Dear Mr. Wizard,

Regarding BYO’s response (twice) to Dan Cole of Roanoke, Va., (Mail, August ’98, March ’99) 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.

Andy Lynch and Bob Bratcher
Star City Brewers Guild
Roanoke, Va.

Mr. Wizard replies:

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.

Dear Mr. Wizard,

I have read several books and articles regarding mashing grains, but I am still not sure of the cause and effects on final flavor of different mash temperatures. Does a low temperature create a sweet beer? Does a high temperature create a dry beer? The answer to these questions always gets blurred through lengthy scientific explanations. Can you explain the cause and effect of mash temperature to this non-scientific brain?

Tom Flanders
Kensington, Md.

Mr. Wizard replies:

There is more to mash temperature than finished beer flavor. Mash temperature has an effect on wort viscosity and ease of lautering, it affects the gelatinization of starch ("melting" of the bonds that make starch a crystalline structure), influences wort fermentability, and has an effect on proteins. There are more factors that can be thrown in if decoction mashing and double mashing (the type used for beers like Bud) are considered and if you want to know about the addition of industrial enzymes.

Unfortunately, questions about mashing usually end up with lengthy explanations of all of this stuff, and the answers often raise more questions than they really answer.

The sweet beer/dry beer question focuses the discussion to one area, and that is the activity of two enzymes: alpha- and beta-amylase. The important thing to know about these enzymes is that they both attack starch but in different ways.

Starch comes in two forms. One form is called amylose (about 25 percent of barley malt starch) and contains no branches; it is simply a string of glucose molecules connected like links of a chain. The second form is called amylopectin (about 75 percent of barley malt starch), and this form does contain branches. Imagine a chain where one of the links is connected to two links and each one of these links is then connected to one other link. Now imagine this scheme where a new branch pops up after every 25 to 30 unbranched segments. The result is a complex structure originating from a single point. Think of a big oak tree with hundreds of branches. It might help to understand what follows if you draw a stick drawing of amylose and amylopectin.

Amylose and amylopectin have ends called reducing and non-reducing ends. The names are not that important, except that the ends of the branches in amylopectin are all non-reducing ends and its "trunk" is the only reducing end. Amylose is easy because it only has two ends, and one is reducing and the other is non-reducing. When either one of these molecules is split, there is a reducing and a non-reducing end formed.

Amylose and amylopectin are made up of chains of glucose, a simple sugar. They are the only two molecules that alpha- and beta-amylase do battle with in a mash. To get to the heart of the question, I need to give some basics on the two enzymes.

Beta-amylase: 1) has optimal enzyme activity between 140° and 149° F; 2) attacks chains of glucose from the non-reducing end only to form maltose, a simple sugar made up of two glucose molecules. Beta-amylase chews through a chain of amylose like Pac-Man eating dots two at a time; 3) can’t break a branch point in amylopectin; 4) is nicknamed the "fermentability" enzyme.

Alpha-amylase: 1) has optimal enzyme activity between 155° and 158° F; 2) randomly attacks chains of glucose and converts large molecules into a bunch of little chunks; 3) can’t break a branch point in amylopectin; 4) is nicknamed the "liquefaction" enzyme.

If you want a full beer with a low fermentability, steer your mash away from beta-amylase. This means mash in toward the upper end of the alpha-amylase temperature window and keep the mash as short as possible while still achieving a negative iodine reaction (no black-blue). Although alpha-amylase does manage to produce some fermentables due to its random activity on starch, the higher temperature minimizes the likelihood of rogue molecules of beta-amylase running around whacking off chunks of maltose from the non-reducing ends of starch molecules.

This is kind of like chopping veggies. If you don’t like small bits of evenly sliced carrots in your soup, don’t invite the local chef who goes chop-chop-chop at 120 chops a minute; instead invite the Boy Scout who goes whack-whack-whack and moves on to the next carrot.

One technique that will further cripple beta-amylase is a thin mash. Enzymes are more stable when they are latched onto their substrate (the substance they act upon), and a thin mash leaves a higher proportion of the enzymes floating around looking for their substrate. This is one of the reasons enzymes don’t have a single optimum temperature. In any case, if you use a thinner mash, you will produce fewer fermentables than in a thicker mash (up to a point — you gotta have water to make wort!).

If your objective is to make a very fermentable wort for a dry beer, things get a little more complex. For starters you really want beta-amylase to be a happy camper. Mash in cool, say around 140° F, and give your mash a good long hold. This will allow beta-amylase to chop up all the amylose and the tips of the amylopectin branches. This is a good start, but there are still a lot of glucose molecules tied up in amylopectin. The only way for beta-amylase to make more maltose is for alpha-amylase to "open-up" amylopectin molecules (the starch that has no branches) with a few random whacks.

If you wait around long enough, alpha-amylase will start to open up amylopectin. Remember, its optimum activity is around 158° F, but it still is active at cooler temperatures, though it’s much slower. As alpha-amylase opens up amylopectin, beta-amylase starts tearing into the new non-reducing ends and freeing more maltose. At the end of the "fermentability" rest, the mash should still be heated to around 158° F to achieve a negative iodine reaction. Bud Light is made using this type of mash profile, and the mash lasts for more than three hours. Unlike many other light beers, Bud Light wort has a low concentration of unfermentable carbohydrates and does not use exogenous enzymes (store-bought enzymes) in the process.

Another way to get alpha- and beta-amylase working together is to slowly increase the temperature from 140° F, after your initial 30- to 45-minute rest, to 155° to 158° F. This is easier said than done at home because small batches are harder to control than larger ones, but in commercial breweries using steam-heated, stirred mashes, this process is easy. The most common way of slowly increasing the temperature is to heat from 140° to 142° F and rest, then from 142° to 144° F and rest, and so on. This stair-step process is much easier to control than a continual rise from "A" to "B" because most mashing vessels are designed to heat at a constant rate and simply heating slower is not an option.

Stair-stepping can be done at home by carefully adding hot water a little at a time or alternating between heating steps and rests. The hard part is getting a good temperature reading while stirring and heating. If you are using gas or electric heat, don’t crank the burners up too high because temperature overshoot will most likely follow.

Some brewers do a bit of both. They mash in for a beta-amylase rest and then rapidly raise the temperature to the alpha-amylase rest to avoid too much dryness in the finished beer. Other beers mash in even cooler for beta-glucanase or limited protease activity. This is where the topic of mashing starts to get big.

One word of caution. Many brewers, when first starting out, get what seems like an ingenious idea that will not work. The idea is start out at 158° F to let alpha-amylase do its thing and then to cool the mash down to le beta-amylase do its thing. This won’t work because heat denatures enzymes at temperatures above their optimum, and denaturation is permanent. This idea does work in a decoction mash and in the American double mash because only a portion of the mash is boiled, but I’ll save that topic for another day!

Mr. Wizard, BYO's resident expert, is a leading authority in homebrewing whose identity, like the identity of all superheroes, must be kept confidential.