Cell count and top-cropping

[carpedaym]

I'm brewing my first beer and had planned everything to a "T" including using the mrmalty calculator to get my yeast cell count right.

If I've pitched the right amount of yeast, do I need to be concerned about top-cropping the yeast and reducing the overall amount? Or by high krausen is there more than enough yeast?

Yeast is dry US-05. I'm doing a 13L batch so I pitched 6.5g of rehydrated yeast. Smaller brews = more experimenting with style.

 

[slash22000]

Top cropping is not intended to reduce yeast cell count in the beer. It's to use the cropped yeast to inoculate a second batch of wort.

 

[carpedaym]

Yes, I plan to top-crop the yeast so I can reuse it in a week or two for another batch. I am wondering whether if I top-crop this fermentation, will it be left short of yeast cells in the current fermentation? Or is the cell-count really only a concern when it is first pitched and is undergoing the reproduction phase?

I've read under-pitching can cause unwanted flavours, and I'd rather taste a textbook US-05 fermentation so that I can wrap my head around it and figure out what suits my tastes.

Edit: clarity

 

[verysupple]

I'm not professing to be a yeast expert but lots of people have had success (including me) by simply collecting some yeast slurry after fermentation is complete. This seems a lot easier than top cropping and eliminates your dilemma about reducing your cell count - I don't think it's really an issue but if you want to be safe...

EDIT: These links might be useful:

http://byo.com/stories/article/indices/58-yeast/2634-re-pitching-yeast-boil-timing

http://byo.com/stories/article/indices/58-yeast/2577-second-generation-techniques

 

[carpedaym]

Great articles, verysupple, thanks. The benefits of harvesting after fermentation seem two-fold:

1. don't have to worry about messing with the current brew either by reducing yeast or by introducing infection,
2. yeast won't be sitting around as long until the next brew.

I had considered rinsing the yeast after bottling but the top-cropping sounded easier. Perhaps the bottom-cropping, which is outlined in your second link, is the way to go.

Still curious though, about the cell count's importance after high krausen.

 

[Amber Fluid]

I didn't think US05 was very good for top cropping???

If I were you I'd either:
1/ take some of the yeast cake and just pitch that into the next one you want or;
2/ take some of the yeast cake, rinse it then pitch into the next one you want.

 

[manticle]

I think you are worrying uneccessarily.

Can't give you anything more solid than that but the yeast gathered from top cropping is super active and super healthy and I've never experienced flavours I could relate to underpitching when doing it.

Top cropped yeast is healthier than slurry although I personally wouldn't bother with 05 just because it's easy to use and cheap.

 

[hsb]

Wyeast website has some best practice advice:
http://www.wyeastlab.com/com-yeast-harvest.cfm

Open Vessels (Top Cropping): Yeast can be harvested once the gravity has dropped below 50% of original gravity. First head will rise approximately 24-36 hours into fermentation. Discard 1st skim (“dirt skim”). A clean, 2nd head will rise which can be harvested with a 2nd skim.

Talking out of my hat but isn't there an element of helping the current brew along when top cropping? Encouraging further yeast growth or something? Flamesuit on, hat back on.

 

[Wolfy]

If you want to use the MrMalty calculator to estimate how much top-cropped yeast to pitch into your next batch, use the "Repitching from Slurry" tab and set the 'Yeast concentration' to as high as it will go (thick slurry) and the 'Non yeast percentage' to 0 (since you should have harvested only fresh yeast when top cropping).

 

[Lecterfan]

@Wolfy and Manticle, as I read it, O/P is worried amount the number of yeast cells left behind in the brew he is top-cropping from, not whether or not he has healthy amount going into the next brew.

A good question. I have no evidence or support, but personally I would not top crop from a yeast that is not specified as a top cropper for this very reason. Wy1007 and wy1469 seem to replenish their yeast numbers at high krausen quickly having no detriment on the beer left behind. I would not be certain that this is the case in a yeast that is not commonly known for its top cropping potential.

Others may have a link to a more definitive answer or something.

 

[carpedaym]

Lecterfan, your interpretation is correct.

Thank you all. It sounds like certain yeast strains are recommended for top-cropping exactly because they won't be left short of yeast troops for the current fermentation.

I didn't realise US-05 wasn't a top-cropper. That's probably going to determine the path forward on this particular brew. I know it is a cheap yeast, but I figure I might as well practice on a cheapy so I'm more confident when I start getting the liquids. Looks like I'll be practicing my rinsing instead, unless this pitch looks like it has a lot of krausen on it.

 

[manticle]

@Wolfy and Manticle, as I read it, O/P is worried amount the number of yeast cells left behind in the brew he is top-cropping from, not whether or not he has healthy amount going into the next brew.

A good question. I have no evidence or support, but personally I would not top crop from a yeast that is not specified as a top cropper for this very reason. Wy1007 and wy1469 seem to replenish their yeast numbers at high krausen quickly having no detriment on the beer left behind. I would not be certain that this is the case in a yeast that is not commonly known for its top cropping potential.

Others may have a link to a more definitive answer or something.

I got that. I think it's a non-issue.

 

[felten]

Thank you all. It sounds like certain yeast strains are recommended for top-cropping exactly because they won't be left short of yeast troops for the current fermentation.

The top cropping tag is to do with how much yeast actually migrates to the surface, some strains of yeast will have a large amount on the surface you can harvest, and some just won't.

If you pitch enough healthy yeast initially, you don't have to worry about top cropping wrecking your beer (unless you introduce an infection or something).