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These food grade silicone stoppers feature several vent holes lightly sealed with a silicone top flap. Gases can escape, but cannot get in. Just put the stopper on your carboy, and forget it. No worries about evaporation or water getting into your fermenter. This #7 size is pictured at left above, and fits virtually all glass carboys. Made in USA.<P>
Click here for a pdf of cleaning and dissasembly instructions.
I was concerned about the "slippery" reviews, but found this to be no more of an issue with silicone rubber, than with any other kind of rubber. Yes, rubber is slippery when wet, but I find the same techniques work with traditional rubber or these silicone stoppers. I find that a quick alcohol rinse dries quickly and leaves the rubber super sticky. It dries quickly and is less slippery than sanitizer solution. An additional dab around the neck of the fermenter makes for a super tight/sticky fit. I like these best for secondary fermenting since you don't have to monitor liquid levels in a bubbler. 3-piece bubblers are still great for primary fermentation, as I like the handy reference/index of being able to track "bubbles-per-minute". For long-term & secondary though, these stoppers are TOPS!!
Using this with a plastic fermenter lid is ideal. This stopper works great in a 1.25" hole drilled in the lid as it fits snugly. It 'burps' off surplus CO2 and seals it self after fermentation to prevent oxygen ingress or 'suck back'. It has handled modest blow off from vigorous ferments without clogging, although I doubt it's foolproof in that regard. I prefer to clean it and resterilize it after such an incident and, thankfully, even cleaning after a messy blow off incident is relatively easy. As long as you have something to clean the holes with, it will look as good as new.
Another advantage is that it seems to withstand the ultimate homebrewing sterilization technique: an autoclave cycle (using a pressure cooker). It does seem to discolor a bit after this type of heating, however.
Slickness with glass as reported by other users seems quite plausible, but I used to have that issue when using the standard rubber stoppers with glass as well.
I had been very excited to use this but when I placed this in my secondary after racking it started slipping out almost immediately. I watched it over the next couple of hours to see if it would stop and still hold a seal but it eventually came almost all the way out before I decided it to switch it out with a standard stopper and airlock. It isn't a pressure buildup problem, but the stopper is just too angled and slick and the angle forces it right back out of the glass fermenter.
I ended up trying it again. This time before placing it in the carboy I rubbed the outside of the stopper and inside of the carboy neck with rubbing alcohol and let it dry completely. It stayed in after that, so I may use it when cold crashing, but it is a pain to do this for normal fermenting.
Just sanitize and pop it in. No need to maintain water levels or worry about breaking your last flimsy plastic airlock.
I have had them pop out on me once or twice right after interting it. But it's been several batches of beer since that's happened. Maybe there is still mold releaser on the silicone that takes tome to go away.
We tried to use this with a glass carboy. If there's any moisture in the neck, this stopper slips right out. I don't want to stick anything into my carboy neck to dry it out, or leave it open to dry on its own. So I did not find this stopper useful.