Proper yeast nutrition means your brew ferments faster and cleaner, leaving fewer off-flavors that have to age out. We’ll call that a good thing. Yeast is a pretty complex little organism, though, with a lot of nutrient requirements that change from life phase to life phase. So how do we, as mere homebrewers without lab support (most of us, anyway), best support yeast in our various brews?
Last weekend I posted Ken Schramm’s excellent article from Zymurgy on feeding yeast, including lab tests. I’ll be the first to admit this article can be a tad daunting, though it’s well worth wading through. There are some background resources you may prefer to start with. Both White Labs and Wyeast have excellent information online about how yeast works and its various phases: lag, log and stationary, with or without respecting a rest phase in there. (Here is a good overview of the yeast life cycle by White Labs, and here’s a doorway to the Homebrew Enthusiasts pages at Wyeast. Both are pretty much beer-oriented, though many of the same principles apply.) If you’re not aware of the Homebrewtalk forums, you’ll find a wealth of information there – including a thread about fermentation and yeast.
I’ve seen the estimable Ken Schramm suggest a couple of ways to nourish your yeast. A simple way is to add 1 g diammonium phosphate (DAP) and 1/2 g Fermaid K (Lallemand micronutrient blend) or equivalent at pitch and 24 hour intervals for 3 days. That works very well. Remember the goal is to prolong the growth phase as much as possible without overfeeding the yeast, to provide a source of micronutrients and to supplement potassium levels, which are particularly lacking in lighter-color honeys, which tend to have lower mineral levels. A biggie: mead must is low in free amino nitrogen, one of the first things your yeast will need. The goal is 200 ppm for an alcohol level >20%. Honeys mostly don’t have that much.
From the article linked above, here’s the extract version. For a traditional 5-gallon batch of mead with a starting gravity above 1.120. Remember that it is more effective to calculate your additives in weight than volume.
1. Rehydrate at 104F w/Go-Ferm or other organic rehydration nutrient at rate of 1.25 g per g of yeast.
2. Add 3 g Fermaid K or equivalent plus 4 g DAP per 5 gallons w/vigorous aeration at end of lag phase (6-12 hours, at start of obvious fermentation activity). For gravities above 1.125, increase by additional 25%
3. 1 g DAP plus 1 G Fermaid K or equivalent w/vigorous aeration at 12-hour intervals until 50% sugar depletion or 5 days, whichever is first.
4. Potassium bitartrate or potassium phosphate at 300 ppm.mineral levels. I will be the first to tell you I haven’t figured out how to calculate 300 ppm mineral levels. Your must needs potassium, and these are two good food-grade varieties you could use.
Melomels have special considerations, as anyone who’s had the vigorous fermentation blow their airlock knows. Most fruit provides an excellent source of yeast nutrition. Here’s what Ken suggests for dealing with a melomel 5-gallon batch:
2.5 gallons water
8 lbs honey
rehydrate yeast with Go-Ferm or equivalent and water at 104 degrees F
When must have moved through lag, add 3 g Fermaid K (1.5 tsp) or equivalent
When must is in log fermentation add fruit and pressed juice and rest of honey
Stagger addition of DAP at 1 g .24 tsp every 12 hours plus .5 g (.125 tsp) Fermaid K until 50% sugar depletion