Hot Side Aeration Debate
TroubleShooting
Andy Lynch and Bob Bratcher • Roanoke, Virginia asks,
Regarding BYO’s response to Dan Cole of Roanoke, Va. about hot-side aeration; I know Dan and he is not given to asking contentious questions for the sake of being contentious. I think he has intelligently challenged you to answer a simple question with a real answer. You have twice told him that HSA is not a problem for homebrewers, but you have never given a researched or referenced answer as to why you believe this. Perhaps most brewers do have a lot to worry about before HSA ranks on their list of problems. Some never get to the level of experience and scope of brewing where it may be an issue. However, as a subscriber, I feel a better answer to the question is called for. A little explanation as to why the editor disagrees so strongly with Mr. Wizard as well as your other feature writers would go a long way to settle this question.
Before I jump head first into this colorful debate about hot-side aeration (HSA), I would like to explain where some of the comments in BYO mail and in some of the BYO articles stem. Most of the comments regarding this whole debate have come from commercial brewers who write for BYO. To paraphrase, they have suggested to our readers not to worry about HSA too much because there are bigger problems to solve. Steve Parkes wrote that “the English homebrewer is more likely to be opening a can of extract…than worrying about excessive wort splashing causing hot-side aeration” (“Brewing Like the British,” December ’98 BYO). Some readers might have thought Parkes was saying that splashing hot wort could cause HSA, but I think his point was that American homebrewers tend to worry about things more than the English.
Dan Cole has asked for an experiment conducted by a third party to confirm or deny the existence of hot-side aeration. This would be a great experiment if the topic were new. Fortunately for those interested in HSA, it is a well-researched topic and the research conducted over the years clearly shows that oxygen pick-up during mashing and mash transfer has an effect on beer flavor.
The topic of HSA can be divided into two are as: 1) aeration prior to wort boiling and 2) aeration after wort boiling. Malt enzymes, such as lipoxygenases and polyphenol-oxidases, that catalyze oxidation reactions are present in the mash and wort prior to wort boiling. In my opinion, this is where the HSA concern makes sense.
The second class of HSA is wort aeration after boiling. The only real consequence I have seen cited about aeration after the boil is an increase in wort color. Keep in mind that very hot wort, wort right after the boil, does not permit much oxygen into solution and under normal brewery conditions this probably won’t cause much wort darkening.
Anheuser-Busch (A-B) uses a device called a volatile stripper that forces hot air over thin films of wort after wort boiling to remove undesirable aromas such as DMS (dimethyl sulfide, which smells like cooked corn). Although A-B has adopted the philosophy of minimizing oxygen pick-up during mashing, mash transfer, and wort collection, the company still uses the wort stripper to make very pale-colored beers.
Personally, I believe the body of scientific evidence surrounding HSA in relation to mash and wort oxidation prior to boiling is believable. Luckily, the problem is easy to control. Basically, don’t splash too much during mash-in, transfer from the mash pot to the lauter tun, and wort collection. This seems so simple that most people don’t see the big dilemma.
Every serious homebrewer needs to visit an old brewhouse for a different perspective. Many older mash mixers used in commercial breweries had large baffles to aid in mixing. These baffles cause a lot of splashing, especially if the mash agitator is moving very quickly. Next the mash was pumped to the lauter tun. Almost every lauter tun built prior to 1970 was filled from the top. This literally resulted in mash being dropped at a high velocity from about five feet from the false bottom during filling — lots of splashing! Finally the wort was typically pumped into the top of the brew kettle, where it would cascade up to 20 feet to the kettle bottom, resulting in yet more splashing.
Today, mash mixers are designed with special agitator blades to minimize splashing during mash heating. Lauter tuns are filled from the bottom to ensure a very quiet fill. Some experimental lauter tuns even operate under a slight overpressure from carbon dioxide. New brew kettles are filled from the bottom, and the worry about splashing has been designed out of the modern brewhouse. Even the beautiful and traditional wort grant has been replaced by wort collection piping systems that eliminate any exposure of wort to oxygen during transfer from the lauter tun to the brew kettle. After wort boiling, most breweries use whirlpool vessels to separate hops and trub from wort, and even these vessels are constructed to minimize splashing during filling.
As long as homebrewers exercise a little care, the likelihood of having HSA problems is very slim. The truth is that commercial brewers are concerned about HSA and that companies that manufacture brewhouse equipment have responded to these concerns by changing their designs of the past.
The confusing part for the homebrewer is that many writers who write for homebrew publications also work in the commercial-brewing arena, and commercial-brewing concerns frequently become homebrew concerns. Unfortunately, Mr. Cole felt like he was being brushed off by past comments stating that HSA is not much of a problem for the homebrewer. For what it is worth, I don’t feel that HSA is a huge issue for most homebrewers. However, for those inquisitive homebrewers such as Mr. Cole, HSA is an interesting topic.
