re-using yeast

[martin w]

for my last few beers i've been reusing yeast from a previous batch,normally by dumping it straight onto the yeast cake in the bottom of the fermenter.

i've been wondering if this is the best way of doing this,the fermentation normally starts pretty rapidly which is a good thing but is the yeast getting everything it needs to live a happy and contented life and get on with its job? 

after a couple of batches do i need to be adding any type of nutrient?

should i be removing and washing the slurry after each batch?or just storing the slurry in a sanitised container in the fridge?

how do commercial brewers do this?

i'm keen to hear others thoughts on this subject.

cheers

martin

[Llew Bardecki]

I've both re-used yeast cakes (many times) and washed yeast (a few times.) With a few exceptions, I usually just pitch straight onto a yeast cake these days.

My understanding of the situation is that by pitching on an old yeast cake you're usually way overpitching your yeast.

Many of the phenols and esters produced by yeasts are generated during the yeast multiplication phase, not during the main fermentation. And if you start out with enough yeast to ferment your beer WITHOUT it needing to multiply then you'll be missing out on these compounds. Thus for beers where these compounds are desireable (Belgians, Hefes, English ales) then you're probably losing something by pitching on to a whole cake. But for beers where you're looking for a nice clean flavour, this shouldn't be a major issue.

Further to this, if you're simply letting the same old yeast ferment one batch after another, you won't be getting many new, fresh, healthy yeast cells working on your beer. From what I've read this isn't a huge issue if you're only using your yeast for 2-3 generations, but it may become so if you're re-using it more often than that.

That's my 2 cents anyhow :)

(Edit: Actually now that I think about it, rather than pitching on a full cake, these days I more often add some boiled, cooled water to the fermenter, swirl it up and then split my yeast cake into 2 fermenters and do 2 batches with it.)

[martin w]

i have only been using the cake for 1 subsequent brew.
so after that 1 subsequent brew i should use mr malty's guide for how much slurry to pitch.how many times can i repeat this without doing anything? if the yeast is well oxygenated is it getting everything else it requires from the wort?

[JR]

If your worried about it you can get some Wyeast nutrients for a couple of dollars. Instructions on the pack say half a teaspoon for a 20 Litre batch ten minutes from the end. I use them in my yeast starters mainly but sometimes put them in the beer. I got mine from Dunedin Malt House.

[martin w]

i'm not so much worried as curious,i'm just trying to learn a little more on the subject. i know dumping on the cake ferments well, the airlock on my last beer was going ballistic after 3 hours and was pretty much done in 36.BUT, is it still doing the same as the original yeast was intended to do by keep re-using and if it isn't what can be done to remedy that? if anything?