4 replies to this topic

[neddles]

So why do we do it? We are told O2 is unnecessary when using dried yeast in beer worts because the dried yeast have already produced the sterols necessary for reproduction.I may be answering my own question but is it simply a matter of the higher OG of the must requiring more growth? Wouldn't pitching more yeast make up for this. Anyone know anything definitive on this?

[neddles]

High OG mainly, also nutrients are lower. Adding more yeast will result in over pitching off flavours.

When I said pitching more yeast I just meant for example 10g@ OG 1.125 vs. 5g@ OG 1.075.

I don't add O2 myself, FWIW.

Interesting. Do you aerate and degas early on in the fermentation?

[Genesee Ted]

With dry yeast, skip the O2 or aeration. Not needed.

[Genesee Ted]

I am not a scientist, so take it for what you will, but dry yeast has already been put through its aerobic phase. If you repitch for another fermentation, then yeah, hit it with O2. According to the data sheets we get at work from the yeast companies, they say O2 is unnecessary and perhaps even detrimental to the final product. Granted, this is for malt based fermentation, not honey or wine musts, but I don't know why it would be different.

[MtnBrewer]

I am not a scientist, so take it for what you will, but dry yeast has already been put through its aerobic phase. If you repitch for another fermentation, then yeah, hit it with O2.

The phase that a yeast is in is more related to the environment it's in than what the yeast has experienced in the past. Yeast don't remember that they've already been through the aerobic phase (which is an oversimplification anyway). Put them in an O2-rich environment and they will happily utilize that O2.