Top Cropping Yeast (in pictures)

Share your experiences of using brewing yeast.
Wolfy

Top Cropping Yeast (in pictures)

Post by Wolfy » Fri Sep 21, 2012 12:38 pm

Top cropping is a useful way to harvest clean, fresh and healthy yeast, it's done while the yeast is actively fermenting and it's best pitched immediately into a new batch of beer.

When working with yeast, it's best to be as sanitary/sterile as possible. Chemical sanitizers (like Starsan) are useful, but using heat to sanitize should be better again.
The only equipment needed to top crop yeast is a suitable spoon and container for the yeast. An all-stainless ($2 Asian soup-serving) spoon and pyrex jug work well, and can be heat-sanitized (in boiling water for 15mins).
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While the actual top cropping procedure is deceptively simple, it does require a few things to 'go right' before it can be attempted.

Firstly you need to be working with a yeast that allows top cropping; during the active fermentation phase, the yeast will float on-top of the wort with a sizable, active, 'rocky' type head. The yeast (most often top-fermenting Ale strains), wort, temperature and other factors will determine if top cropping is possible (sometimes it may even be possible to top-crop a bottom-fermenting lager strain).
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The trick to successful top cropping is getting the timing right, you want to top crop the yeast when it's most active, when there is a large amount of healthy fresh yeast floating on-top of the wort, usually this time is called 'high krausen'. In some situations this might be over a 2 or 3 day period, in other cases it might be a matter only just hours, attempting to top crop to early or too late will not work if there is not sufficient yeast to harvest.
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As can be seen in both the photos above, two days after pitching, the yeast (Wyeast London Ale III, Wy1318) is forming a raft 70-100mm in height above the wort with a nice rocky/solid/yeasty head, making it the ideal time to harvest the yeast by top cropping. However, the exact time when yeast can be top-cropped depends on many individual factors and there is no generic rule that can be followed, the fermenting beer must be checked periodically and top cropped when the yeast is ready.

Top cropping is only possible when using a fermenting vessel that allows access to the surface-yeast, top cropping with enclosed fermentors is not usually possible.

Using the sanitized spoon, first skim-off (and discard) any trub/break/protein or hop debris that sometimes floats on top of the yeast:
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Then scoop up the fresh, clean yeast:
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Continue the process to harvest enough yeast as required:
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Since we have harvested only clean, fresh and 'pure' yeast, somewhere about 50-150ml should be adequate for pitching into a standard sized batch of fresh wort:
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Depending on the conditions and time the yeast is harvested, it's possible that the yeast can be top-cropped again later (sometimes it will take only hours for the yeast to be ready for additional harvesting):
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(Photo taken a short time after the top cropping shown above)

Top cropped yeast, harvested at high krausen is fresh, healthy and active, so it's best to pitched immediately into a new batch of fresh similar composition wort, where it will likely 'kick off' very quickly. If you are not able to use freshly top cropped yeast, it might be better to wait and harvest the yeast after fermentation has completed and the yeast has settled.

Edit:
Wyeast have some information on their website that suggests yeast should be harvested after the gravity has dropped below 50% of original gravity and that the first 'dirty crop' (taken after 24-36h) should be discarded. While ensuring the gravity has dropped might help prevent harvesting too much yeast too early, monitoring the gravity that closely (or often) might be difficult for home brewers, I also wonder if discarding the 'dirty crop' is essentially the same as simply skimming the gunk off the surface before cropping clean yeast.

Edit 2:
After posting the pictures above (and being surprised how little gunk there was floating on the top of the yeast) I recalled that about 16 hours after pitching the yeast (when there was already a krasuen starting to form) I shook the fermentor around to re-aerate it a bit more. This might also be the equivalent of Wyeast's suggestion of discarding the 'dirty skim'.
Last edited by Wolfy on Sat Sep 22, 2012 3:39 am, edited 3 times in total.

weiht

Re: Top Cropping Yeast (in pictures)

Post by weiht » Fri Sep 21, 2012 12:49 pm

A silly qns really, but would the beer face attenuation problems if I skimmed most of the yeast from the surface?

Wolfy

Re: Top Cropping Yeast (in pictures)

Post by Wolfy » Fri Sep 21, 2012 1:01 pm

weiht wrote:A silly qns really, but would the beer face attenuation problems if I skimmed most of the yeast from the surface?
As per the pictures, harvesting the ~150ml of yeast (more than adequate for a new batch of beer) took only a few spoons, and there was still a fair amount of yeast left floating on-top.
There is also much yeast in suspension fermenting the wort, but depending on the time (in fermentation cycle) and how much yeast you harvested, I guess it's possible - in theory - to harvest too much and have problems later.

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far9410
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Re: Top Cropping Yeast (in pictures)

Post by far9410 » Fri Sep 21, 2012 1:32 pm

Great post and pics ! :)
no palate, no patience.


Drinking - of course

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Kev888
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Re: Top Cropping Yeast (in pictures)

Post by Kev888 » Fri Sep 21, 2012 3:16 pm

Another very useful post!

Cheers
Kev
Kev

50quidsoundboy

Re: Top Cropping Yeast (in pictures)

Post by 50quidsoundboy » Fri Sep 21, 2012 3:33 pm

any tips for storing top cropped yeast (for maybe a week or so)?

