Producing high-quality nonalcoholic (NA) beer has involved tradeoffs among flavor, cost, and process complexity. Traditional methods, such as arrested fermentation or mechanical dealcoholization, often result in an unappealing “worty” character, or they strip away the volatile flavor compounds essential for a typical beer profile. Specialized maltose-negative yeast strains have emerged as a compelling alternative because they inherently produce less ethanol by consuming only simple sugars. However, many currently available strains are undomesticated wild isolates that lack the refined traits of traditional brewer’s yeast, often leading to undesirable off-flavors.
Making a high-quality NA beer requires domesticated traits that allow for proper fermentation chemistry, the absence of wild off-flavors, and process efficiencies. Here we explore how Berkeley Yeast has addressed these challenges by developing maltose-negative NA strains from a domesticated industrial brewer’s yeast, thereby retaining the performance benefits gained through centuries of trait selection by brewers.
Figure 1. Berkeley’s strains make NA beer with the same beer flavor and process efficiencies as traditional brewer’s yeast.
Overview of Methods for Making NA Beer
Before we dive into the world of maltose-negative brewer’s yeast, let’s start with some context. Across the industry, there are several methods for producing NA beer, each with its own trade-offs in flavor, cost, and process complexity.
One method is arrested fermentation, brewing a low-gravity beer and fermenting with standard yeast but stopping the fermentation early so only a small fraction of sugars is converted to ethanol. The result is low alcohol, but also a product that retains a lot of wort character. These beers often don’t taste like a typical finished beer because the yeast doesn’t get the chance to do its full fermentation chemistry (more on that below).
Another widely used method is dilution: brew a full-strength beer, then dilute it. The major advantage here is that you get none of the worty character associated with arrested fermentation. The drawback is that the dilution step tends to thin out the body and flavor, often landing closer to beer-flavored sparkling water than beer.
Recently, a number of products have used mechanical dealcoholization. These processes—which include vacuum distillation and membrane filtration—allow for full fermentation, and no dilution is required. However, these processes not only strip out ethanol, but they also strip out volatile flavor compounds that are critical for normal beer quality and flavor. To compensate, producers often add back beer-flavored natural flavors. The results can be impressive, but they also come with challenges. They rely on expensive equipment with a physical footprint, and they require an additional processing step, with all the logistical, maintenance, and energy cost that comes with it. If natural flavors are added to restore beer flavor, there are additional challenges associated with formulation, sourcing, and QC, and their addition precludes a “clean label.”
More recently, specialized yeast has emerged as a compelling alternative. Instead of arresting fermentation or removing alcohol after the fact, these strains inherently produce less ethanol. Most of these strains are “maltose-negative,” meaning that they don’t metabolize maltose—the primary sugar in wort—and instead consume only simpler sugars such as glucose. With a couple of tweaks to a standard beer recipe, these yeast strains produce about 15 percent of the ethanol. Before Berkeley Yeast, the strains available to brewers were wild isolates and hybrids, not the yeast strains domesticated by brewers for brewing. NA beer made using undomesticated strains has less of the beer flavor and quality that you get with standard brewing and more of the genetic baggage from undomesticated yeast. In contrast, Berkeley Yeast strains were developed from standard brewer’s yeast to retain all the qualities that result in the beer flavor and quality that generations of brewers have painstakingly optimized and maintained, except without the ethanol production.
Understanding the Challenges with Maltose-Negative Yeast
Maltose-negative yeast aren’t new. In fact, it’s just the opposite: Most undomesticated yeast strains don’t efficiently consume maltose. It wasn’t until humans settled down and began cultivating maltose-rich cereal crops and using them to make beer that brewers’ yeast strains were domesticated for efficient maltose consumption. Indeed, the coevolution of brewer’s yeast with human civilization has imposed a remarkable genetic selective pressure and has made modern brewer’s yeast particularly well suited for producing beer. This is “domestication” in action, the process by which humans selectively manage biological organisms, leading to genetic changes that make the organisms more useful to people.
