Terminal Gravity Woes, Hot-Side Aeration and Adding Water to a Boil

Can I add alpha amylase enzymes to my fermenter to help my beer attenuate? My original gravity (OG) was 1.079 and it has been two weeks. Now my beer is at 1.040 and is not showing any fermentation activity.

Paul Epp
Via email

Photo courtesy of Les Jorgenson

Alpha amylase can be added to the fermenter to aid in attenuation, but it has limited efficacy in converting dextrins and starch into fermentables. The primary role of the endoenzyme alpha amylase in the mash is as a debranching enzyme that chops up amylose and amylopectin into pieces from the interior of these molecules. Although alpha amylase does produce fermentable sugars, the yield of fermentables is better when beta amylase works alongside alpha. Before digging deeper into the enzyme rabbit-hole, let’s back up a few steps and talk about the factors that influence the final gravity of a batch of beer.

The OG of wort increases as “stuff” is dissolved in water during wort production. All-malt brewers dissolve this stuff from malt, and this stuff is primarily made up of fermentable sugars, unfermentable dextrins, starch bits that may not have been converted in mashing, and proteins. Brewers who use enzyme-free adjuncts, like rice and corn, also dissolve stuff, mainly carbohydrates, from these ingredients. And then there are ingredients in the “other” category that contribute fermentable sugars, unfermentable sugars, e.g., lactose, carbohydrate gums like beta-glucan, and myriad flavor compounds from the wide range of non-traditional ingredients used by brewers. Wort OG does not tell the brewer anything about how much stuff in the wort that drives OG is actually fermentable; OG is simply the density of wort before fermentation. Salt water’s density is greater than pure water, but is not fermentable. You get the point.

For the sake of discussion, let’s assume that a batch of wort was made with 60% non-enzymatic rice adjunct and 40% malted barley with a diastatic power (DP) of 135 °Lintner. Rice solids are approximately 90% starch, so most of the rice used in brewing can contribute fermentable extract. But enzymes are required for this to happen and in this example the enzyme package from the malted barley has been significantly diluted to ~54 °Lintner by the rice adjunct. The enzymatic threshold cited for functional conversion is about 60 °Lintner, depending on mash time and temperature, and this example describes a mash that is borderline enzymatically weak. This situation does not mean that the rice will not contribute extract, however, but it may result in decreased fermentability.

Given the details provided in most recipes, the FG can be approximate at best and, at times, not much more than a guesstimate . . .

Continuing down this path, how does a brewer know what to expect from wort in terms of FG (final gravity) when brewing a beer for the first or fiftieth time? Many homebrewers like brewing new beers on a regular basis and rely on a recipe for the expected FG. Given the details provided in most recipes, the FG can be approximate at best and, at times, not much more than a guesstimate added to a recipe that has never been brewed. However, if the recipe is something that is routinely brewed by a brewer, the FG value holds much more weight, especially if the ingredients used for the beer are consistent and if the brewer is not constantly adjusting the recipe. My point in relation to your problem is that you probably don’t know what the FG of your brew will be after fermentation is complete unless you have performed a forced fermentation test (aka an accelerated form of fermentation).

How can a recipe have a guesstimated FG if the recipe has never been brewed by the recipe’s author? As it turns out, most infusion-mashed worts have an apparent degree of fermentation (ADF) somewhere in the 70–75%, depending on the yeast(s) used for fermentation. For example, a 1.065 (16 °Plato) with an assumed ADF of 75% will finish at 1.016 (4 °Plato). This approximate value is useful when brewing a beer for the first time and also handy when trying to troubleshoot a problem. Your 1.079 (19 °Plato) wort should probably finish somewhere around 1.019 (4.75 °Plato). Assuming that you have produced a relatively “normal” wort in terms of ingredient selection and production method, your current gravity is quite a bit off the normal course.

The real question for you is “what’s the problem?” And the answer to this question likely lies on one of the following buckets: 1) yeast, 2) pre-fermentation preparation, and/or 3) wort properties. Here is a high-level view of what may be considered to help narrow things down:

• Did you pitch enough yeast? The rule of thumb for a 1.075 SG wort is somewhere in the 10–25 million cell/mL range. Higher gravity brews require more yeast than lower gravity brews.
• Was your yeast in good health when it was pitched?
• Is it possible that you are using a highly flocculent strain that dropped out early?
• Does your chosen strain do well in higher gravity fermentations?

Pre-Fermentation Preparation
• Was your wort properly aerated/oxygenated?
• Did you add yeast nutrients?
• Did you add a source of zinc?
• Did you cool the wort to the approximate fermentation temperature?
• Is the fermenter located in a stable environment with a relatively constant temperature?

