Just wanted to share the frustration. Kicked off an RIS this weekend. It started at 1.100, and its been fermenting furiously ever since. Trouble is, I’ve lost almost a gallon out the blowoff tube in krausen etc… Its a 5 gal batch in a 6 gal carboy. Apart from the obvious (get a bigger fermentation vessel) any suggestions to avoid this again? Fermcap? Does that affect head retention?
Fermcap as you mentioned. Fermentation temp. Try to keep the beer temp in the low 60’s to start & then as the fermentation starts to subside let it rise up a few degrees to finish. Make a 4 gallon batch to fit you 6 gallon carboy. Cheers!!!
Yes, Fermcap does affect head retention…it improves it!
And don’t forget, there’s also the school of thought that blowoff is a good thing - get’s rid of undesirables and such.
Thanks all for the input.
Hamilton - Its been fermenting in the low 60s as suggested, and now its a 4 gallon batch!
Denny - I’ll try the Fermcap next time
Hokerer - Agreed as far at hop undesirables, and I normally lose a little, but I’ve also lost a lot of potentially good sippin’ beer 
Yes, try the fermcap. I use it in most of my beers to prevent blowoff, as well as in the kettle to avoid boilovers.
I’ve tried the fermcap several times and whilst it has done a good job for me in the boil, in the fermenter it has never stopped a blow off.
Me, too. It is pretty amazing stuff and a 16 ounce bottle is pretty much a lifetime supply. I think it says to use 10 cc in 7 barrels or something like that. A couple of drops in boiling wort settles it right down and helps prevent boil-overs.
Use more. I start with one drop per gallon, and keep adding it every time I check if the krausen is building up again. I sometimes get up to 4 drops per gallon total, maybe 5. It works every time, and that’s with 5ish gallons in a 5 gallon carboy.
I don’t even measure. I just fill up the dropper tube and squirt it into the fermenter. Works every time.
When do you add it Denny, do you wait for krausen or do you add it after the yeast?
I wait to see if it’s actually gonna be needed, then add if necessary. The last few batches it was added once I saw that blowoff was starting. It killed the blowoff pretty much instantly.
I used a lot of the fermcap in one of my recent brews as much as 5 drops per gallon and the blow off refused to subside. This was using the West Yorkshire Ale (Wyeast 1469 I think) which after almost 2 weeks still has about an inch of krausen on top of it!
Ferment low, keep the wort temp in the low 60’s, especially for big beers, and I also use fermcap. I used to regularly launch lids, haven’t done that since I started cool ferments with fermcap, even with 15+% brews.
I regularly use this in the boil. My single attempt in the fermenter was a failure with a wicked blowout, but then again I just added it when I pitched the yeast.
As with the boil the drops need to be added to the fermenter when one sees foam! I suspected that. My only concern, and why it hasn’t been utilized further is possible contamination from the drops.
Any ideas/opinions on this? Are my fears unfounded?
All I can tell ya, Euge, is that I haven’t experienced any contamination from using them. Maybe I should add “yet!”. 
I saw that thread. Not sure what I’d do with a gallon if you’re using 5-6 drops at a time. That really is a lifetime supply…
I did it for financial reasons. The Williams anti-foam that I used quite allot went up to ten dollars per four ounces. I just couldn’t justify the cost. I paid sixty-three out the door for the gallon. Sure, it’ll last me for years but, I don’t have to think about it anymore. The company also sells Five-Star equivalent products, Lactic Acid and all kinds of everything else at wholesale pricing. For brewers that brew often and are in the hobby for the long haul, it just makes economic sense.