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Hochkurz double decoction AND a really long boil for an impy stout?

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nateo:

--- Quote from: morticaixavier on March 13, 2012, 01:43:36 PM ---I have always wondered about the whole incremental feeding thing, not understanding how it helps to feed incrementally when the net effect is the same level of alcohol. But if it's an issue of osmotic presure that makes sense to me. as the gravity goes down you can add more sugar without exceeding the presure threshold! thanks nateo!

--- End quote ---

Whether or not osmotic pressure matters really depends on the health of the cell walls, but even healthy cells have trouble over 1.120. I've read (don't remember where) that osmotic pressure inhibits fermentation even down at like 1.060 if the yeast have poor cell membranes. The pressure will literally squeeze nutrients out of the yeast, like squeezing a wet sponge, only instead of water, nitrogen comes out, inhibiting their fermentation performance.

hopfenundmalz:
Was using my phone earlier.  Thanks for getting the link to Fred's page up, Nateo.

Here is what is on White Labs' page.
http://www.whitelabs.com/beer/homebrew_super.html

nateo:
I would be incredibly careful adding nutrients, if you do. Wort has a really high level of yeast available nitrogen (relative to any other growth medium). Too much nutrient will cause off-flavors, and if you add too much at the wrong time and the yeast can't use it all, it could potentially feed bacteria.

Adding O2 multiple times keeps the yeast in growth mode. They make like 33x more alcohol per cell during the growth phase than during the stationary phase. This is related to incremental feeding of nitrogen, but again, be careful not to overdo it.

nateo:
The more I think about it, the less adding nitrogen to beer fermentation makes sense to me. I haven't found many hard numbers for yeast available nitrogen content in wort, but one study found a typical range to be 1-2g/L, or 1000mg/L - 2000mg/L.

Brewers' yeasts' nitrogen requirements aren't published, but wine yeasts' are. The "standard" winemaking yeast available nitrogen recommendation at 28 Brix (1.120) would be 375-425mg/L. Wine yeast nitrogen requirements vary pretty widely, with some needing nearly twice as much as others. I assume beer yeasts are similar in that regard. Even if the yeast needed twice the nitrogen, that'd only be 850mg/L, well below the minimum reported amount of yeast available nitrogen in wort.

In order to need nitrogen for a wort fermentation, you'd need to have a very nitrogen-deficient wort, and a yeast with exceptionally high nitrogen needs.

EDIT: Thanks MX, fixed it. Nitrogen =/= nutrients.

morticaixavier:

--- Quote from: nateo on March 14, 2012, 08:21:39 AM ---The more I think about it, the less adding nutrients to beer fermentation makes sense to me. I haven't found many hard numbers for yeast available nitrogen content in wort, but one study found a typical range to be 1-2g/L, or 1000mg/L - 2000mg/L.

Brewers' yeasts' nitrogen requirements aren't published, but wine yeasts' are. The "standard" winemaking yeast available nitrogen recommendation at 28 Brix (1.120) would be 375-425mg/L. Wine yeast nitrogen requirements vary pretty widely, with some needing nearly twice as much as others. I assume beer yeasts are similar in that regard. Even if the yeast needed twice the nutrients, that'd only be 850mg/L, well below the minimum reported amount of yeast available nitrogen in wort.

In order to need nutrients for a wort fermentation, you'd need to have a very nutrient-deficient wort, and a yeast with exceptionally high nutrient needs.

--- End quote ---

this is an interesting idea. However you are only looking at 1 nutrient. Perhaps it would be worthwhile to find a yeast nutrient with low or no N but I have noticed (in a very unscientific way) better results when using nutrients then when not, at least with big beers.

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