Bulk lagering vs. package aging, NABLABs, storing kegs & scrubbing dissolved oxygen
Q. How does lagering a beer in a carboy or barrel affect the beer differently than storing the same unfiltered beer in a bottle or keg at the same temperature for the same period of time?
Chris Patterson
Downers Grove, Illinois
A. This is a great question, Chris, and the answer starts with a quick review of the objectives of lagering. Although lagering is most often associated with lager beer, the process can be applied to all types of beer. Some brewers refer to all aging processes as “lagering,” others use the term “cellaring,” and some simply say “aging.” Naming aside, yeast sedimentation, diacetyl and acetaldehyde reduction, flavor integration, and sulfur scrubbing are among the key changes in beer flavor and appearance that can occur during lagering. In the commercial lager world, lagering may also include partial or complete natural carbonation.
Cask conditioning, while rooted in ale tradition, shares much in common with lagering. One of the key differences between lagering and cask conditioning is volume: Lagering is a bulk process in which the finished beer is later transferred to kegs, bottles, or cans, while cask ales are conditioned in the very vessels from which they are served. Another difference is yeast sediment. Commercially packaged lagers typically do not contain yeast sediment, whereas cask ales generally do.
At home, lagering can be done in containers that do not permit carbonation, such as carboys, or in containers that do, such as kegs or certain pressure-rated small fermenters (such as those included in this homebrew unitank comparison). In both cases, beer clarification, flavor maturation, and sulfur volatilization occur. Lagering in a keg allows homebrewers to mimic commercial practices, including kräusening — adding actively fermenting beer to fully fermented beer to achieve carbonation and speed aging. A key part of this process is venting excess gas. While aging in a carboy also allows sulfur venting, keg aging, where CO₂ is naturally produced and released, is my preferred method.
When lagers are aged in bottles, three important things cannot occur: Sulfur scrubbing, yeast sedimentation, and yeast separation. A practical solution for home lager production is to select a yeast strain that produces clean, low-sulfur lagers within a short fermentation and maturation window. Strains such as SafLager W-34/70 can be used successfully at warmer temperatures (59–68 °F / 15–20 °C) by both home and commercial brewers to quickly produce beers with low diacetyl and sulfur. Others, such as LalBrew NovaLager, have been developed through traditional selection and hybridization to yield strains that produce minimal diacetyl and hydrogen sulfide.
As long as the beer is cooled to encourage most yeast to drop out before packaging, you can bottle-condition and age for flavor integration. Is the result identical to bulk-aged lager? Probably not, but it can be surprisingly close.
Q. I have been looking for maltose- and maltotriose-negative yeast to brew a low-alcohol Pilsner recipe from BYO. The yeast recommended is White Labs WLP603 (Torulaspora delbrueckii) or SafAle LA-01, and I can’t find those yeasts in a homebrew size. Every maltose-negative yeast is either the 500-g size or unavailable through any online retailer or homebrew shop I have searched. Any tips on what homebrewers can do?
Mike Seward
Barrington, Rhode Island
A. Before I answer this question, I want to say that I sometimes sit on questions because great questions come in waves and this one was sent into the mailbox earlier this year. It’s rarely the case where new information comes about while questions sit in the inbox, but in this case the body of knowledge related to non-alcoholic (NA) brewing is growing at a rapid pace. Bottom line is that this is a timely question and I have some thoughts about this topic.
I am not surprised that you haven’t been able to find a source for these yeast strains because none of these suppliers are selling them into homebrew markets. There is one major challenge when brewing beer with maltose- and maltotriose-negative yeast strains, simply referred to as maltose-negative strains; the biggest risk to stability comes from garden-variety brewing yeast.
Because breweries, both home and commercial, are rife with brewing yeast, the risk of contamination is high. When beer produced using a maltose-negative strain is contaminated with a regular brewing strain, over-carbonation and the possibility of exploding packages is a clear and present danger. The only currently acceptable stabilization process is pasteurization. This may change in the future as alternative approaches are examined, but those currently do not exist. Some breweries and research facilities are serving unpasteurized NA beers fermented with maltose-negative yeast in dedicated draft systems where temperature control is used to minimize the risk of re-fermentation and monitoring is used to check for the signs of re-fermentation.
Another concern with NA beers is the growth of pathogens. That’s the other reason that commercially produced NAs are pasteurized. I will come back to this topic later but want to pivot to some other points first.
If I were writing this answer earlier this year, I probably would not have thought much about the actual alcohol content of the beer as a real concern to homebrewers. However, the alcohol content of these beers is of concern to many of the people who drink them. The term NABLAB is used around the world these days to describe non-alcoholic and low-alcohol beers. Although definitions are not universal, most countries define beers with ABVs between 0.5 and 2.5% as “low alcohol.” When alcohol is less than 0.5% ABV, the term “non-alcoholic beer” is used. The term “alcohol-free” or “zero-alcohol” is reserved for beers with no measurable alcohol.