Wort Properties
• Do you know what the actual FG should be?
• Is it possible that your wort is nutrient-poor?
• Did anything occur during mashing/wort preparation that makes you suspect that adding enzymes is going to fix the problem?

Unless you really diluted your malt enzyme package, used a boat-load of starchy adjuncts as steeping ingredients added to an extract wort, or mashed at a very high temperature (non-calibrated thermometer), I don’t think enzymes are your problem because your gravity is so off of the mark. If I had to place a bet on the root cause, I would place my wagers on yeast and wort zinc level. I am not going to address what you could have done differently before fermentation to address these issues because that is a separate question, so I will finish on what you may want to do to help your fermentation finish, and that is to kräusen your beer.

On the surface, kräusening is just a traditional method of carbonation. And in today’s world of brewing, traditional is oftentimes lumped into the bag of “boring tricks” that your grandfather used. But kräusening is much more than a carbonation method and is the perfect tool to dust off when fixing fermentation problems. The method is to make a “kräusen beer” that is about 15% of the volume of the beer being rescued. This kräusen beer can be different from the beer being kräusened; that’s OK if the blended recipe
is considered.

Kräusen beer is essentially a yeast starter that is added to beer after fermentation, or in mid-fermentation to stuck fermentations, for the purposes of carbonation and flavor maturation. Traditional lager brewers would add kräusen beer to the lagering tank, seal the tank up with a relief spunding/bunging valve, and allow the beer to carbonate and mature. Homebrewers can kräusen a batch without capturing the carbon dioxide if the goal is to simply help the fermentation finish and provide fresh, healthy yeast cells to clean up things at the end of the game.

If I were you, I would kräusen this batch before ever thinking about adding enzymes, unless I had a very good reason to suspect that the beer in my fermenter had a lower-than-usual wort ADF and that the enzyme treatment was more than a Hail Mary. By the way, granddad’s brewing toolbox had a lot of really cool and useful tools that the modern brewer should consider dusting off!

I have an electric Brew-In-A-Bag (eBIAB) system which is outfitted with a mesh basket to hold the grains for mashing. There is a center post in the basket with holes to recirculate the wort. These holes form a ring around the tube and there are several sets of these hole rings from the bottom to the top of the tube. My concern is when the basket is not full, the wort is sprayed out over the grain bed through the holes several inches above the surface. I have had several batches come out of primary fermentation with an awful smell and taste and had to dump the whole batch. Is my assumption that the wort is exposed to too much oxygen during the mash causing this off-flavor?

Mark Kutil
Germantown, Tennessee

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.

Brad Smith has stated a 90-minute boil is recommended for boiling off dimethyl sulfides (DMS). My pot is only 8 gallons (30 L) so 90 minutes results in too little wort into the fermenter. Is it OK to add water along the way during the boil?

Peter Young
Sault Sainte Marie, Michigan

Brewers, and those of us brewers who write about brewing, have all sorts of rules of thumb to help guide us through our brewing journeys. Boil time is one such rule. Some brewers say to boil for a least an hour to allow all of the things required in the boil to occur, and others skip straight to what works best for them and use that as their rule. Just guessing here, but Brad Smith probably has figured out that a 90-minute-long boil works best for his brews. A real dilemma with long boils, however, is excessive evaporation and energy consumption.

Adding water during the boil and/or at the end of the boil can certainly be done to help you hit your volume and gravity targets while hitting that 90-minute target. But long boils may do more than drive off DMS and water; they lead to flavor development, wort darkening, and contribute to beer oxidation through the creation of peroxide radicals that survive wort production.

As a starting point, you can slowly dial back the boil time if you are not having issues with DMS. At a minimum, you may be able to shave off a few minutes to your brewing day, and, in the process, you may discover that the shorter boil improves your beer flavor since different systems do better with different boil times.

Boil duration, intensity, and evaporation rate has been a topic of significant interest for the last 25+ years, and continues to be investigated because of the amount of energy consumed during this stage of the brewing process. Today, there are several high-temperature, thermal processing methods to sterilize wort, precipitate wort proteins and polyphenols, isomerize alpha acids, convert S-methylmethionine to DMS, and strip DMS from wort with either very minimal or no wort boiling. All of these methods incorporate some sort of wort stripping technique to remove DMS from the wort during the process and/or right before wort cooling. These methods will undoubtedly become more common in the future as concerns about energy consumption continue to intensify. Today’s rule of thumb may soon become another historical brewing technique.