Most maltose-negative strains that are marketed for making NA beer weren’t domesticated for brewing. This presents a major challenge for brewers because the strains lack the traits that are key for achieving the signature flavor and quality of full-strength beer and for making the brewing process practical and efficient. The effects of domestication are wide ranging but generally fall into three categories: normal fermentation chemistry, low wild yeast off-flavor compounds, and process efficiency traits. Let’s look at each of these.
Normal Fermentation Chemistry
Through domestication, yeast was selected to make key beer-flavored compounds, such as esters, and to reduce certain undesirable compounds present in wort, such as aldehydes.
Esters are the most prominent class of beer-flavor compounds. They are desirable because they are perceived as fruity. There are a few esters in particular that are most reminiscent of beer:
- Isoamyl acetate tastes like banana;
- Ethyl acetate tastes like melon and solvent (desirable at low levels);
- Ethyl hexanoate tastes like pineapple.
In combination, these esters are at the core of what makes beer taste like beer.
Aldehydes, on the other hand, are associated with undesirable worty flavors. They must be reduced to imperceptibly low levels during fermentation to make a palatable beer.
Undomesticated maltose-negative strains have not been selected to do the normal fermentation chemistry. This results in a deficiency in both the production of esters and the reduction of aldehydes. Most undomesticated maltose-negative strains don’t produce enough ester character and are incapable of reducing aldehydes to ultra-low levels, so when using these strains, you can end up with a product that tastes less like beer and more like wort.
Low Wild Yeast Off-Flavor Compounds
Industrial strains that were domesticated for brewing were selected to make palatable beer, with ultra-low levels of off-flavors. The undomesticated ancestor of brewer’s yeast produced a variety of unpalatable off-flavor compounds that include
- short-chain fatty acids that carry aromas of cheese and smelly socks;
- phenolic compounds that contribute plastic and medicinal notes;
- high levels of ethyl acetate, which at elevated levels is perceived as nail-polish remover.
You may have experienced these different off-flavors in contaminated homebrew and some spontaneously fermented beers and wines. These flavors are also commonly produced, to varying levels, by naturally occurring maltose-negative yeast strains that are now used for NA brewing.
Process Efficiency Traits
Over time, brewer’s yeast strains were selected for traits that made them more efficient for beer production. Two key features of domesticated brewer’s yeast are its ability to rapidly consume sugar and its ability to flocculate after reaching terminal gravity.
Brewer’s yeast strains became very efficient at rapidly metabolizing the major fermentable sugars in barley—maltose, maltotriose, and glucose. While maltose-negative strains consume only glucose, the rate of its consumption is especially important in NA brewing because some maltose-positive Saccharomyces may be present at trace levels in a production brewery. If the NA tank is warm for long enough, you run the risk of a house strain fermenting the maltose and maltotriose and taking the beer out of spec. Therefore, the goal for fermentation is to proceed quickly and finish within the first 48 hours. Most wild yeast strains consume glucose slowly, taking longer to hit terminal gravity.
Brewer’s yeast’s ability to flocculate makes the yeast separation process easier. Removing yeast before pasteurization of NA beer is paramount because off-flavor compounds associated with autolysis can be released if yeast is left in suspension. Most wild yeast strains don’t readily flocculate in standard brewing conditions.
The key takeaway here is that through domestication, brewer’s yeast strains have been selected for many traits that make them uniquely suited for brewing, and these traits remain important for NA brewing. The process of trait selection and domestication by brewers occurred over centuries. In contrast, if you brew with an undomesticated maltose-negative yeast, while the product may be low ABV, it will taste less like a traditional beer.
Maltose-Negative Yeast with the Benefits of Brewer’s Yeast
Figure 2. Berkeley’s strains check all the boxes, producing NA beer that tastes more like actual beer, while retaining the characteristics brewers have selected for over the centuries.
