read to learn about how yeast do not respire when in the presence of sugar, and how they multiply just as well in anaerobic environments.

What yeast do use oxygen for is to produce sterols (basically fat) to more easily take in sugar and in turn excrete alcohol. It has been suggested that adding yeast hulls at the beginning of a ferment will supply the yeast with the sterols they need. This is sometimes done to get stuck fermentation’s going again, because often they get stuck because the yeast have used up all their sterols. Resupplying sterols gets them going again.

So I am wondering what results people ha e had supplying yeast hulls at the beginning of a ferment rather than aerating or oxygenating their brews.

You see some fruit produce some really off flavors when allowed to oxidize, most notably strawberry and watermelon. I want to see if yeast Hull supplication can produce a better product.

Thanks

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    Adding yeast hulls to a stuck fermentation works because the hulls reduce the concentration of fatty acids (by absorption). Fatty acids inhibit fermentation at larger concentrations as they accumulate in the yeast cell wall. Ref: extension.iastate.edu/wine/problem-fermentation-and-yeast-hulls . Do you have any references about yeast hulls creating/containing sterols? – Kingsley Sep 9 '19 at 1:43
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    Found a reference supporting the increase of sterols with addition of yeast hulls to a ferment - ncbi.nlm.nih.gov/pmc/articles/PMC202904/pdf/aem00099-0248.pdf – Kingsley Sep 9 '19 at 1:52
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    As an aside the addition or lack of oxygenation does have an impact of ester formation. Yes its not the only one but oxygenation itself does have other impacts that supporting sterol formation. Its one of many handles you can pull to try and effect the flavor profile one is looking for in the final products. – brewchez Sep 9 '19 at 13:30
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    @brewchez well yes that is correct. In the case of apple cider or wine (and I assume cyser as well) oxidation of the fruit prior to fermentation has a positive affect on the flavor. In the case of strawberry and watermelon, it has deleterious effects making the wine taste like it was flavored with candy rather than fruit. I wasn’t presuming that avoiding aeration/oxygenation is good to everything. – Escoce Sep 9 '19 at 14:43
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Not to supply sterols(that I know of), I was at Plumpton College Wine Dept. in the UK last week visiting an old friend, and they use yeast hulls to supply FAN and other nutrients to the yeast, I did not ask specifically about sterols.

======= Update ====

Yes, they can/do supply sterols, as well as FAN for growing yeast.

Also Olive oil can be used to supply sterols to yeast in the growth phase without requireing oxygenation[https://www.kotmf.com/articles/oliveoil.pdf].

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