Ask Mr. Wizard

Excessive Foaming Issues In Kegs


Cal Humrich — St. Thomas, Virgin Islands asks,

I’m kegging my ales and storing in a walk-in. I try to get the temperature as low as possible, but that’s just a bit above 40 °F (4 °C). some of the beers pour fine but some are super foamy. I’m assuming it’s probably the temperature (and need to revise my cooling system) but wondering if it is something else because with the problem kegs, they are foaming like crazy when I use the pressure relief valve. An example is as I release pressure with the split ring, gas is released, then nothing for a couple seconds then foam, and more foam, and more . . . I’ll leave the keg alone for a few hours (without gassing) and repeat the process. Eventually it will stop but it’s difficult to serve until it does. Any suggestions?


I agree with your suspicion that this problem may be related to temperature, especially if your walk-in cooler temperature swings up and down. A great start to troubleshooting would be to place a glass of water in the cooler and check the water temperature periodically over the course of a few days to determine the average along with the highs and lows. Because beer in a keg takes time to change, the glass of water should give you a good idea of the average temperature. Your system should be balanced based on your cooler temperature and you may discover that increasing your serving pressure and increasing the length of draft line solves the issue. But there are other things that can cause the foaming you describe.

One possibility is that your beer is slowly fermenting in the keg, becoming over-carbonated, and then foaming upon dispense. This is a simple explanation and one that is often rejected if it’s known that fermentation was complete before kegging. However, beer may referment in the presence of diastatic enzymes that slowly degrade unfermentable dextrins into fermentable sugars. Diastatic brewing yeast, like some saison yeast and Brettanomyces, are commonly associated with slow refermentation and can contaminate beer brewed with non-diastatic yeast through cleaning and sanitation failures.

The good news about diastatic yeast is that these critters are positive for the phenolic off-flavor gene, so-called POF+ yeast, and produce phenolic aromas that are easily detected simply by smelling. If you suspect POF+ yeast, the best thing to do is thoroughly clean your kegs and replace your draft lines. Brettanomyces is known to form biofilms; elbow grease and cleaning brushes help to remove biofilms and rid these unwanted yeasts from kegs and draft systems.

Late dry-hop additions can lead to hop creep where diastatic enzymes from hops cause similar problems as diastatic yeast. Hop creep may also show up in your beer’s aroma in the form of diacetyl. While there are different strategies used to prevent hop creep in dry-hopped beers, an extended rest after dry hopping is the most common method.

Diastatic yeast and hop creep cause overcarbonation. However, beer can uncontrollably foam when beer with a normal carbonation level is exposed to nucleation sites. Beer stone on keg spears, dirty draft lines, dirty beer faucets, and rough glassware are examples of surfaces that may cause beer to foam. Nucleation sites can also be present in beer.

The most extreme examples of gushing are associated with gushing proteins from malt. This is not a common problem and shows up when mold-contaminated barley, usually from Fusarium, is malted and later used in beer. The reason that this is not very common is that farmers and maltsters use measures to identify mold-contaminated barley and malt because there are legal limits on the amount of deoxynivalenol (DON), a specific mycotoxin, permitted in malt. However, gushing can occur even when DON levels are less than the 1 mg/L legal limit.

Calcium oxalate crystals are another example of a beer deposit that is associated with uncontrollable foaming. Calcium is present in wort and oxalate is present in malt. During the brewing process, most of the oxalate binds with calcium and is either retained in the spent grains or is precipitated as beer stone during wort boiling. If wort calcium levels are low, beer oxalate levels may rise and lead to the formation of oxalate crystal in packaged beer.

These crystals form slowly, and it may take several weeks for oxalate crystals to appear in unstable beers. While gushing proteins cannot be seen under a microscope, oxalate crystals are large and easy to identify because they have a distinctive shape and appearance. When oxalate crystals are observed in packaged beer the easiest way to reduce the concentration in future batches is to increase calcium additions during wort production, either by adding more calcium to the mash and/or adding calcium to the wort prior to boiling.

Beer haze may be the most vexing of brewing issues to  cope with but dealing with uncontrollable foaming can also be quite the beast. Hope you quickly nip this issue in the bud!

Response by Ashton Lewis.