So, how did Berkeley Yeast make a maltose-negative yeast strain with low ethanol production that also has the desirable qualities of a brewer's yeast? Instead of asking a wild maltose-negative yeast to do a job it wasn’t bred for, we started with a brewer’s yeast that was bred specifically for brewing and made it maltose-negative. As a result, Berkeley Yeast strains behave like traditional brewer’s yeast, minus the ethanol production. So, you can brew NA beer just like you brew all your other beers.
Restoring Fermentation Chemistry
With this approach, there is one major caveat that we had to address: When you remove the maltose-utilization trait, the yeast consumes only about 15 percent of the fermentable sugar. This reduces the overall amount of fermentation chemistry that the yeast does. We found that if you don’t restore the fermentation chemistry, you get too little beer flavor and too much wort character. With the Berkeley Yeast NA strains, we were able to restore the fermentation chemistry to 100 percent. This allowed us to develop a series of NA yeast strains with all the benefits of traditional brewer’s yeast and none of the baggage from wild yeast.
Figure 3. Berkeley Yeast strains restore full fermentation chemistry.
What exactly do we mean by “restore fermentation chemistry”? First, let’s talk about esters. Esters are beer-famous for the major impact they have on beer flavor. Isoamyl acetate, in particular, is one of the most important and well-studied compounds. Figure 3, top left, shows the key biochemical pathways involved in brewer’s yeast. In ester biosynthesis, yeast generates isoamyl acetate from two converging metabolic pathways—the “isoamyl” comes from leucine metabolism through the Ehrlich pathway, and the “acetate” comes from sugar metabolism, through the glycolysis pathway.
Isoamyl acetate’s sweet spot is about 1,000 µg/L. If you have much less, the flavor impact may be difficult to detect. If you have much more, it can be unpleasant. When we first removed the maltose-utilization trait, we expected the esters would be reduced in proportion to the reduced attenuation. We reasoned that less sugar going in would mean less flavor coming out. But we were surprised to see that there was much less ester production, about 50 times less! But with some genetic tweaks, we were able to restore esters to their sweet-spot levels (Figure 3, top right).
Note that the “sweet spot” for isoamyl acetate depends on the matrix. In a NA hazy IPA, 1,000 µg/L provides a nice and fruity character. In a light NA lager, the sweet spot is considerably lower, and Berkeley’s strains are dialed in accordingly.
Next, let’s talk about aldehydes. Wort is naturally very high in aldehydes, and these compounds are a key driver of worty flavor. Brewer’s yeast strains are very efficient at reducing these aldehydes during fermentation, which is a big part of why a full-strength beer doesn’t taste the slightest bit worty. This is important because if these aldehydes aren’t reduced during fermentation and they make it through to the finished beer, the worty flavors that come through can be very damaging to the finished product. For example, the most prominent aldehyde in NA beer is methional. If you’ve ever cracked an NA beer and tasted boiled potatoes, cooked vegetables, or canned tomatoes, then you’re familiar with methional. You can try to mask the aldehydes with natural flavors, but the added flavors can push the product away from your target.
The lower half of Figure 3 shows how Berkeley Yeast NA strains consume methional during fermentation and reduce worty-tasting aldehydes such as methional to flavorless products. The Berkeley Yeast strains exhibit similarly reduced levels of aldehydes as in full-strength beer fermented with standard brewer’s yeast. No need to restore key volatiles with natural flavors. No need to mask off-flavors.
So these strains look good on paper. But how about outside our lab, compared to other commercially available NA strains? In 2025, a team of researchers led by Scott Lafontaine at the University of Arkansas conducted a seminal study (Maust et al.), comparing the performance and sensory outcomes of 11 commercial NA brewer’s yeast strains. Generally speaking, the Berkeley Yeast strains were rated as producing NA beer that tastes more like an actual beer, with some of the other commercial strains producing plastic, cheesy, and solvent notes.
