No, Not gravity dependent, re hydrating etc… as that relates straight to pitch count that your doing a close number just cell count wise using tools such as mr malty or doing the long math yourself. Yes rehydrating has some pros/cons but in most cases your pitch count is still well over the mark so a few killed, not rehydrated cells don’t matter much in the grand scheme of simplifying homebrewing for the masses.
Grainbelt, I thought you had already seen-participated in all of these conversations over the last year really bringing this topic of no O2 for dry yeast to life.
Denny’s correct as pitch counts so high, growth is one of the very least concerns and then we move onto the main reasons outside of growth into why starters, O2 etc… is essential with liquid as these yeast are low in sterol count also if not treated correctly will ferment with sick symptoms as outlined briefly below.
In Dry yeast not alone is it the high pitch count the sterol reserve is way higher than you would ever have in a slurry/liquid pitch of any sort. I have said this time and again but dry yeast is prepacked with up to 5% sterol reserves and a properly prepared slurry of any type will hold maybe >1% sterol content before starting the anaerobic fermentation phase. All this means to the layman is at the end of brewing cycles or before making a starter liquid yeast are sterol difficent. IE:<1.0% they then need O2 to build sterols during the aerobic phase which then leaves them replete with >1% sterols in which to see proper cell growth and healthy anaerobic fermentation. Yeast can and will ferment a beer with low <1% sterols but you will have higher incident of dead/ non viable cells and petite mutants and budding is a haphazard operation so fusel production and other ester production can be exaggerated also which is all byproducts of sickly yeast.
Here is a good FAQ that has been covered before in a conversation between Shadetree and myself he found coming directly from one of the dry producers website.
http://www.danstaryeast.com/frequently-asked-questionsI always aerate my wort when using liquid yeast. Do I need to aerate the wort before pitching dry yeast?
No, there is no need to aerate the wort but it does not harm the yeast either. During its aerobic production, dry yeast accumulates sufficient amounts of unsaturated fatty acids and sterols to produce enough biomass in the first stage of fermentation. The only reason to aerate the wort when using wet yeast is to provide the yeast with oxygen so that it can produce sterols and unsaturated fatty acids which are important parts of the cell membrane and therefore essential for biomass production.
If the slurry from dry yeast fermentation is re-pitched from one batch of beer to another, the wort has to be aerated as with any liquid yeast.