Consumers who are serious about how they consume or do not consume alcohol must be able to rely upon the producers of NABLABs to properly adhere to these product classifications. Because I drink beer, I am one of those consumers who is not overly concerned about drinking something that may contain 0.7% ABV instead of 0.4% ABV. But brewers cannot make assumptions about others and need to be precise with labeling. If your interest in brewing NA at home is related to brewing beer for a friend or loved one who cannot or does not want to consume alcohol, you really should stick to purchasing these beers from a commercial producer unless you are willing to have your beer analyzed before serving.
You specifically asked about using maltose-negative yeast because that is the method discussed in Kara Taylor’s article. However, there is another method available to homebrewers that does not require special yeast or equipment — high temperature mashing. This method involves mashing in at ~176 °F/80 °C, resting for about 15 minutes, collecting, boiling, and cooling wort as usual, and fermenting with whatever yeast strain you want to use. Because there is essentially no beta-amylase activity, very little if any fermentable sugars are produced during the mash. This very high temperature also quickly stops alpha-amylase activity and results in starchy wort. Halting alpha-amylase is important because alpha-amylase does produce some glucose, maltose, and maltotriose because its action on starch is random.
I recently brewed two beers using this method. Although I knew what I was doing, I was still surprised by the cloudiness of the wort. Not seeing anything during fermentation, although not surprising, was also odd. Although there are compounds in wort that yeast metabolize during the short fermentation, the lack of appreciable fermentable sugars means that alcohol production is all but eliminated and the fermentation appears non-existent. While the beers both finished with a veil, neither are extremely hazy.
Much of the focus of NABLAB production is aimed to eliminate worty aromas and flavors common to these beers. One method that works surprisingly well is kettle souring. Lactic acid bacteria apparently metabolize some of the worty precursors and reduce the concentration of aldehydes in the finished beer. And the interesting thing is that this action occurs in kettle soured wort that is not obviously sour. This means that pH can be monitored and the process stopped with wort boiling before the wort is sour, allowing the method to be used in just about any style.
My recent NA brews used kettle souring. In one brew, a Pilsner-style NA, I dropped the pH to 3.9 (my target was 4.0) and in the second brew, the base for a berry-flavored sour, I dropped it all the way down to 3.2. I used kettle souring in an attempt to reduce worty aromas — this was a success — and to lower pH for safety reasons discussed later.
The 2025 Summit — a joint conference uniting members of the American Society of Brewing Chemist (ASBC) and the Master Brewers Association of the Americas (MBAA) — featured numerous presentations related to NABLAB production. The one topic related to NABLABs that has brewers and industry experts concerned is the risk posed by spoilage and pathogenic microorganisms, especially when it comes to draft beer. Because in-keg pasteurization is not possible and the very real challenges associated with properly cleaning and sanitizing kegs, keg couplers, and draft lines, many brewing experts and brewers believe that NABLABs should only be served from cans or bottles. Although some brewers are conducting research into the use of liquid preservatives, in-package pasteurization is the only preservation method universally accepted for these beverages.
Some small-scale producers use batch pasteurization to process cans and bottles of NABLABs. I can address that process in another column, but for the time being I will just leave you with the knowledge that batch pasteurization is something that can be performed at home. A very conservative level of batch pasteurization for a typical NABLAB is in the 80–120 PU range.
Whether producing low-fermentable wort using the hot and fast mash method or using a maltose-negative yeast strain, I believe that certain practices should always be followed brewers, and others should be avoided when producing NABLABs.
DO:
- Boil wort for at least 30 minutes
- Heat-sanitize the wort cooler
- Reduce wort pH to <4.2
- Adjust finished beer pH to <4.2, if required
- Add all hops before wort cooling
- Heat-pasteurize finished product
DO NOT:
- Dry hop — this simply is an unnecessary risk
- Add unpasteurized fruit purees or any fermentable sugars if your goal is <0.5% ABV
- Barrel age
I know that commercial craft brewers read this column. If you are one, know that I am a big proponent of this growing category of beer. I sincerely want brewers to continue elevating these beers without incident. It’s really amazing how many excellent-tasting products are currently being produced. Brewers are going to do whatever because these products are only regulated by the TTB and the industry does not want to see that change — that’s why producers of these products are so concerned about possible issues in the market.
