[MileHighBrewer]

Recently I have been getting relatively low attenuation during my fermentations.  I've run into the problem with White Labs London, British, and California yeasts.  I aerate well, start out at the right temperature and ferment at the right temperature, but still get poor results.  I am concerned that it might have something to do with the size of the carboy and the blow off tube I am using.  For the primary fermentation, I typically put my cooled wort into a 5g carboy, but when the fermentation really starts going off I lose a lot of Krausen out of the tube.  Since ale yeast is top fermenting, could I be losing a lot of yeast out of my blow off tube that could negatively affect my fermentation?  Should I use a 6g carboy instead for the primary?

Any thoughts are appreciated!  Thanks.

[morticaixavier]

you should use at least a 6 gallon container for primary on a 5 gallon batch. some folks use anti-foam in the fermenter and report good results. I just use a bigger fermenter.

other details would help as well, are you all grain or extract?

if extract have you switched extract manufacturers? different maltsters produce extract of different fermentabilities.

If you are all grain, have you calibrated your thermometer recently? A too high mash temp could result in poor attenuation.

all that aside though, if you are blowing out most of your good yeast that could cause a stall or at least a really slow fermentation.

try a batch in your 6 gallon carboy and see if it works any better.

[MileHighBrewer]

I am brewing all grain.  I am pretty sure my thermometer is accurate, but will test it.  I'll also start using a 6g fermenter for the primary. Thanks - I appreciate the advice!

[duboman]

I am brewing all grain.  I am pretty sure my thermometer is accurate, but will test it.  I'll also start using a 6g fermenter for the primary. Thanks - I appreciate the advice!

Definitely calibrate your thermometer. +1 on Mort's comments, it does sound though like you're mashing at a higher temperature than you think.

[HoosierBrew]

+1 to the bigger fermenter.  I use 8 gallon plastic wine fermenter buckets.  I used carboys for years and ended up getting a couple severe cuts. Went to these big buckets and never looked back. They're cheap and I can put 5.5 gallons into the bucket with plenty of headspace to spare.  Even the crazy WY3068 and 3787 can ferment like hell and stay contained.

http://shop.greatfermentations.com/product/7-9-gallon-fermenting-bucket/plastic-fermenters

[klickitat jim]

Dang! If they were clear I'd be all over it.