What would cause yeast to fail to flocculate?

Question

I am using WLP002 - English Ale Yeast - in my current batch, a Young's double chocolate clone. According to the manufacturer's product page, this yeast is highly flocculant.

The beer remained in the primary for 15 days. After this time, the gravity had fallen from an OG of 1.070 to 1.021. This is a 70% apparent attenuation, which is the top end of the expected range for this yeast. There was a lot of yeast still floating on top of the beer, but I racked to the secondary anyway. Here is a picture of the secondary after three days. That is yeast on top. Last night, after two weeks in the secondary I used a small spoon to pull a bunch of this out and verified by smell that it is definitely yeast. I also took another gravity reading and found that it fell from 1.021 to 1.018 in the secondary. I now have an apparent attenuation of 74.2%, kind of high for this yeast. Yet, the yeast remains atop the beer.

Why is the yeast not flocculating? Might it be that the high amuont of lactose (12 oz.) and/or cocoa powder (6 oz.) in the beer is making the beer more dense than the yeast? I'd like to see this yeast fall to the bottom before I bottle, else it will end up slurrying the beer.

Answer 1

Yeast will fail to flocculate for a variety of reasons. In your case I think the biggest factor is the yeast are still active. As long as yeast are still actively eating sugars and haven't fallen into survival mode, they'll stay in solution where the food is. Once they die they should flocculate.( here is the yeast life cycle in beer ) I would wait for the gravity to stabilize before worrying or trying anything else with this batch.

Another common reason, is temperature. If the beer is kept at too warm of a temperature, the yeast will flocculate less than when it is cold. If the gravity is stabilized and the yeast still aren't flocculating I'd put it somewhere cold and more of the yeast should flocculate.

If the gravity is stabilized and it's in a cold place, and the yeast still aren't flocculating, I would look into fining agents, such as gelatin, or isinglass. Fining agents act as coagulants for the yeast (and other things) in the beer.

I doubt the amount of lactose or cocoa has much affect on the yeast flocculation. I made a very chocolaty stout a while back with 3 pounds of chocolate and my final gravity was much higher than yours. I had no issues with yeast flocculation.

There is one other thing that I just noticed. part of your OG (assuming you added chocolate/lactose in the boil) will be non-fermentables. This would throw off your calculations of % attenuation. I would definitely leave it somewhere warm until it ferments out, as I suspect the yeast isn't done with it's meal yet.

Answer 2

I would suspect also that the little bit of fat from the cocoa powder may be coating some of the yeast and making them more bouyant. Also creating aggregates that trap gas like White labs said.

Anothe cause of poor flocculation is low calcium levels in your brewing water. Yeast need calcium as part of the flocculation process. You can't do anything about it now, but maybe next time add in some extra calcium chloride or calcium carbonate. But by next time you won't be rebrewing the chocolate stout, so its a meaningless comparison at that point.

It is weird, because WLP002 is a viscious flocculator normally. I bet its the fat content.

Answer 3

I'm answering my own question on behalf of White Labs. I contacted them about this and here's what I got back:

A lot of times with these flocculent strains, air pockets (or CO2 pockets) will cause the yeast to rise to the top. It is strange for this strain not to flocculate very quickly, but it is possible for something like this to happen. Once the beer gets chilled, it should settle out with no problems. I have a feeling there is just a lot of gas trapped in the cell clusters, causing it to float.

I'm going to check the gravity again tomorrow. If it's still at 1.018, then I'm going to cold-crash the carboy in a fridge for four or five days and see what happens then.

Answer 4

Saccharomyces cerevisiae has a barm flocculation pattern, which means ale yeast floats to the top when it flocculates. This is because the more open structure of the yeast is caught by the rising carbon dioxide. After fermentation is complete and your specific gravity has stopped decreasing, drop the temperature of your beer below 46˚F (7.8˚C), the yeast will drop within 24 hours.

Answer 5

Thank you for your comment, I kind of suck at answering questions and I am trying to get better at it. Sorry if I am ever to vague. I’ll improve I promise. Anyway, the whole thing with ale yeast verse lager yeast flocculation patterns lies in the shape the flocs make when suspended in beer. Ale flocs are almost like a parachute that gets caught by the rising carbon dioxide bubbles, which lifts the yeast up to the top. When you drop the temperature of the beer the yeast are no longer happy and they go into an almost hibernation like state. So they are no longer making ethanol or carbon dioxide out of your sugary wort. With the absence of CO2 bubbles the yeast sinks to the bottom because nothing is keeping them up. If you dropped the temperature of your beer before fermentation finished, (so maltotriose and maltose sugars are still in the wort) than when you warm the beer back up the yeast will wake up and happily continue eating the sugar and making carbon dioxide and alcohol. If there is enough sugar there to produce an abundant amount of carbon dioxide your yeast will float to the top, if there isn’t they may just float up a little bit or even stay on the bottom of your vessel.

If all of the sugar was assimilated by the yeast before you dropped the temperature and you warm the beer back up, the yeast would do a few different things, one of which is start to convert by-products of the fermentation process like the vicinal diketone diacetyl into a flavourless compound called 2,3 butanediol. The yeast would start to float in the beer again, but it probably wouldn’t rise as rapidly to the top, instead the beer would look a little cloudy. As far as the other fermentations are concerned maybe not enough yeast was pitched to create a rapid fermentation so there wasn’t an abundant amount of CO2 to raise all of the yeast up to the top of the vessel as happened with this one. Maybe you just over pitched this last fermentation and this is why you were seeing more yeast than usual. An increase amount of oxygen in your beer would create sterols and the ability for your yeast to continue budding new daughter cells. If you over oxygenate your wort, a lot of yeast would be made. This would create a lot of CO2 and yeast which may be what you saw floating around at the top. If you pitched more precisely or did not over oxygenate previous batches of beer this same effect would be less noticeable. Did I help at all?