Build your own blow off tube

Blow off tube. For more detailed pics, see slideshow below.

Every brewer likes to see strong fermentation in their beer; it means the yeast is healthy and doing its job, and the beer itself isn’t infected. But sometimes fermentation gets a little out of hand—so much so that it can cause a massive, worty mess that can even stain your ceilings unless you use a sufficiently large blow off tube.

 

There are a lot of factors that determine how fast the fermentation takes place. Beer style, pitching temperature, and yeast starter size are a few of these factors. Also, if you like to recycle yeast by pitching wort on top of a yeast cake from a previous beer, you are more likely to have problems with vigorous fermentation. 

 

How does this become a problem? Krausen, foam that forms on top of fermenting beer, can build up too high and push matter into the airlock. Once the airlock is clogged, it will no longer let C02 escape, and the pressure builds until a Mount Vesuvius-type event occurs. 

 

The solution is simple, though. Many homebrewers prevent this problem by using a blow off tube instead of a traditional airlock. Blow off tubes are quite easy to build yourself, and the supplies are fairly inexpensive. Here are a few factors to keep in mind: you will need a blow off tube that will fit well on your carboy, be easy to handle, and not be easily plugged. 

 

While you can fit a blow off tube on your carboy cap, you can also find a hose of sufficient size to fit on the carboy without having to use the cap. You won’t need an airlock in addition to the blow off tube—the tube is a sufficient air lock. 

 

Stephen Small details how to make a “Big Bore Blow Off Tube” on his website.

 We assembled one using Small’s advice. To make your own like this one, you will need appropriately-sized food-grade tubing (avoid tubing that might impart flavors to your beer) and 2 PVC elbows.

 

Measure the inside of your carboy. This measurement will be the outside diameter of the tubing you need. We found 1 3/8” OD braided tubing at Home Depot. You will need enough length for three pieces: one to come vertically out of the carboy, one to go horizontally from the center of the carboy past the edge of the carboy, and one to go down from the top piece to the bottom of the carboy. Don’t short yourself on the length—add an extra foot or so just in case. The tubing is the most expensive part of the setup, so spending a little time figuring lengths could save you money in the end. The PVC elbows need to fit snugly inside the tubing. We used 1/2” elbows with our tubing.

 

Once you have the tubing and elbows, all you need to do is cut the tubing into the three pieces and fit them onto the elbows and into the carboy neck. Remember, the end of the tubing needs to fit into some vessel filled with water or sanitizer to maintain an airlock. (We use a tall, narrow glass positioned in another vessel so it won’t tip over.) Cut that piece of tubing long enough so that it will easily stay under the level of the fluid. Tubing has a tendency to curve and warp, so you may need to some extra length to account for that. The lengths of tubing we used are approximately 3.5”, 5”, and 17”, but you may find slightly different lengths more suited for your setup.  

 

Before using your blow off tube, remember to sanitize it. During use, periodically check the level of fluid in the vessel to make sure the tube is still immersed. 

 

Now, you can relax and watch the fermentation bubble away like crazy without having to worry about cleaning it off your ceiling.