Wolfy

Re: Top Cropping Yeast (in pictures)

Post by Wolfy » Fri Sep 21, 2012 5:00 pm

50quidsoundboy wrote:any tips for storing top cropped yeast (for maybe a week or so)?
It's my understanding that as yeast finish the fermentation process they prepare for dormancy by building up (carbohydrate) 'food' reserves (glycogen and trehalose).
These reserves might help extend the shelf-life of the stored yeast (which is less of an issue if it's stored for a 'week or so'.
But most importantly, when pitched into a new batch of wort those carbohydrates help the yeast adapt, acclimatize and start a healthy fermentation.
Hence if you top-crop you are taking the yeast while it's most active (and essentially in a feeding-frenzy), then if it's stored immediately (essentially starving it) it may not be 'as prepared' for storage or 'as prepared' for future fermentation since it may not have adequate reserves of those carbohydrates.

I presume using a stater before pitching the yeast (not having to do so is another advantage of top-cropping and pitching immediately) would get the yeast ready for your new ferment.
However, if it was me, I'd likely leave the yeast in the fermentor, then harvest and rinse the yeast in 'a week or so' when the beer is bottled/kegged.
But there is an element of selective-breeding when top cropping, so if that was important to you, you might want to top crop it then store it anyway, it might also be easier than harvesting then rinsing the yeast-cake, so I'd just keep it in a sterile (as possible) container (glass jar) in the fridge until you are ready to use.

50quidsoundboy

Re: Top Cropping Yeast (in pictures)

Post by 50quidsoundboy » Fri Sep 21, 2012 5:02 pm

thanks - sounds like a good excuse to do a second brew on tuesday after my brew day this sunday....

Wolfy

Re: Top Cropping Yeast (in pictures)

Post by Wolfy » Fri Sep 21, 2012 5:10 pm

50quidsoundboy wrote:thanks - sounds like a good excuse to do a second brew on tuesday after my brew day this sunday....
And you needed an excuse to brew more beer? :)
2-3 days should be fine top cropping, but yeast can at times be fickle and unpredictable, so if you have to brew to a human-schedule and not what the yeast dictate, it's useful to have a pack or two of dry-yeast in the fridge just incase what you want to do does not match what the yeast actually do. :oops:

greenxpaddy

Re: Top Cropping Yeast (in pictures)

Post by greenxpaddy » Sun Sep 23, 2012 7:11 pm

Another great how to post Wolfy

I am top cropping for the first time. The gravity is down by a third but the kresuen is still more like washing up foam than creamy yeast. Do you think I am still too early? Its a cool fermentation of ale yeast 17 degrees at 48 hrs after pitching.

Don't want to miss my chance though...

Wolfy

Re: Top Cropping Yeast (in pictures)

Post by Wolfy » Mon Sep 24, 2012 6:23 am

greenxpaddy wrote:I am top cropping for the first time. The gravity is down by a third but the kresuen is still more like washing up foam than creamy yeast. Do you think I am still too early? Its a cool fermentation of ale yeast 17 degrees at 48 hrs after pitching.

Don't want to miss my chance though...
That's the part that makes top-cropping more an 'art' than a 'science' there is no answer I can give that is 'right' because it all depends on your yeast, wort-conditions, temperature and other factors - much of it can only be 'learned' by looking/seeing/doing a few times. Even then each beer/yeast tends to be different, often the 'best' answer is to go with what you feel is right at the time, and what you expect the yeast/fermenting beer will do - you might never get a thick yeasty-head with this batch, it might only be thin-foam ... who knows. ;)

greenxpaddy

Re: Top Cropping Yeast (in pictures)

Post by greenxpaddy » Mon Sep 24, 2012 7:44 am

Cheers. I did a trial run yesterday and the foam just disintegrated into a watery solution. There is some yeast there but it's not going to be enough. I checked fermentation this morning and it's more lively, so the halfway gravity rule might be bang on. In theory I guess we are looking for the yeast to start clumping together which will only happen once the easier fermentable sugars have started to be depleted.

I'll try again tonight.

Wolfy

Re: Top Cropping Yeast (in pictures)

Post by Wolfy » Mon Sep 24, 2012 8:00 am

greenxpaddy wrote:I checked fermentation this morning and it's more lively, so the halfway gravity rule might be bang on.
I think that's another thing that depends on yeast/wort/conditions (but presume Wyeast have it as a good/generic suggestion).

He's my Brewlab F40 (TOP clone), 12 hours after pitching:
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I had to make a blow-off-cap for it:
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Now 6 hours later (18 since pitching), there appears to be more than enough yeast to pitch into a new batch (its a 2L glass bottle).
... essentially automatically 'top cropped':
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greenxpaddy

Re: Top Cropping Yeast (in pictures)

Post by greenxpaddy » Mon Sep 24, 2012 11:53 am

Will you discard that dark brown top layer in the bottle?

Wolfy

Re: Top Cropping Yeast (in pictures)

Post by Wolfy » Mon Sep 24, 2012 11:58 am

greenxpaddy wrote:Will you discard that dark brown top layer in the bottle?
In theory ... yes. ;)

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