Reusing Lager Yeast

[squirt in the turns]

I brewed a Czech style pilsner on Sunday, 95% Weyermann pils, 2.5% melanoiden, 2.5% Caraaroma, bittered with Hallertau Mittelfruh and Saaz and finished with Saaz only. Chilled to about 14C using the plate chiller, then put it in the fridge overnight to get it down to 7C for pitching (yeast was at the same temp). O.G. 1.050.

Yeast is WY2001 (Urquell Pilsner), from a month old smack pack, propagated in a 2L starter on a stir plate, then added to 5L without constant agitation (7L total starter volume). I chilled and decanted beer off before adding to aerated wort.

Hopefully I get a good, clean, complete fermentation and am left with a nice big cake in the primary for reuse for the next lager, which will be another pilsner, possibly a double-decocted SMaSH. After that, I’ll try to use the cake again for something bigger and darker like a dopplebock.

Obviously lagers and especially light pilsners are very vulnerable to any unhappy flavours that might result from flaws in my process. But, if done right, this is surely the best way to build up sufficient cell counts for really good lager ferments?

My questions are:
Will my next pilsner be ok if pitched directly onto the cake of the first one, assuming everything turns out great by that stage?
When, if at all, should I wash the yeast? Assuming sanitation is good and my primary schedules are more or less back-to-back, is there more risk in adding this step in, or just reusing the yeast as-is?
Are lager yeasts different to ale yeasts in this regard? Could I maybe get 4 batches out of one pack, with a slightly higher gravity beer like a helles bock between the 2nd pils and the dopplebock?

Cheers!

[drsmurto]

Yes, you can repitch another pils on top of the yeastcake.

No need to wash the yeast although if repitching a few times in a row it's a good idea.

Due to the much colder fermentation temperatures it is harder to overpitch a lager than an ale. I personally wouldn't pitch an ale onto an entire yeastcake unless you are going from standard OG to something big like a barleywine or RIS. A cup full of yeast is more than enough, assuming the previous ferment was happy, healthy and tastes fine.

I try to get 3 beers out of a lager yeastcake, the first from a starter, the next from an entire repitch and the 3rd from half the yeastcake of the 2nd beer. That is three standard OG beers. I could go more but 3 lagers is my limit for a run as they take up so much more time fermenting and lagering. I'm on my 3rd in a run at the moment that started just before new years. Smoked marzen (10L batch) - vienna lager - bo pils. The smoky flavour hasn't come through in the vienna lager and i didn't wash the yeastcake. Might brew another lager once the bo pils is done, probably something smoky as the first batch was only 10L and I am loving it.

[squirt in the turns]

Thanks DrS. I see that you've started with a medium coloured beer, gone slightly darker, then gone very light (making some assumptions about the marzen and vienna there). I take it that the flavour/colour of the bo pils isn't noticably affected by the previous beers? When you do an entire repitch, is it in the same fermenter? If not (or when harvesting for a partial pitch), do you make any effort to separate the yeast from the rest of the trub?

If I transferred fresh wort onto the whole cake each time (my 3rd and final beer being a dopplebock with an O.G. of, say, 1.085), could I get away with reusing the same fermenter, with no cleaning (all other factors being as santiary as possible)? 3 beers over approximately 9 weeks in one vessel?

[drsmurto]

Rauchbier is the darkest of the 3, vienna is lighter but still quite amber and the bo pils the lightest but it did get a double decoction so not as light as you might think even though it is 100% pils malt.

I collect the yeastcake after racking the beer off and let it settle in the fridge overnight or longer. Pour off the beer and pitch only the slurry. That way less off the colour/flavour of the previous beer comes through. I don't separate the yeast from the trub unless i plan on storing the yeast for any length of time and then use the method described in the link in my signature.

I personally don't reuse fermenters, preferring to start off each time in a sanitised container. The krausen skum ring is also something i don't want in my beer as this contains quite nasty tasting compounds. The effort involved in swirling the yeast with the last litre of beer to loosen it and pitching it into a new wort in a freshly sanitised container is minimal.

[squirt in the turns]

The 1st pils is still in primary, having been there for 4 weeks today. I dropped the temp by 1or 2 degrees per day last week, getting to 0 on Friday. Had intended to rack, harvest the yeast and brew the next pils over the long weekend, but life got in the way and I now probably won't brew the next batch until later this week or possibly longer.

I'm now thinking I should rack ASAP (hopefully today), wash the yeast as per drsmurto's instructions, and get it going again with a starter 1 day prior to brewday. I believe it's best to pitch an active starter for yeast harvested in this way to avoid putting it through too many growth/dormant cycles?

Is that the correct process?
Between washing and pitching into a starter, I intend to store in the cold conditioning fridge at 0 C, in a flask with boiled and cooled water. Is this method OK? Assuming temp is OK so long as it doesn't freeze?
How big should the starter be? Will it need longer than 1 day at ferment temps (~9 C)? Going into a 20 L batch of approx 1.050 wort.

Cheers!

[drsmurto]

There is no need to rack per se but it is what i would do to remove the beer from the dead yeast cells, flocculated proteinacous material etc that is in the cake at the bottom of your fermenter.

If you plan on brewing in the next week or 2 then i would be comfortable repitching the cake without making a starter or washing it. Any longer and i would go through the washing/starter process linked in my signature.

Starters should be done at growth temperatures which are 21+C. I tend to aim for a minimum of 24C. The starter process is about making yeast, not beer and you tip off the wort pitching only the yeast slurry. 9C will result in much slower growth. 24 hours at 24C is fine for a starter followed by overnight at 1C to floc out the yeast.

When storing yeast cold is best so 1C is what my cold conditioning/yeast storage fridge is set to.