MrMalty question...

[Darren Andrews (Daza)]

Hey on the MrMalty website the tabs at the top I don't understand it is the viability % value and the date to select to. dooes it go on grain bill size and abv size? I want to do a 6 gallon or 23L batch and the grain is 7.5kg the abv is 7.3% from what I put in using viability of 70% (thought it was meaning efficiency) and cam up with 1.8 pkts of dry yeast...now does that sound right? should it be 2 packets of US05 for that size brew? cheers guys.

http://www.mrmalty.com/calc/calc.html

Daza.

[oliver]

So the viability % is all about the cell count of the yeast. You can roughly figure out what the approximate cell count of the yeast is based on it's shelf life. For US-05 the shelf life is 2 years, so find the best before date on the packet and punch that (- 2 years) into the 'production date' field. The viability % will get updated for you from the date.
Common wisdom is that a lot of people underpitch and it's quite difficult to overpitch so I always round up, even if the calculator says 1.1 packs, just go with 2 packs, don't short-change yourself on yeast as you'll run a higher risk of getting off flavours in the finished product.

[Darren Andrews (Daza)]

Thanks Oliver, so best before date, and then minus 2 years from that? like 12/10/16 would be 12/10/14 entered in to the date box? and yeah I have heard that under-pitching is a common mistake made, on the packet they say good for 20 to 30 litre batch but that must be bull? and I have read on here somewhere that with a high abv best go with 2 packets like over 7%....(I think that's what  I read) I am having a krausen too that doesn't want to drop off yet, when googled it is pretty common with the US-05 dry yeast but they all say on that forum that it will drop just be patient. Some still hang in there 3 weeks mine has been 8 days today. So not that bad bubbles just stopping now. Checking gravity again tomorrow. cheers.

[oliver]

Yep you got it. Not necessarily bull, especially if the yeast is fresh. The other factor people look at (apart from viability) is vitality. Vitality is how healthy the yeast is. So if you have really healthy fresh yeast you might be able to get away with pitching less I guess. Personally I like to hedge my bets so I like to overpitch slightly with the freshest possible yeast.