Figure 4. Sensory ratings of NA beer made with Berkeley Yeast and various commercially available undomesticated yeast strains. The orthonasal sensory ratings for the beers fermented with the strains tested in Maust et al. were plotted, with the Berkeley strains in the left column of each graph, and the other strains in the right column.
But the thing we find most impressive is the significantly reduced wort character in beers made with the Berkeley strains. As shown in Figure 4, the three descriptors most closely linked to wort character were near-zero for the Berkeley samples, in contrast to the significantly higher ratings for the others. No wonder the beer tastes better!
Avoiding the Wild Off-Flavors
Making a good NA beer is not just about doing the right chemistry (i.e. producing esters, reducing aldehydes), but it’s also about not doing the wrong chemistry. In the wide world of yeast, there are lots of maltose-negative strains; however, because they weren’t selected and domesticated for brewing, they typically produce flavor compounds that don’t taste good in most traditional beer styles.
When we developed our NA strains, it was just as important to us that they not make the off-flavors that wild maltose-negative yeast ordinarily produce. From an evolutionary perspective, the difference in flavor profiles of beers made with wild and domesticated yeast is pretty remarkable. Selection of yeast by brewers had a massive impact in defining our conception of traditional brewing styles, and if you taste beers made with undomesticated yeast, you can quickly appreciate just how adept brewer’s yeast strains have become at making clean beer. To get a better understanding of how our approach compares to undomesticated maltose-negative strains, let’s look back to the sensory data from Maust et al. Two different descriptors stand out.
Figure 5. Production of the off-flavor molecule isovaleric acid by undomesticated yeast and its sensory impact.
First, let's look at how the different strains rated for the “cheese” descriptor. Figure 5 illustrates a spectrum of perceived cheese character across commercial strains. Moderate cheese-like flavor was present in most beers made with undomesticated yeast. Notably, the Berkeley strains exhibit virtually none. (The bottom left panel in Figure 5 shows the orthonasal sensory ratings for beers fermented with 11 different strains from Maust et al., with Berkeley Yeast strains in the left column and other strains in the right.)
Based on the descriptor, and what we know about yeast metabolism, we were pretty sure the cheese character was driven by isovaleric acid. (At the top, Figure 5 how wild yeast’s natural metabolism leads to isovaleric acid.)
You may be familiar with isovaleric acid from Brettanomyces-infected beer, from aged hops, or from sweaty gym socks. (Fun fact: socks get cheesy because the skin microbiome is doing the same chemistry as in wild-fermented beer—it's converting the amino acid leucine, from body sweat, into isovaleric acid.) To firm up our suspicion, we measured isovaleric acid in NA beer made with a Berkeley NA strain and in another commercial NA strain that ranked higher for the cheese descriptor. Sure enough, the levels of isovaleric produced by our strain were well-below the reported flavor threshold, and the other strain produced levels well-above it (Figure 5, bottom right).
Figure 6. Production of the off-flavor molecule 4-VG by undomesticated yeast and its sensory impact.
Second, let’s look at the “spice/clove” descriptor, which is commonly associated with the chemical compound 4-vinyl guaiacol (4-VG). 4-VG production is common for wild yeast, and the strains that make it are referred to as “POF-positive” because of the phenolic off-flavors” they produce. Why do wild strains make this compound? In the left panel, Figure 6 shows the metabolic pathway illustrating how wild yeast produce the phenol 4-VG from phenylacrylic-acid precursors found in plant-cell walls, including barley. The chemistry is directly related to yeast’s ability to detoxify phenylacrylic acids. 4-VG is a by-product of the detoxification process. This trait is useful in the wild world outside the fermentor because undomesticated yeast primarily live on plants.
