Harvested Yeast - What are these layers and do I have too much?

Question

I harvested yeast a few weeks back from my hefeweizen (Wyeast 3068) which I had open fermented. To harvest, I scrapped it right off the top, after ~36 hours of fermenting, with a sanitized spoon. I then plopped it in my sanitized mason jar. I am now looking to use this yeast again, and noticed a few things when I pulled the mason jar from the fridge, which leads to my questions.

1. There appears to be two VERY SLIGHTLY distinct layers of yeast sediment on the bottom of the jar. Is one of these good, and the other bad?
2. To me, this looks like a ton of yeast. Based upon the answer to the previous question...would you pitch all the 'good' yeast in this jar, or try to only pitch a portion of it? And would you make a starter?

Answer 1

The bottom layer contains more trub, but does also contain yeast. The top layer is formed after the majority of the trub has already settled, so it's more or less pure yeast on top.

You don't have too much - actually the opposite. It's best to make a starter - even though it looks like a lot of yeast, it will be vastly underpitched in a 5 gallon brew.

I'd guess from the scale on the jar that's about 80ml of yeast sediment. Washed yeast is about 1 billion cells per 2ml, but after more than 2 weeks, viability is below 50% so, 1 bn cells per 4ml is the maximum yield here. So, in the ~80ml you've got an estimated 20bn cells.

Since this isn't lab grade yeast culture, you'll want to pitch around twice what wyeast recommend, or about 1.5 million/cells per ml per degree plato, or 220 billion cells into a 5 gallon batch for a 1.060 beer. As you can see, the 20bn cells you have is far short of that. That's why I would use a starter.

Pitch all of it into a 1 or 2 liter starter (size depending upon how much yeast growth you want in the fermentor) and you'll get much closer to recommended pitching rates.

Answer 2

Look at this page http://www.wyeastlab.com/hb_pitchrates.cfm by wyeast to estimate the amount of yeast you have.

If it were me I would split that into 4 smaller containers, and do a starter from one of them for my next batch, while trying to be close to the amounts determined by the wyeast link.

Answer 3

When in doubt, start it out. All you'll end up with is healthier yeast. Although there are arguments that trub is beneficial to yeast, I'd take the healthy section and grow it up.

That being said; many times I've just re-used yeast without separating and no starter with splendid results. However, some caveats: 1) I always made certain there was sufficient cell count (had enough volume to do the trick) and 2) I've only brewed under tightly controlled circumstances - too much love and labor to chance open fermentation in my world.

Keep it clean and good luck.

Answer 4

First, I have noticed this sort of layering in carboys during fermentation.

I wouldn't pitch it all. I would just use part. A starter may help but I have never used them. Your basic tradeoff is that the yeast will be more active when you add it. The downside is it is another opportunity for contamination. My philosophy is keep it simple. Maybe some others brew better beers and meads than I do, but it works for me.