Dark/Black layer of yeast on yeast cake- to use or chuck?

[Droopy Brew]

I have around 250ml of solid harvested yeast (1272) that is sitting under 400ml of fermented beer. It has been in the fridge for about a month and looks reasonably good- except it has a dark (closer to brown than black) layer of yeast on top. Now this wasnt there until recently so Im thinking it is dead yeast and I probably should have siphoned off some of the beer and replaced with DI water.



So I do not want to go down the vegemite smeared road of autolysis, is there anything I can do to use this yeast by somehow siphoning off the dark layer or spinning it up and decanting the healthy yeast off the top. Or is it simply not worth the risk and I should turf it?

 

[Alex.Tas]

This is what i would do droopy

1. give the jar a gentle swirl, till you get the layer of dark stuff off the top, up into suspension.
2. decant the liquid as best you can.
3. top up with water that has been boiled and cooled (so it is sterile) or i typically use bottled water. Do not use DI water. living things don't like living in DI water. it will suck the goodies out of the yeast!
4. shake it up and add to your beer.

Mr malty suggests that you only need 109 ml of thick yeast slurry for an average gravity brew, so you may only need half of what you have, if you plan to brew with this yeast shortly.



maybe post a pic of this dark stuff though. i get darker stuff settling on my yeast sometimes, but i wouldn't call it black.
here is a photo of some yeast i built up on my stir plate that i have for an upcoming experiment on two hefe yeasts at two separate fermentation temperatures (thread to follow closer to results). There is a dark layer that settled after some of the more flocculent yeast cells, but before the less flocculent ones.

 

[Matplat]

Hmmm, i had the same issue a few weeks ago I turfed the to be on the safe side... i have some yeast samples that were heaps older but still nice and creamy white so figured it was an infection in the black/brown layer. Alex am I right in saying that the layers in your samples formed immediately? Mine formed after a month or so... assuming it is infection I don't think there is any way you could knowingly extract perfectly sanitary yeast.

 

[Matplat]

I was pissed off too because it was 3068 that I had only used once! At least the batch it made was delicious

 

[Yob]

it's likely to have just been some older yeast, I have many with multiple tones and they fire up just fine.

You should always just run a starter if you are unsure, you'll soon pick up anything that's wrong.

 

[Jrrj]

Sounds like it would be worth using a yeast rinsing procedure. The protocol is described in Zainasheff and White's yeast book, but it is basically just sanitary re-suspension of the yeast in sterile water to separate it from dead stuff and trub. I am not an expert on doing this in practice yet, but it does look simple and no doubt many people on the forum can give you tips.

 

[Rocker1986]

I harvest yeast from starters and sometimes get a darker layer settling on top of the yeast in the jar. I always make another starter with these harvested jars, and have never noticed any problems with the resultant beers fermented with them. If it is autolyzed yeast, would the live cells in the starter use these dead ones as 'food' of some sort and kind of remove the problem? Have noted that when the flask is in the fridge crashing for a couple of days that this dark layer doesn't appear.

 

[Matplat]

Yeah i reckon there's a difference between a dark layer that forms immediately, and one that forms after a month or two.... but yob is absolutely right, a starter is the best method of determining if it is 'hazardous' or not. Wish I had thought of that before turfing!

 

[dr K]

Fresh, factory sealed, well maintained liquid yeast is relatively cheap and importantly easily obtainable.
Good techniques and using your harvested yeast fairly quickly will yield great results, making liquid yeast even more approachable.
A black scum/layer on the top says nothing but disaster....wild yeast and bacteria will make perfectly great starters, you may not smell or taste the difference until...too late.

K

 

[rude]

Cost a bit more to buy fresh packs but stuff it thats what Ive been doing
bloody hell busy enough trying to mash ferment without harvesting yeast

Always looking for the bargin 6 month old yeast but if it isnt there I go a new one

I use dry yeast a bit more for convenience these days thinking a good brewer should
be able to produce a reasonable job with it

I've pitched on a yeast cake once will prob do it again for a small then to a bigger beer

Good post though never heard of a black layer would worry me but sounds like some crew are
getting away with it

 

[Droopy Brew]

Thanks for the replies, I hadn't revisited this topic for a while. I ended up turfing it- too much invested in time and money to **** it with some dodge yeast. I still have that same strain going but, on about its 7th gen, I always get 2 harvests from a brew. Might make this current one the last one but, just to be safe. 7 brews from a $15 pack is good value.

 

[Yob]

IMO, its worth the experiment, 5L batch of DME and see what the hell happens, small starter and pitch, wait, watch.. I love little experiments like that..

Good rinsing practices should be enough to eliminate %95 of trub and anything else that isn't yeast (not bacteria n shit though naturally)..

If you are storing in the fridge, you want that yeast as clean as you can possibly get it, the yeast don't fully hibernate at those temps, just working extremely slowly... Only when in deep freeze do they essentially sleep and even then you want as clean a sample as possible.