Slow fermentation

[Dancing Camel]

Brewed an IPA 11 days ago that is still fermenting. Started out at 16.6 P, dropped to 10.5 within first few days but then slowed down to a 1/2 degree drop per day every day since. Ferment is still going, yeast are still in suspension and I don't pick up any off flavors or aromas. Any ideas or have my yeast just turned mischievous? Using second generation Fermentis US56.

[crassbrauer]

Do you regularly brew beers that big without this problem? Normally, beers of that gravity are hard on the yeast, since they're swimming in alcohol by the time they have fermented the wort down to 10.5 P. It's probably too late for this now, but next time you do another big beer like this, it would help the yeast along if you'd aerate the wort again 36 - 48 hrs after pitching. This allows them to increase their numbers even more in order to handle such a big job. Your pitching rate needs to be sufficient at the beginning, as well.

[grassrootsvt]

i use the fermentis 56 in several of our beers and have never had a problem such as that which you describe - whether with first or second or even further on in the generations. in fact, i have even pitched first generation, one .5kg packet, into a a 19 plato porter and a 23 plato triple ipa... second generation and onwards, i have used it for bigger beers without fail...even when underpitching, which on one occassion gave me a bit of sulfur, i had no problems completing the fermentation.
what is your fermentation temperature?
how well did you oxygenation your wort?

the only times that i've experienced this .5 plato drop per day is when using a first generation pitchable from white labs... or when fermenting a massive gravity beer at very low temperatures.

shaun e.

[Dancing Camel]

The temp isn't the problem - been sitting at 66 deg F since pitching. I don't think I'm underpitching since I pitched 5 gallons of slurry that I harvested just a week earlier. The oxygen might be a problem since temporarily, I'm still aerating with air. If I'm not sufficiently aerating though, wouldn't that give me a slower start rather than a slower ferment later on?

[crassbrauer]

You say you kept the yeast for a week. What did you do with the yeast after you harvested it? Did you aerate it and/or rinse it?

Aerating high gravity wort with the amount that you aerate a normal wort (11 - 12 P) would cause the behavior you've experienced. They would start normally then taper off.

[dick murton]

Sounds most likely like lack of aeration of the wort in both the first and subsequent brews. Different yeasts required different amounts of oxygen to work OK and stay viable. 16 plato is not a problem normally with single stage aeration / oxygenation - much above that may start to become a problem, but mainly due to production of undesirably high levels of esters. Yeasts require typically between 8 and up to 20 ppm oxygen in wort. You won't successfully get much above 8 / 9 / 10 ppm, depending upon the wort temperature using air. There have been plenty of discussions on aeration sinters / stones in the forums before. The air / oxygen needs to be oil free, odour free and sterile. If you haven't got an in-line wort aeration system, try bubbling suitable air of oxygen through the bottom of the FV for a while immediately after collection.

I don't recommend aeration after fermentation has started, as it tends to explode with the air causing much of the CO2 to come out of solution as almost an explosion - I've been there a few times, and it isn't fun. If you need to start aerating further, try to start after no more that 12 hours after collection. If you have to do this regularly, I suggest you change to oxygen instead of air.


You need to store your yeast cold - if you are keeping it at fermenting temperatures, half of it will have died by the time you pitch. Keep it at 2 -4 C. You may prefer to let it warm gently for a couple of hours before pitching but it doesn't normally cause a problem

[Dancing Camel]

The yeast was stored in our walk-in at about 4 deg C. I took it out in the morning on brewday to let it warm up to pitching temp.

Thanks to all - I get the message loud and clear. Time to get an oxygen tank.

Cheers.

David

[crassbrauer]

When brewing high gravity beers, German brewers routinely aerate 36 hours after pitching. These are lagers, which may not have produced a lot of CO2 by that time; plus they're going to produce more than enough, anyway. And yes, it is primarily to keep the esters down.

[dick murton]

Fair point. My experience of getting extremely well coated in yeast was with a 24P wort, fermenting at 20 C - all 500 hectolitres of it. It really knew how to get it's own back on you if you didn't treat it correctly, or left a manway door open.

Cheers