Top cropping

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Permalink Reply by Dougal on June 4, 2012 at 10:54pm

Yup, it's pretty much that easy. The hardest part is timing when to collect. I read somewhere the norm is when the beer is 2/3 of the way to final gravity. I just wing it and try and collect a couple of days before it starts dropping. 

Depending on the strain, it can help to have the collection jar half filled with cold, sterile water, as the yeast/foam settles better in the cold water and you can pack more in. You won't need to rinse it. 

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Permalink Reply by Liam Callaghan on June 5, 2012 at 10:24am

Interesting to see how you get on Paul, seems you might be able to make your yeast go further with that method of yeast collection.

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Permalink Reply by Dougal on June 5, 2012 at 10:45am

The best thing is that top cropped yeast is extremely healthy and pure. It's usually clean white with none of the usual trub and detritus you'd expect from bottom collected. I don't know how long you could store it as it probably hasn't built up glycogen reserves, but I've had some great beers from pitching top-cropped yeast soon after collection.

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Permalink Reply by Liam Callaghan on June 5, 2012 at 12:20pm

Does it have less chance of mutation so you can get more generations out of it?  That's what I think I gleened from Yeast, but I'd need to go back and check.

Without the glycol reserve how long do you think you should store it before use if its stored in cold wort?

Also why do you discard the first layer?

My beer stocks are almost out so I will be brewing after work over the next few weeks, might be ideal for that.  I can pitch immediately then.  Especially if I brew every 2-3 days.

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Permalink Reply by Dougal on June 5, 2012 at 1:53pm

Not sure about the mutation question- it is less stressed I suppose as it hasn't had to endure the higher alcohol level of completed fermentation, so it might be less mutated?

You store it in cold sterile water, not wort, in order to completely stop activity. I've used it after two weeks and had good results, but I'd still shoot for one week for best results.

The first stuff that comes to the top is that darker waste material that ends up in the krausen ring, so you skim that off and crop substantial-looking yeasty foam that comes next.

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Permalink Reply by Paul Fraser on June 5, 2012 at 6:31pm

Thanks. It's good to know it's that easy.

So would you say that after a couple of days or so, to skim the first layer off then wait a day and collect the good stuff? And you're really saying that if you're brewing within 2 weeks then it's ok to use top cropped yeast but if it's going to be longer then it would be best to rinse the yeast once racked to bottling bucket as they will have to glycol reserves to survive longer?

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Permalink Reply by Dougal on June 5, 2012 at 8:26pm

Sounds good to me, though timing is a bit different for every yeast. 

The two week thing is my own presumption though, so don't assume it's scientific. If you use a pitching rate calculator I don't know the viability drop would be too far different between top cropped and bottom collected, but after a brush with an infection I've become a bit of a nazi about not using old yeast :-)

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Permalink Reply by Richard Jack on November 30, 2012 at 12:35pm

Does anyone know a rule of thumb regarding the quantity of the middle skim to repitch into an identical batch? The whole lot? A portion? Or treat it like slurry and calculate it via mr malty?

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Permalink Reply by jt on November 30, 2012 at 12:44pm

I hadn't thought of that. I'd probably use mrmalty and set the concentration higher and the non yeast percentage lower

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