Hot-Side Aeration

Identifying that one problem, the thing responsible for the majority of brewing issues, is the dream of every brewer who knows that their beer is just one step away from greatness. And, for many brewers, hot-side aeration (HSA) becomes the boogeyman to conquer. Without smelling and tasting your beers, it is impossible for me to provide any definitive advice from my office perch. But I do have some thoughts that may help you in your brewing endeavors. And my first thought is that you should look beyond HSA.

Hot-side aeration refers to oxygen pick-up in mash and wort caused by splashing in the “hot side” of the brewery. Flavors that relate to HSA include wet paper (trans-2-nonenal), caramel/toffee, and Sherry; the typical buffet of oxidized beer flavors that may arise from enzymatic and non-enzymatic oxidation reactions.

The primary concern that commercial breweries, in particular those brewing very lightly colored and flavored beers, have with HSA begins with the malt. Very pale malts are made using gentle kilning methods that minimize color development and enzyme degradation. These types of malts may have lipoxygenase (LOX) levels that lead to lipid oxidation. The products of LOX activity survive wort production and can continue oxidative reactions in beer that lead the development of the classic wet paper aroma. Today, there are even LOX-less barley varieties being developed to eliminate this cascade of biochemical reactions from beer (for more on this, see “LOX-Less Malt” in the January-February 2019 issue). Fortunately for most home and craft brewers, higher kilning temperatures puts a real hurt on malt LOX levels and most of the base malts used by this group of brewers does not contain much LOX. Add to this the effect that mash temperature has on LOX stability and the fact that most home and craft brewers infusion mash at temperatures well above the ~ 122 °F (50 °C) sweet-spot for LOX activity, and it is reasonable to conclude that LOX activity is not a major concern for this group of brewers. LOX activity is not the only concern with HSA; non-enzymatic oxidation reactions do occur, but to a lesser extent due to process time and reaction rates.

The other thing to consider about HSA is scale, the source of much of the data about HSA, and how all of this relates to homebrewing. Research related to HSA, like almost all brewing research, was conducted by, and for, large-scale brewing. When large, commercial brewers talk about mash and wort splashing, they are talking about SPLASHING! Imagine an 8-in. pipe (200 mm) that is dropping mash at a rate of 450 gallons per minute (1,700 Lpm) 12 ft. (3.7 m) from the bottom of a mash mixer . . . by the time the mash hits the bottom it is traveling approximately 30 feet per second (9 m/s) or about 20 miles per hour (32 kph)! And that is just the beginning of splashing in brewhouses that were built before brewers figured out that all of this splashing was not ideal. Lauter tuns used to be filled from the top, and wort flowed from open grants into the kettles from the top. More splashing! The brewery engineers must have really been groovin’ to Bobby Darin’s “Splish-Splash.” My point is that the splashing you are seeing in your eBIAB is on a much smaller scale and is probably not the cause of your brewing ails. Not saying that HSA should be dismissed, but my beer gut always tells me that the best beers result from multiple right moves.

Now what? The root cause of the awful flavors that resulted in the drain pour could have been poor sanitation, contaminated yeast, insufficient yeast, low yeast pitching rate, improper wort aeration, lack of temperature control in fermentation, and countless other factors that cause flavor issues with beer. The key to efficient problem solving is knowing where to look. Even the best-equipped analytical brewing lab makes problem solving difficult to do if the analyst does not have an idea of where to begin. This is where sensory evaluation skills can really help point your nose in the right direction.

The key to efficient problem solving is knowing where to look.

I suggest that you invest in some sensory training to help guide your troubleshooting efforts in the future. You can take classes, for example at BYO’s Boot Camp, or enroll in the BJCP and Cicerone programs, read articles on the topic, use flavor standards to help train your senses, taste beer alongside of skilled tasters who can help guide you, and attend homebrew club meetings. The purpose of this training is to help develop a beer flavor vocabulary that ties to causation. For example, beers that have a spicy, clove-like aroma result from POF+ (phenolic off-flavor positive) yeast strains. If you like beers with this aroma and want to brew more beers with this character, seeking out POF+ yeast strains is something that will cut down on trial and error time. It could be that you don’t like the smell of cat urine on your beer.

What . . . cat urine? Yep. That aroma is found in certain hop varieties, most notably North American hops, and simply changing hop variety can be the silver bullet for that particular aroma. Whatever the flavor issue, sensory is a great starting point to help define what is happening.

Sitting at my keyboard without your beer to smell and taste does not allow me to identify the cause of your brewing woes. But hopefully this discussion has opened some doors about what you can do to become your own brewing detective, allowing you to hone your senses to help troubleshoot your future brews.

Response by Ashton Lewis.