GC Reveals How Yeasts Spoil Non-alcoholic Beer

Alcohol-free and low-alcohol drinks are big business, and the market for them is growing fast. Because they contain little or no alcohol, they offer different conditions from regular beer, which makes them more likely to spoil. One major threat in brewing comes from yeasts that can spoil beer, usually by changing how it tastes and smells. However, little is known about how these yeasts affect alcohol-free and low-alcohol drinks.

To fill this gap, researchers set out to learn how beer-spoiling yeasts change the flavor of non-alcoholic beer. They tested 30 different strains of these yeasts to see how much spoilage each one caused. Using atmospheric-pressure chemical ionization–mass spectrometry (APCI–MS), they identified the strains that had the biggest effect on the beer's aroma. They then took a closer look at those strains using two other methods. Headspace–gas chromatography with flame ionization detection (HS–GC–FID) measured whether the yeasts changed the levels of aroma compounds normally found in beer, and gas chromatography–mass spectrometry (GC–MS) searched for unusual aroma compounds that would not normally be there. A paper based on this research was published in the International Journal of Food Microbiology.¹

What Are NoLo Beers, and Why Are They More Likely to Spoil?

Alcohol-free and low-alcohol beers, often called "NoLo" beers, are one of the fastest-growing parts of the global market for fermented drinks. This growth is driven by drinkers who want to cut back on alcohol but still enjoy the taste and feel of regular beer.² Brewers can make these beers in two main ways: by physically removing the alcohol, or by using biological methods. The physical approaches include heating the beer or passing it through special filters to take the alcohol out of regular beer.³

Regular beer has several built-in defenses that keep germs from growing. These include bitter compounds from hops, a fairly acidic taste, few nutrients for microbes to feed on, very little oxygen, plenty of carbon dioxide, and, of course, alcohol, typically around 4% to 8%.^4,5 In alcohol-free and low-alcohol beers, however, there's little or no alcohol, often more leftover sugar, and other changes to the drink's makeup, all of which can make it easier for microbes to survive.² The authors of the paper point to several studies showing that these beers are more prone to spoiling, sometimes even by microbes that don't usually cause problems in regular beer.¹

How Did Beer-spoiling Yeasts Affect the Flavor and Alcohol Content of Non-alcoholic Beer?

From the initial screening of 30 beer-spoiling yeast strains, 14 strains representing key beer-spoiling yeast species were selected, including Brettanomyces, Candida, Debaryomyces, Hanseniaspora, Kazachstania, Kluyveromyces, Pichia, Saccharomyces, Torulaspora, Wickerhamiella, Cyberlindnera and Zygosaccharomyces.¹

All the beer-spoiling yeasts tended to strengthen the aromas in non-alcoholic beer, which threw its flavor out of balance. Brettanomyces yeasts caused the most spoilage, producing unpleasant-smelling compounds, including ones with smoky, spicy, cheesy, or sweaty notes. Strains of another yeast, Cyberlindnera saturnus, produced high levels of fruity-smelling compounds, along with acrolein, a chemical that may cause cancer.¹

Spoilage also created another problem: alcohol. Brettanomyces, Saccharomyces, and Zygosaccharomyces yeasts were especially good at producing much higher alcohol levels in non-alcoholic beer. This kind of unplanned second fermentation is a serious concern for alcohol-free and low-alcohol beers, because the extra alcohol could mean the beer no longer counts as non-alcoholic. Since brewers are legally required to label their products accurately, unexpected alcohol could lead to legal trouble and harm a brand's reputation.¹

“The data,” write the authors of the paper,¹ “provides insight into the relative spoilage potential of beer-spoiling yeasts in relation to standard beer styles, indicating that the negative effects of contamination are exacerbated in non-alcoholic beer. Importantly, elevated alcohol production was also observed, with both commercial and legislative implications. This data is directly relevant for the global brewing industry, and other related sectors where the demand for no- and low-alcohol alternatives is prevalent.”

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References

1. Roselli, G. E.; Smart, K. A.; Crow, M. et al. The Impact of Beer-spoiling Yeast on Flavour Development in Non-alcoholic Beers. Int J Food Microbiol. 2026, 463, 112099. DOI: 10.1016/j.ijfoodmicro.2026.112099
2. Roselli, G. E.; Kerruish, D. W. M.; Crow, M. et al. The Two Faces of Microorganisms in Traditional Brewing and the Implications for No- and Low-alcohol Beers. Front Microbiol. 2024, 15, 1346724. DOI: 10.3389/fmicb.2024.1346724.
3. Brányik, T.; Silva, D. P.; Baszczyňski, M. et al. A Review of Methods of Low Alcohol and Alcohol-free Beer Production. J. Food Eng.2012, 108, 493-506. DOI:10.1016/j.jfoodeng.2011.09.020
4. Leistner, L. Basic Aspects of Food Preservation by Hurdle Technology. Int. J. Food Microbiol. 2000, 55, 181-186. DOI: 10.1016/S0168-1605(00)00161-6
5. Menz, G.; Aldred, P.; Vriesekoop, F.; Pathogens in Beer in Beer in Health and Disease Prevention; V. R. Preedy (Ed.). Academic Press, 2009, pp. 403-413