Cold crash what? It's the Cold Crash Guardian!
If you ferment in a temp controlled environment and enjoy the benefits of cold crashing, the inevitable problem is that the cooling in the fermenter creates a vacuum. The worst case scenario is that the liquid from your airlock or blowoff container gets sucked back into the beer and some portion of air from within the refrigerator is also drawn in. This has both contamination and oxidation effects on the beer even if you haven't noticed it yet. If you've jumped on the New England IPA craze, even tiny amounts of oxygen will destroy that beer.
There are very few discussions being had on this topic and when it is brought up, those concerned are often told not to worry about it or offered solutions that don't work. Scroll to the bottom to read about some of these misguided solutions.
What you get:
This simple but effective kit includes a 1 gallon expandable bladder connected to a tee. The tee is pressed into a hole in a drilled stopper, grommet or carboy cap (you provide) and the top of the tee connects to an included hose that is dangled into a container of starsan solution (you provide). We include 4 feet of tubing which can be cut as necessary. We also include hose barb splice and elbow fittings that you can insert into the stopper in order to get the tee further away from your fermenter if necessary.
How it works:
As your wort ferments, the CO2 inflates the bag full, then excess pressure is vented through the blowoff tube and bubbles through the starsan in your catch container. If yeast and trub is blown through the assembly, it will collect in the starsan container as with any other blowoff setup. If any debris makes it into the bladder, which is unlikely, it can easy be cleaned out by removing the cap from the bladder.
Once fermentation is over and you set your fermentation temp controller to COLD, the vacuum created in the fermenter will start to draw the CO2 out of the inflated bag as necessary. In most cases, the bag will deflate about a 3rd of the way for 5 gallon batches and half way for 10 gallon batches. No starsan will draw up the tubing. More importantly, only CO2 will be drawn back into the headspace. No oxygen, no starsan, no bacteria.
The barbs on the tee that insert into your fermenter are 3/8" OD. These will fit typical openings designed for airlocks including bucket lid grommets, the larger nipple on a carboy cap, and drilled rubber stoppers.
NEW GUIDANCE: A customer asked about the oxygen that may be present in the fermenter headspace and whether it would contaminate the bladder bag. That's a great point and here's how we currently use our cold crash guardians. We roll up the bladder bag like an old tube of toothpaste and use a "chip clip" to hold it that way when we first tuck our fermenter away in the chamber. We come back after about one day of active fermentation and unclip the bag and let it unroll and inflate. By then, any oxygen that the yeast hasn't scavenged is long gone out through the blowoff and now any gas that fills the bladder should be CO2.
Typical solutions offered on brewing forums:
I just plug up my fermenter so that the vacuum cannot draw anything in.
If your fermenter can hold up to the vacuum without damage or sucking your stopper down the hole, the problem is that you will eventually need to unseal it. Once the stopper is removed, oxygen rich air gets drawn in. Also don't discount how damaging vacuum can be. You can crease PET fermenters this way. You can also implode stainless tanks.
I just use an S-style airlock because it will pass gas both directions without draining starsan back in.
The only problem this prevents is the contamination of beer with whatever liquid you have in the airlock. It does not stop oxygen.
Who cares if Starsan is drawn into the beer, it's safe enough to drink.
Wow. Most people immediately understand the lapse of judgement here. There are endless safe things you can add to your beer that would make it taste bad.
I never had a problem with contamination or oxidation.
Some beers are more or less susceptible to off flavors/oxidation problems and some people have higher thresholds for detecting those problems. If you are completely happy with your beer despite less than ideal practices, this product is not for you.
I hook up my CO2 tank and set it to less than 1 PSI to push in CO2 when the vacuum is formed.
This is indeed how the pros handle it and of course it works. At a homebrew scale there are a few things to keep in mind. First you do need a CO2 tank, a good regulator that doesn't drift, and a fermenter that is 100% sealed. If you have even a slow leak in the fermenter seals, kiss that whole tank of CO2 goodbye. If your regulator drifts even a couple PSI (due to being borrowed out of your cold kegerator), you can compromise your fermenters due to overpressurization.
Product Bulletin for Versions purchased prior to November 2018:
If your barbed tee looks like the one on the right with three barbs, please cut the last barb off as shown in the left side of the picture below. Inspect your bladder cap for splits/cracks before every use.