Are all yeast slurrys created equal?

[BenB]

When it comes to using a pitching calculator (such as Mr Maltys), can you use the "yeast slurry" to confirm you've got the right amount of yeast after completing a multi-step starter. IE the calculator says I need 400 billion cells for an upcoming brew. The stepping up calculator (from Brewers Friend I think) says with the 50% viability I should have in my 2007 smackpack (from date of production) a 2L followed by a 1.6L should do the job.

But..... the pack spent a while in the post, no idea how its transported from the states etc and in the 24 hours since I smacked the pack and despite a fair bit of shaking the smack pack has only inflated 50% and when I opened it to pitch it didn't have the usual CO2 acidic / yeasty niff. It's clearly got some viability still but I really doubt 50%!

On that basis I'm assuming my 2.0L/1.6L step-up is likely to be inadequate. After I cold crash the 1.6L I'll be able to approximate how many mL of yeast I've got in the bottom of the 2L flask. Would that work? I've always assumed the "yeast slurry" was referring to yeast in the bottom of a FV and would somehow be different to yeast in the bottom of a starter (less trub / coagulated hop resins / dead cells etc etc).

Or (unless I get a microscope and check) do we assume yeast slurry = yeast slurry = yeast slurry.

The Mr Malty site suggests 2 billion / ml for a "loose slurry" and 10% non yeast. That seem the right ball park?

[rpt]

I wouldn't worry too much about it. Pitching rates are only a rule-of-thumb anyway so you probably have plenty of yeast. This assumes you are brewing an ale - for lager you possibly have to be a bit more careful due to the low fermentation temperature and lighter flavour.

[BenB]

Yup. It's a lager

Although it appears that yet again I won't be brewing due to yeast issues. I pitched the semi-swollen starter into 2L of starter wort Thursday morning and 48 hours later nothing- no bubbling, no foam, no CO2 smell. Getting a big annoyed with the smackpacks when they're sent in the post. It looks like if you use them as soon as they arrive they're fine (already at room temperature!!!) but if you stick them back in the fridge it nukes them. I've double checked the fridge temp where I store them and its 4 degrees.... Just over 2 months old smackpack- no action. The fact it swelled a little makes me wonder if there's a few yeasties still in there but I'm worried their viability is terrible. So thats 4 smack acks (£30) DOA in a just two months...

I think from now on I'm going to either just order the yeast to order (hoping they have the one I need in stock) or do the two-hour round trip so I can keep it cold in the coldbag in transit.

Grrrrr....

[rpt]

Have you tried White Labs? They don't come in smack packs and I've certainly had no trouble storing them in the fridge before using them.

[BenB]

Yes, I am considering switching! Of course now the starter has started showing some activity. Admittedly not much and some 50 hours after pitching but we have definite bubbles. Whether it's contamination or the 2007 finally getting it's arse in gear I have no idea. I suspect a 2L starter is mahusive for what appears to be a low viability smackpack so I suspect the yeast growth won't be massive- have pulled the Yeast book off the shelf to have a read to try and decide what to do next! Perhaps in retrospect I should have pitched the poorly perfoming smack pack into a 1L starter and taken it from there....

[Dennis King]

I moved from Wyeast to Whitelabs because I found the smack packs a pain in the arse. Brewlabs slants are also a good option.

[Matt in Birdham]

Take a look at this article by Kai. The suggestion is that the MrMalty calculator isn't that accurate for stir plates, and one of the conclusions is that stir-plate starters (or perhaps any starters?) are less sensitive to the original amount of viable yeast than the MrMalty calculator predicts. If you accept Kai's conclusions, then it does make estimating yeast counts quite a lot easier, given that you don't need to have a super accurate initial pitching count. This yeast calculator on Brewers Friends is, I think, a lot better than the MrMalty one and gives you the option of various growth-rate algorithms, including Kai's one which I now use.

Having said that, I still went down the path of trying to get my pitching rates more "in the ballpark" at least (as opposed to pissing in the wind, which was pretty much my old approach).What I have ended up doing is overbuilding (a la Brusolopher) and then storing the extra in 50ml centrifuge tubes. Once the yeast in these compacts down, you have (apparently) a fairly reliable count of 5-8Bn cells per ml, and a pretty good handle on how much you will be pitching into your next starter. I have roughly "confirmed" these calculations, in that I have created starters especially for storage and e.g. made 4x tubes with 50Bn cells compacted yeast which correlated nicely with the 200Bn I was trying to make in the starter. At least now I feel I am within an order of magnitude of what I am aiming for, whereas before (especially with slurry) it was really finger in the air stuff.

Here are a couple of the tubes just after filling from a starter. After a week the yeast compacted down to 7.5ml, around 50Bn cells (according to the Yeast book). The tubes are pretty handy things, about 50p each off ebay and they arrive sterile:

[McMullan]

If you are that way inclined, get a microscope to take a look. The reality is slurry is worse than you might think, in terms of viable yeast count. The best strategy is a nice viable colony or two stepped up. Much more predictable than slurry, in my experience. 'MrMalty' is a load of bollocks, beyond massive errors in pitching rates. If wort is optimised for yeast growth, adding 'too little' means more growth; adding 'too much' means less growth. An FV full of optimised wort has a carrying capacity for the yeast population. Superstitious home brewers beg to differ for some unknown reason... I guess it's down to the blogoshere or something

[BenB]

Yes, I'm tempted. My mother in law's a microbiologist so I spent a few hours at the weekend discussing cell counts! I was amazed to discover they do all their cell counts manually (obviously usually bacteria rather than fungus). I suspect though that most of the time the cell counts are fairly ball park- if someone has an infection the exact cell density isn't that important!!!

I'm working on the more is more approach for pitching rate. I've got the 2L starter crash cooling in the fridge, going to decant it tomorrow (actually I'm going to syphon off the supernant- try and avoid disturbing the slightly fluffy yeast cake). Then I'm going to pitch it onto the next starter. Hopefully that will give me a nice load of fairly on-the-ball yeast to pitch.

The cold crashed yeast has a slightly unusual appearance. Rather than being trub with a layer of yeast on top from the bottom upwards it goes pale cream then trub (grey) then a nice settled cream layer again. I wonder if the bottom layer is the dead yeast from the smackpack... Hmmmm.