Pitching Unwashed Yeast Cake Slurry

Hey Y'all.

Rather than do the right thing and wash my yeast, I just swirled the trub/yeast around and put it in a sanitized 1Q cambro container. I now have 1 quart of yeast-looking stuff in my fridge. This is pretty much the whole cake from a batch of 1.062 OG Pale Ale w/ Wyeast Scottish Ale Yeast 1728.

I want to reuse this on an Imperial IPA, and am confused about how much to use and whether to make a starter or not. It will be 1.075-1.077OG. I am using this pitching rate calculator and can't figure out what the heck to plug into it:

Mr Malty Pitching Rate Calculator

The things I have no clue about are yeast viability, concentration, and non-yeast percentage. Any ideas? Is there a well established technique for reusing this slurry? Usually I make a 1L starter at 1.040 w/ a Wyeast smack pack and let it go for 18-24 hours before pitching. I shake it now and then.

Thanks!

How long ago did you put it in the fridge. Depending on that, I think you might just be able to warm it up, give it a shake to get everything suspended, let some of the non-yeast stuff settle out for 20 minutes or so and then decant it off into your wort.

If the yeast is fairly fresh (maybe a month old max?), the short answer is you could probably just let your yeast warm up to pitching temp and throw it in the imperial ipa. No starter. If its a whole yeast cake you will likely have enough yeast and there isn't really a concern with over pitching imperial ipa's.

The yeast was harvested yesterday and I'm going to pitch it on friday. Where does the "bad stuff" end up, settled on the bottom, or in the liquid at the top? Which part should I avoid?

How can I figure out how much viable yeast is in here? Is there a general rule?

Picobrew said:

The yeast was harvested yesterday and I'm going to pitch it on friday. Where does the "bad stuff" end up, settled on the bottom, or in the liquid at the top? Which part should I avoid?

How can I figure out how much viable yeast is in here? Is there a general rule?

Click to expand...

No, I don't think there is a general rule. You have trub, hops debris, cold break, hot break, etc, that can all be in there besides yeast. I don't know how you'd be able to calculate how much of it is yeast without a microscope.

YooperBrew said:

No, I don't think there is a general rule. You have trub, hops debris, cold break, hot break, etc, that can all be in there besides yeast. I don't know how you'd be able to calculate how much of it is yeast without a microscope.

Click to expand...

Well, it's "all the yeast" from the previous batch, so I thought maybe I could calculate how much it would have reproduced etc. Also, in my case, it is rather clean as there are no hops etc in the mix, just the break material and proteins. It is a homogenous tahini color.

A microscope sure does sound FUN tho... soon my garage will only be a brewery, and not a garage at all. It already can't fit any sort of car.

You'll be fine, I do it all the time. If you not sure, then just smell and taste the beer from the top of the jar before pitching. If the yeast is bad, then the beer from the top of the slurry will smell and taste bad too.
RDWHAHB

So is the RDWHAHB approach to just pitch the whole reserved cake slurry? That sounds easy enough... no starter then? I guess the risks/downsides to this technique are:

1. passing the trub from one batch to the next
2. potential overpitching

Is there any chance I'm underpitching or doing a disservice to the yeast by not gently awakening them in a starter?

No starter is necessary and you won't be over-pitching. Run it through a fine-mesh strainer first if you're really worried.

If you give your jar a good swirl and get every thing into suspension, and wait 20 min, most of the dead yeast and turb will settle to the bottom, and the healthy live yeast will stay in suspension.

Think of it like this, live yeast are a water balloon filled with water, dead yeast are popped balloons, so the dead ones are not buoyant and sink faster than the live ones.

If you mix them up, and let them settle before you pitch, and you pitch the milky top layer, you will get mostly live healthy yeast. and acording to Mr.Malty you should pitch ~150ml of that.

Bsquared beat me to it. Most of the dead/inert stuff will sink early. Most of the live stuff will stay suspended for a while.

150ml is nothing! I have a full quart... about 1000ml.... should I excercise restraint or pitch the whole batch?

Definitely use a blow off tube, fermentation will start quickly. My last pitch on a US-05 cake started bubbling in ten minutes!

When I'm reusing yeast I never wash it. I take note of how much break material is in the fermenter before I pitch the yeast in the batch I'm going to be reusing yeast. Most of the time I don't even need that, I get about the same amount each time. I dump everything into a 1 gallon growler. Then use the pitching calculator to make a best guess at yeast concentration and non yeast percentage.

Picobrew said:

150ml is nothing! I have a full quart... about 1000ml.... should I excercise restraint or pitch the whole batch?

Click to expand...

Well you don't really want to over pitch, unless you plan on lagering. Over pitching can lead to problems, and excessive cell death which can ruin head retention, and add off flavors. I know it does not seem like a lot but its close to 3 vials of WL yeast.

I save my yeast slurry for a couple weeks in the fridge and use it for a few batches before dumping it. I got a 100ml glass pipette that I can sterilize with a flame for pulling out the yeast I pitch and minimize contamination risks. Pouring multiple times for the same container can be risky.

I'm still voting for pitching it all. If you were doing a Hefe or a Belgian then I would consider using restraint with the pitch rate but not with an Imperial IPA.

I pitched the whole thing last night. Was bubbling like a jackhammer this morning with a 2 inch krausen. Churning away, looking good.

When you're done, you can wash the cake and split it up into several jars. Common wisdom is that the yeast is best on it's third generation. You oughta be able to get 2-4 batches from IPA from that cake now. And it'll be conditioned to higher gravities.