One of the most rapidly growing types of alcohol being consumed is low alcohol beer (LAB), also known as light beer, or near-beer. My local booze store has whole shelves dedicated to LABs (above), and their number is growing (global LAB consumption doubled between 2018 and 2024). LAB has the advantages of fewer calories and, particularly important after the recent worries about the toxic effects of alcohol (cancer risk goes up at any level of consumption!), less alcohol. Not to mention, you can have several beers and still drive home safely .

To be classified as a LABs in the USA, it must have less than 0.5% alcohol, as compared to 5% or more for regular beer (different countries have different limits). The number 0.5% arose during Prohibition, when Congress passed the Volstead Act, which set that as the permissable level for alcoholic beverages.

Beer 101

Beer is one of those foods, like sourdough bread, that contain very few ingredients, but is tricky to make. Only grains, hops (a plant product that adds bitterness and other flavours), water, and yeast. Yeast is the key, but all of the conditions for making beer (and sourdough, as I’ve learned) influence the quality and taste of the product. The time, the temperature, the treatment of the barley used to make the beer, and, most importantly, the type of yeast.

The process of making beer, in contrast to its list of ingredients, is complex. The barley grain is first soaked in water to initiate germination. A little plant starts growing from the barley seed, and enzymes are activated that break down the cell walls, the starches, and the proteins in the barley seed. The product of this step is called malt, which is dried and ground up and mixed with hot water in preparation for the next step, mashing.

Mashing fully releases the starches from the barley, producing some simple sugars and some larger carbohydrate polymers, including lots of maltose and maltotriose. Maltose consists of two chemically-linked glucose molecules, maltotriose, three. These maltose sugars make up over 60% of the carbohydrate of the mash product, which is called wort. The wort also contains protein, which will make an important contribution to the flavour of the beer. After a couple of clean-up steps, the wort is ready for fermentation.

Yeast is added to start fermentation. The strain of yeast determines the kind of beer produced, and there isn’t enough room on this website to describe all the possible variations: ales, lagers, stout, porter . . . . What all beer-producing yeasts have in common (and this is also true of bread-making yeast) is that they use the sugar glucose and produce ethanol (alcohol) and carbon dioxide.

A soupçon of metabolism

Yeast that produce beer use an evolutionarily ancient form of anaerobic (oxygen-independent) energy metabolism, one that takes place in bacteria, yeast, plants (at night), mice, and humans. It’s called glycolysis (from glyco-, sweet, and -lysis, to split). In the hard-working, oxygen-starved muscle cells of the human sprinter, glucose is broken down to lactic acid by glycolysis. In fermenting yeast, growing anaerobically, the product of glycolysis is ethyl alcohol.

(If oxygen is present, the yeast convert all of the sugar to carbon dioxide and water, plus energy, and you end up with a fizzy, flavoured drink containing no alcohol. In the oxygenated human muscle, think marathon runner rather than sprinter, the glucose is also oxidized to carbon dioxide and water. These aerobic (oxygen-dependent) pathways  are also, like glycolysis, almost identical in yeast and humans.)

That’s the elevator version of how yeast produce alcohol. But there’s a whole other stream of metabolism going on at the same time, and without that, we’d have just alcohol, not beer. That other stream consists of numerous pathways that convert other barley breakdown products, particularly the amino acids released by protein breakdown during malting and mashing. These amino acids are converted to flavour components that make our favourite brew our favourite. They include molecules such as higher alcohols (bigger than ethanol), esters (which are combinations of alcohols and organic acids), and aldehydes and ketones (modified versions of higher alcohols). They are characteristic of the strain of yeast, and their presence and levels are modified by everything else going on – the heating of the mash, the length and severity of the malting, the temperature of the fermentation. . . In short, the brewer’s secret recipe.

So how do you produce a low-alcohol beer, of any kind?

Low Alcohol Beers, and how to make them

There are several pathways to getting Low Alcohol Beers, LABs. You could simply ferment less, stop the fermentation earlier, before the alcohol level rises. But that also limits the development of flavour, and results in a pretty uninteresting beer (although it is sometimes done). The usual processes for producing LABs, of which there are two types, are either to remove the alcohol post-fermentation, or to use genetics to meet the challenge.

There are also two methods for removing alcohol from beer that has completed fermentation. The first is to distill it off. Alcohol has a lower boiling point than water and most of the flavour molecules produced during fermentation, so distillation selectively removes ethanol. The distillation can be carried out at reduced pressure, thereby lowering the boiling point of ethanol even more, and not affecting flavour molecules by heat. However, some of the flavour components are also going to go up in steam, so this method has its limits.

The most popular commercial method for reducing the alcohol content of finished beer is to put the liquid in a special membrane and subject it to pressure. Such membrane technology, called ‘reverse osmosis’, is used for water purification. In the production of low-alcohol beer, it allows water and ethanol to pass through, but holds back the flavour molecules, which are larger. The osmosis can be stopped at the right level of alcohol hold-back, and water added back to produce a low-alcohol, fairly tasty beer. But it, too, is limited by potential loss of flavour components.

The third way

The most interesting and appealing method of producing LABs is based on biology, and calls on yeast genetics to do the heavy lifting. The beauty of this approach is that genetics is very good at providing biological variation (it’s why evolution works). In the case of Low Alcohol Beer, strains of yeast have been generated that have an attenuated ability to use barley sugars (attenuated is an actual term in beer brewing; it refers to the amount of the sugars that are converted to ethanol and carbon dioxide during fermentation.)

An important version of the LAB-producing yeast has lost the enzyme activity that breaks down the maltose and maltotriose carbohydrates to glucose. Since glucose is the only sugar that can enter glycolysis, this limits the rate of alcohol produced by the yeast. These yeast can only use about 25% of the carbohydrate derived form the original barley. But the flavour pathways are intact, and so you produce that holy grail: low alcohol, flavourful beer.

Created by Admin, with help from Dr. Google, ChatGTP, and my old Biochemistry textbook.

Reference material

Basic Fermentation

More Basic Fermentation

Low Alcohol Beer for the Home Brewer