[Finn Berger]

Query:  if the zinc is in the trub, would carrying over some trub from the boil kettle carry over sufficient zinc to the fermenter (from a late boil addition of yeast nutrient) to aid in the yeast health?  Also if harvesting yeast post ferment (and immediately re-pitching same), would the trub in the fermenter be worth harvesting with the yeast for its zinc content? 

I guess I will be adding the zinc in sterile water or wort solution into the fermenter going forward….

I've seen a study on the first question there, but I don't remember it now. I think the answer is that the yeast can use at least some of it. However, unless you do carry the trub with you as part of your routine, I wouldn't start doing it because of the zinc.

I have bought some zinc sulfate heptahydrate. (A little will probably last you a lifetime:).) A solution of that will not be where unfriendly life forms would chose to settle down. I keep it in the fridge, and I just add what I need of that directly to the wort along with the yeast, using a pipette. I make the solution like this: Mix 10g ZnSO4•7H2O with 990g of water. 1ml per 10l of wort will add 0,227 ppm - give or take a few thousands:) - of zinc to the wort. That's what I use for ales. For lagers, I'll use only half as much, as lager yeast needs less than ale yeast.

This seems to work well for me. I've based the dosage on Palmer, who says that "zinc levels should be between 0,1 - 0,3 mg/L, with 0,5 mg/L being the maximum" (HtBr, p. 99). I've seen smaller numbers, though - the 0,05-0,15 range is common. So i'm not very certain about what is ideal.

Caveat: That dosing is based on the assumption that the yeast has no sizeable stores of zinc. If you've given it zinc in a starter, or if you're using new yeast (dry or liquid), you shouldn't add any - or maybe just very little. You should keep track of your additons, because the yeast has the ability to store zinc. Accumulation over fermentation cycles will be detrimental.

Ideally you should monitor the zinc content in your wort. I guess breweries do that, but I don't know of reasonably priced test kits for home brewers. I'm not going to lose much sleep over this, though:).

Oh, by the way: If you're making a solution, it should be quite acidic. If not, you will get a greenish precipitate.