New yeast eating old yeast in starter?

I recently made a starter of 002 with a vial that was 8 months past its "best before" date. I wasn't expecting much, but after 48 hrs on the stir plate, it started showing signs of life. After another 48 hours, I took it off and tossed it in the fridge.

The next day, when everything settled, there were two layers. One was a small dark ring on top, and the other was a lighter band on the bottom. I poured off the liquid,made a 2 liter starter, and threw it on the stir plate for 24 hours. After 24 hours, it was alll clumped up, so I put it in the fridge.

After 24 hours in the fridge, after everything settled, there was only one layer and it was all a light brown, thick layer of yeast. I then tossed it into a batch of mild, and let it do its thing.

So my question is, what happened to the second layer after stepping it up, and why was the layer of yeast much lighter after the second step? I was thinking maybe the new, strong cells ate the old, weak cells. I'm not worried about anything, just trying to understand it a little better. Anybody ever experience this?

Its possible the first starter wasn't finished and some undissolved sugars fell out after the yeast did. Purely a wild guess, i get some layers too, then stir it up another day and everything is a nice milky yeast color

I think that you got something like this https://www.homebrewtalk.com/f163/yeast-layers-look-inverted-331367/, right?

If it is the case, everything is normal. The dark band is just old yeast cells settling on culture.

New cells are heavily clumped and precipitate early than old cells, forming a white creamish band on jar/erlenmeyer. On the other hand, old cells are less prone to precipitate and take more time to settle. When you made a starter, you promote the cell growth on culture and this explain why the dark band disappeared.

Remember that yeast cells can not eat each other...they can only absorb single nutrients from culture/wort.

Yeah, kinda. It looked like the second picture, except the band of darker stuff was much thinner. I was thinking about it backwards, figuring the dead yeast and trub would have settled first. Thanks for the information and the link.

diegobonatto said:

Remember that yeast cells can not eat each other...they can only absorb single nutrients from culture/wort.

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It sounds like your saying yeast cannot eat each other but take other cells nutrients, is that what you mean by "culture"?

I think somewhere in my travels a lab nerd has said something similar, but taking it one step further by saying they will eat each other. For example, if on a stirplate too long.

Sure that yeasts cannot "eat" like protozoans (endocytosis) or animals, but yes, they can absorb nutrients released by other yeast dead cells or autolysed cells.

But yeast are Cannibals. They actually lyse cells that are adjacent to themselves. As they lie dormant and their interior nutrients deplete, they are actually able to destroy the cell membranes of their neighbors, causing the neighbors' nutrients to leak so that the perpetrator can absorb those nutrients.

Yeasts are able to induces cell's lysis only if they have the "killer" character, specially during the active growth phase. I'm not sure if it is the case of all brewing yeasts strains.