Quote:
Originally Posted by giligson
Yes, yeast needs nitrogen sources: DAP is the standard nutrient. Different manufacturers have various strategies to sell you their product. Some include Vitamin B, some include yeast autolysis products or trace minerals etc - most of it is marketing.
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Not really. If you surf over to the Lallemand website, you'll see there are lots of links to technical studies of fermentation kinetics, and they have spent a significant amount of $$ studying just how, when and why yeast look for particular nutrients at certain times during the fermentation process. If you're naturally suspicious of a manufacturer's own studies and data (and by rights you should be), then you can find similar study results published by UC Davis' Enology labs.
For one thing, DAP is an inorganic nitrogen source, which yeast cannot assimilate once the ethanol concentration in a must gets up above about 8% ABV. For additional nitrogen supplementation past that point (say, to reduce a yeast's production of H2S), you need to use amino nitrogen from an organic source (such as autolyzed yeast). Likewise, in order to maximize the ethanol tolerance of your yeast and minimize the production of off-flavor creating byproducts during fermentation, various vitamins and minerals are needed throughout the yeast's lifespan.
Beer brewers needn't worry so much about the finer points of yeast nutrition -- basically all the micronutrients that yeast need are usually found in grain-based wort, so a little nitrogen supplementation is usually all that is necessary, and DAP is perfectly fine for that. Even grape wine producers typically don't have to be as concerned -- grapes provide similar micronutrients, and a goodly amount of amino nitrogen, so often only some additional supplementation with DAP is needed -- although some yeast strains benefit from additional amino nitrogen and additional micronutrients.
But meadmakers -- we're the poster children for managing problematic fermentations, since honey supplies only the sugars needed for fermentation, and scant if any additional yeast nutrients.
Bottom line is that you can get a fermentation, of a fashion, from a honey must with no additions. You'll get a much more complete fermentation with a little DAP added early on. You'll get an even faster, more complete and more "clean" fermentation from a careful regimen of nutrient additions if you understand what you're doing when you make those additions.
The choice is yours.
Mead Nutrients Confusion
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