This week I continue my series on brewing low alcohol and non alcoholic beers. I’ll cover new low-alcohol yeasts, arrested fermentation and also provide tips on finishing and packaging your low alcohol beer. In Part 1, I covered basic methods and achieving proper beer balance. In part 2, I wrote about boil off, distillation and low fermentability wort methods. Today I’m going to cover low alcohol yeasts, arrested fermentation and carbonation and long term beer stability.
Low Alcohol Yeasts
One of the most promising new developments in low alcohol beer brewing is the availability of low alcohol yeasts. These special yeasts are bred or engineered to ferment a beer while producing very low levels of alcohol. I’ve sampled some commercial examples of these beers and they are surprisingly good if you can achieve the right malt/hop/body balance when formulating your recipe.
The key with this method is using “maltotriose negative” yeasts that will easy ferment simple sugars like glucose, fructose and maltose, but these strains have a very limited ability to ferment longer sugar strains like maltotriose and dextrins. This results in much lower levels of alcohol produced in the final beer. Some strians are also maltose-negative, meaning they won’t ferment maltose either. A yeast that is both maltose and maltotriose negative will only ferment simple sugars like glucuse, and will produce the lowest levels of alcohol.
I should also note that often these low alcohol yeasts are combined with the low fermentability wort methods covered in part 2, including using a high temperature mash, and relatively low starting gravity with a matched hop rate to achieve good beer balance and body. A high mash temperature, for instance, will produce more unfermentable sugars and maltotriose which will not ferment with a low alcohol yeast.
Maltotriose and Maltose negative yeasts are a relatively new offering for many yeast labs. Many of these are non-Saccromyces strains, and some are GMO though there are quite a few non-GMO strains available. There are also some challenges with producing these strains commercially as they don’t ferment many common sugars so production yields are lower. As a result they can be more expensive than conventional yeast strains.
Most of these yeast strains produce low levels of 12-15% attenuation, and some require pH adjustment of the wort for best results. Using proper techniques, it is possible to ferment a beer in the 1-2% ABV range or lower using these strains. Care must also be taken with finish and packaging as some strains are prone to further fermentation in the bottle.
Some of the strains available to homebrewers include:
- WLP618 Saccharomycodes Ludwiggi (White Labs) – A neutral strain with some ethyl acetate production, but low maltose and maltotriose consumption.
- WLP603 Torulaspora Delbrueckii (White Labs) – Will not ferment maltose of maltotriose. Fruity, high ester profile suitable for Belgians, Saisons and fruity IPAs.
- WLP686 Zygosaccharomyces Lentus (White Labs) – A neutral strain with partial inability to ferment maltose. However difficult to grow/reproduce.
- SafBrew LA-01 (Fermentis) – A Saccharomyces cerevisiae var. chevalieri variant, this yeast does not ferment maltose or maltotriose. A fairly subtle, neutral aromatic profile for low alcohol beers.
- LalBrew LoNa Hybrid Yeast (Lallemand) – A maltose-negative and maltotriose negative hybrid yeast. A clean fermenting ale yeast with a neutral flavor, no phenolics or aldehydes. They recommend pasteurization of the finished beer for stability.
- SmartBev NEER (CHR-Hansen) – A maltose and maltotriose negative yeast that only metabolizes monasaccharides. Lowers malt profile, and yields a neutral malt profile with good mouthfeel. Produces very low alcohol levels. They recommend using oxygen dosing at start of fermentation. Also you may find my interview with Simon Carlsen from CHR Hanson interesting here.
- WSL-17 Saccharomycodes Ludwigii (Hefebank Weihenstephan) – Another maltose and maltotriose negative strain for lor alcohol beer production.
The list above is in no way comprehensive, as major yeast labs are adding new low alcohol strains all the time. I personally believe that using low alcohol yeast strains along with techniques like higher mash temperatures is probably the easiest way to produce consistent low alcohol beer at home.
Arrested Fermentation
The idea behind arrested fermentation is to halt the fermentation when the beer reaches a target alcohol level. At the commercial level, brewers can flash pasteurize a beer to kill of the yeast. You can achieve a similar result by rapidly raising your fermenting beer to 140F (60 C) for about 15 minutes, but in practice this can be difficult for the homebrewer to achieve without transferring the beer to smaller vessels. Ideally you want to transition the temperature very quickly and maintain the elevated temperature for only a short period to pasteurize without adversely affecting the flavor of the beer.
You can also chill beer to near freezing which will deactivate the yeast, and then filter the yeast out using an appropriate filter. This is a practical solution for home brewers who have access to refrigeration and suitable filters.
Finally you can use Potassium Sorbate (sorbate) and potassium metabisulfite (sulfite) to inhibit fermentation. This is widely done in mead and cider production before backsweetening to prevent further fermentation. The problem with this approach is that the sorbate/sulfite combination only prevents further growth and reproduction of the yeast cells and it does not actually halt ongoing fermentation. So fermentation can continue even after the sorbate/sulfites are added. However the sorbate/sulfite combination is an effective preservative if you want to prevent a secondary fermentation after packaging and it provides some level of oxygen protection as well.
Reverse Osmosis, Centrifuge Separation
These techniques are used at the commercial level to halt fermentation and separate the yeast from the beer which prevents further fermentation. Except for the cold filtering method (mentioned above under Arrested Fermentation), most of these techniques are not really practical at the homebrew level. Most homebrewers don’t have a centrifuge or osmosis system designed to separate alcohol in their basement.
Carbonating, Packaging and the Stability of Low Alcohol Beer
Low alcohol beers present additional challenges when we age, package and store them. Because of the very low alcohol levels and lower hop levels needed to achieve beer balance, these beers are prone to both the restart of fermentation and also infection. Alcohol and hops are key preservatives, so lower levels of both present risks. Also there is the challenge of carbonation, which typically cannot be done naturally with sugar/yeast without risking a restart of fermentation.
To solve the carbonation problem, you are largely restricted to forced carbonation using a keg and CO2. You can later bottle the beer from the keg using something like a beer gun, but it is very difficult to naturally carbonate and bottle these beers without the risk of either a flat beer or bottle bomb.
To reduce the risk of infection and the restart of fermentation, commercial beers use a combination of filtering, pasteurization and preservatives. At the homebrew level, you can purchase suitable filters to remove the yeast by transferring your beer from one keg to another through the filter. You can also pasteurize beer as mentioned above by rapidly heating it to approximately 140 F (60 C) for 10-15 minutes and then rapidly cooling it back down to minimize time exposed. This can be done after bottling, as the smaller bottles transfer the heat better.
For preservatives, the above mentioned potassium sorbate and potassium metabisulfate combination is effective at inhibiting further yeast growth and also the sulfites provide some antibiotic and antioxidant protection. Some brewers mention this can alter the flavor slightly, but not necessarily in a negative way. There is a sulfite/sorbate calculator for this purpose in BeerSmith.
Finally I will mention it is best to store these beers cold if you have the capability. Heating your beer ages them rapidly, and since these beers are more susceptible to infection, oxygen and aging it is best to keep them cold to maximize shelf life.
Conclusion
Even though this was a three part series, there is still quite a bit more that could be written about low alcohol beers and brewing. In addition to the technical details of the methods above, and the topic of beer balance I touched on in part 1, you can research further topics like controlling pH for these beers, the wide use of whirlpool and dry hopping to create aromatics and much more. However, I hope you enjoyed this three part overview on low alcohol beers.
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