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redbean
02-12-2010, 11:20 PM
I have a question about oxygenating mead. I have a background in making wine. I can remember occasions when I earned the winemakers severe disapproval when I screwed up and accidentaly added oxygen to their wine. As I write this I am realizing that their oxygen phobia was more pronounced post-fermentation (I imagine post-fermentation oxyphobia is a common trait of meadmakers as well?). However, the winemakers seemed intent to avoid it at every step. I am struck with the absolute disparity. Everybody making mead seems to swear by adding as much oxygen as possible during fermentation. I've looked into it a little and I suspect that yeasts can produce either aerobically or anaerobically and that this depends on the sugar. My guess is that the sugars in honey differ from the sugars in grapes. Am I on the right track? If I am can anybody break it down for me?

Oskaar
02-13-2010, 12:28 AM
From one of my earlier posts (edited for readability).

This is from Dr Clayton Cone of Lallemand who is the reigning yeast guru in the wine industry.




From Dr. Clayton Cone of Lallemand:
Yeast need a trace amount of oxygen in an anaerobic fermentation such as meadmaking, winemaking and brewing to produce lipids in the cell wall. With out O2 the cell cannot metabolize the squalene to the next step which is a lipid. The lipids make the cell wall elastic and fluid. This allows the mother cell to produce babies, buds, in the early part of the fermentation and keeps the cell wall fluid as the alcohol level increases. With out lipids the cell wall becomes leathery and prevents bud from being formed at the beginning of the fermentation and slows down the sugar from transporting into the cell and prevents the alcohol from transporting out of the cell near the end of the fermentation. The alcohol level builds up inside the cell and becomes toxic then deadly. Lallemand packs the maximum amount of lipids into the cell wall that is possible during the aerobic production of the yeast at the factory. When you inoculate this yeast into your must, the yeast can double about three time before it runs out of lipids and the growth will stop. There is about 5% lipids in the dry yeast.

In a very general view:
At each doubling it will split the lipids with out making more lipids (no O2). The first split leaves 2.5% for each daughter cell. The second split leaves 1.25% for each daughter cell. The next split leaves 0.63%. This is the low level that stops yeast multiplication. Unless you add O2 the reproduction will stop. When you produce 3-5% alcohol beverage this is no problem. It is when you produce higher alcohol beverage or inoculate at a lower rate, that you need to add O2 to produce more yeast and for alcohol tolerance near the end of fermentation. You definitely need added O2 when you reuse the yeast for the next inoculum.

Dr. Clayton Cone

Basically as budding occurs, the new generation of yeast needs oxygen. Oxygen in trace amounts will not slow or stop the anaerobic cycle, but will in fact help the yeast to ferment more rapidly and aggressively. Also of note is that during the aerobic and the early anaerobic phase of fermentation the yeast will produce up to and above 30 times the amount of ethanol that will be produced in the rest of the fermentation. This in the presence of oxygen, especially during the first 72 hours of fermentation. Hence, oxygen will not slow, stall, impede or otherwise muck up the works for a good strong anaerobic ferment after most of the alcohol has been produced in the early stages.

Note that Dr Cone is specifically dealing with wine, but the oxygen needs of most yeast are consistent from media to media (i.e. honey must to grape must) I have a background in winemaking as well, but, unlike your experience I see that most winemakers here in California are very much on board with micro-oxygenation and aeration during the fermentation.

Also, please avail yourself of the search tool here on the forums as most questions you may wonder about have been address in part or even fully at some point.



Hope that helps,

Oskaar