In contrast to undomesticated yeast, most brewer’s yeast strains have lost the POF trait during the domestication process because 4-VG is an undesirable off-flavor in most beer styles. Many of the strains in Maust, et al. were rated low for the clove/spice descriptor, with one notable exception. (The right panel in Figure 6 shows the orthonasal sensory ratings for beers fermented by the strains from Maust et al., with Berkeley Yeast strains in the left column and other strains in the right.) It’s possible that more than one of these strains are POF-positive, and they were rated low for clove/spice because there was a low phenylacrylic-acid precursor load in the wort prepared in this study. In any event, because the Berkeley strains were developed from a domesticated ale strain, you can rest assured they are POF-negative under all conditions.
Maintaining Process Efficiencies
Beyond the myriad brewer’s yeast traits that affect beer flavor and quality, there are two key traits related to process efficiency: rate of attenuation and flocculation.
Figure 7. Comparing attenuation and ethanol production by NA yeast strains used in Maust et al. Note: Three maltose-positive fermentations were excluded because they greatly exceeded 0.5 percent ABV.
Rate of attenuation is a key trait for NA brewing. In the section above, we described how slow attenuation with undomesticated yeast poses a challenge not just for timely production, but also for preventing contamination by maltose-positive brewer’s yeast. Conversely, a rapid rate of attenuation allows for a shorter fermentation time and prevents a low-level contamination event from becoming a problem. Returning to the data from Maust et al., we see in Figure 7 that the Berkeley strains (green) exhibit a rapid rate of attenuation, reaching terminal gravity and ABV within 12 hours, whereas most of the other strains (gray) in the study attenuate more slowly. The challenge of a longer fermentation time is illustrated in the data in Figure 7, where one of the maltose-negative strains reaches an initial plateau of ~0.3 percent ABV, and then enters a secondary fermentation after 96 hours that drives the beer above 0.5 percent ABV. In a commercial setting, that would create a problem, and a dilution would be required to keep the product in spec. In contrast, Berkeley strains finish within 24 to 48 hours, allowing for cold crash at 48 to 72 hours, limiting the potential for over-attenuation by a competing strain.
Finally, let’s talk about flocculation. This is a fascinating trait from an evolutionary perspective, as flocculation is thought to be an example of the Green-beard effect, a phenomenon in which a single gene can promote altruism toward a group of other individuals that share the trait. In the case of wild yeast, when they encounter a severe environmental stress, such as hydrogen peroxide, many individual cells adhere together to form “flocs,” where the cells in the outer layer insulate the middle cells from the environmental stress. Who knew yeast could be so selfless?
While it is normal for wild yeast to flocculate in highly stressful environments, wild yeast strains don’t tend to flocculate in NA brewing conditions. Over the centuries of domestication, brewer’s yeast has been selected to flocculate at terminal gravity. Similar to the performance of domesticated yeast, the Berkeley strains flocculate once they hit terminal. This is ideal for NA beer production, as the in-fermentor separation results in a brite beer after 48 hours, so it won’t hold up a centrifuge run or clog a filter en route to the packaging line.
Sometimes Science Begets a More Natural Solution
At Berkeley Yeast, we believe that less can be more. The most elegant solutions don’t come from more processing and more chemical engineering, but in refining the biology of the yeast itself. While the approach of rewiring yeast’s metabolism may seem like a break with tradition, in the context of NA beer, it actually adheres more closely.
To the modern drinker, a beer made with maltose-negative fermentation feels more natural than one processed through mechanical dealcoholization and added flavors. Similarly, fermentation with the Berkeley strains feels more traditional than using an undomesticated yeast strain that makes untraditional flavors. Beer fermentation is the world’s oldest biotechnology; by further refining the genetics of a traditional brewer’s yeast—much like brewers have done via selection for centuries—we’re simply updating that technology. Now you can make NA beer that tastes more like beer, using the same process you’ve always used.
For more information, additional resources, or to purchase Berkeley’s strains, visit BerkeleyYeast.com.