Caution flags and raised voices, however, will not prevent brewers from experimenting with these beers at home and taking the easy way out by packaging in kegs and not pasteurizing. If you decide to roll the dice, read the literature, understand the risks, clean your kegs by completely disassembling, sanitize your kegs after reassembly, use new draft lines and picnic taps, and store your keg and dispense rig in a cooler at <38 °F/3.3 °C. Finally, have a party and drain the keg asap.
Q. I have a question about storing kegs after they’ve been cleaned and sanitized. I had a bad experience when I had purged a keg with CO2 and stored it that way for months before using it for kegging. On the day we were going to keg, I popped the lid and got a very strong, pungent odor from the keg. I would say it was even acidic, as if carbonic acid gas had formed over time. How could this have happened? Perhaps I left too much sanitizer in the keg, though I do my best not to do that. Or maybe some other contaminant was present because I didn’t clean well enough? Or perhaps this is a natural process that occurs over several months and the long-term storage of kegs needs to be done differently?
Jeff Vandewinckel
Arlington, Tennessee
A. Your example is an extreme case between sanitizing and use, but the broader question is one I’ve often heard craft brewers discuss when preparing equipment. My preferred method is to clean equipment immediately after use, then sanitize just before use. Fermentation vessels, for instance, are easiest to clean shortly after emptying. Often, a simple water rinse with gentle scrubbing, followed by another light rinse and then a cleaning cycle — either by hand or with a pump and spray ball — is quick and effective. Some brewers then sanitize the vessel and store it closed and under pressure until needed, as you describe.
The real issue with cleaning and sanitizing is that neither process is absolute — sanitized equipment is not sterile. And because no-rinse sanitizers used in brewing and food processing rarely provide residual activity, any surviving microorganisms can grow if nutrients are present. It’s impossible to know exactly what developed in your keg during extended storage, but the sour smell is a clear indicator that something did. Carbonic acid itself is odorless, but when you sniff carbonated beverages, it creates a tingling sensation in your nose. By contrast, organic acids such as acetic, propionic, and butyric have sharp aromas that are easy to detect.
Going forward, I recommend cleaning equipment immediately after use, allowing it to drain, and then storing it. Dust is difficult to control at home and can carry yeasts, molds, and bacteria. A quick rinse followed by sanitization right before use is the best practice.
Q. Can I put ascorbic acid in my cans before I fill them with beer to scrub any dissolved oxygen? Also, how would I dose it?
Darren O’Day
Philadelphia, Pennsylvania
A. Ascorbic acid, also known as Vitamin C, is indeed an antioxidant often discussed in the context of beer stability because of its ability to scavenge oxygen in the headspace of packaged beer. Its mode of action is somewhat different from many other antioxidants. Ascorbic acid does not directly bind oxygen. Instead, it donates hydrogen atoms to reactive oxygen species such as peroxide radicals, thereby neutralizing them. This transfer of electrons is the fundamental chemical process we call oxidation.
However, the behavior of ascorbic acid can be complicated by the presence of transition metal ions, particularly iron and copper (Fe²+ and Cu²+). In the presence of these metals, ascorbic acid can actually promote the generation of reactive oxygen species rather than prevent it, effectively reversing its antioxidant role and causing oxidative damage. For this reason, successful use of ascorbic acid requires very low levels of these metal ions. Unfortunately, in brewing, keeping metals out can be difficult. Common brewing inputs such as hops, malt, brewing water, and filtration aids can all be sources of copper and iron. But for the sake of discussion, let’s assume a beer with minimal problematic metal ion content.
When used under the right conditions, ascorbic acid is safe for beer, though flavor limits must be respected. At higher concentrations, it imparts a noticeable tartness. The threshold for this effect varies depending on beer style: Light, delicate beers can show tartness at concentrations above about 10 mg/L, while more flavorful or heavily hopped beers can tolerate slightly higher levels. As is often the case in brewing, bench trials are invaluable for determining the appropriate dosage for a specific recipe. A common working range is 5–10 mg/L.
The most practical way to add ascorbic acid is as an aqueous solution. Because the compound itself is reactive toward oxygen, the solution should be prepared in deoxygenated water — ideally water that has been boiled, cooled, and stored in a sealed container to minimize oxygen pickup.
The dosage calculation is straightforward when using metric measurements. For example, suppose you are working with 20 liters of beer and wish to dose at 10 mg/L. That requires 200 mg of ascorbic acid in total. Since the solubility of ascorbic acid in water at 68 °F (20 °C) is about 330 g/L, there is no risk of creating an overly concentrated stock solution. A convenient approach is to prepare a 40 g/L stock solution. 20 mL of this solution will contain the required 200 mg of ascorbic acid for the 20-L batch. Unless you have a highly accurate scale, mixing up 4 g of ascorbic acid in 100 mL of water is easy to measure and gives you plenty for bench trialing and dosing.
