Questions about multiplying liquid yeast

[Fore]

I'm planning my next round of brews, one of which (AG#4) will be a Duvel clone. I never thought I'd be looking at liquid yeast so early, but it seems like a good play with such a high gravity brew.

In planning a 20 or 23l brew, the WYEAST pack says "1B cells, good for 20 litre", but one recipe I saw said 2-3 packs (or a starter) needed. Another recipe actually specified 3.5B cells necessary. The recipes seem to tie up, suggesting the WYEAST marketing is a little optimistic.

Can you confirm that one pack won't be sufficient for a 20l Duvel clone?

If so, I'm already wondering about a starter. If I understand right, I need to start a 1.040 ~26 degrees "mini-brew", aka starter, about 2 days prior to the main brew, then decant off the wort and pour the yeast slurry into my main brew. If so, what sort of volume am I looking at for the starter of a WYEAST pack? Am I right in thinking this will about double the cells, to 2B? Will even that be enough?

 

[MyQul]

The easiest way is to just use a yeast calculator

MrMalty is a very popular one

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

ButI prefer this one because is has an overbuild and starter facility to it

http://www.brewunited.com/yeast_calculator.php

As to pitching the starter itself you can either pitch the whole thing as long as it's not more than 5% of the brew length or decant off the spent starter wort and pitch mostly just the yeast

 

[clibit]

Can you confirm that one pack won't be sufficient for a 20l Duvel clone?

One won't be enough, for sure. One option would be to make a one litre starter with a single pack and make a 10 litre batch, then use the yeast produced by that to make another, larger batch. Or, do the two step thing, make a ten litre batch and then add another 13 litres of wort after about 3 days. I reckon you could do a ten litre batch without a starter, as long as the pack is not close to its use by date. But a one litre starter would guarantee a healthy batch of yeast.

Otherwise, Mr Malty suggests you need a 3 litre starter made with two packs, to make a 23 litre batch.

 

[Fore]

Thanks both. I've just learnt a lot from those calculators. I like Brew United. Wow, you can see immediately why someone might want to get a stir plate.

Makes me think I'm stepping too far too quickly though.

Might stick with 2 dry packets for now, to test the ground so to speak. Best to tie down my basic recipe & measurements before I start to complicate the process further. Still, good to know about the different approaches possible. In the meantime I can think over which process would suit me best, and look at picking up a proper starter kit (or at least a glass container of sufficient size). 1 pack of S-33 & 1 pack of T-58 (idea found on the web); sound OK?

How sterile do you need to be with a starter? For dry yeast rehydration I use boiled cooled water, and a starsan'd container. I guess that suffices for a starter? Is tin foil over the top OK, or airlock recommended?