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Low-Alcohol Beer Production, Gravity Drops and the Effects of a Cold-Water Extraction

Q I have been seeing more Non-Alcohol and low-alcohol beers on the shelves along with a great selection of the styles being brewed. How are brewers making these beers and are there any new methods homebrewers may want to give a try?

Nick Arnold
Dry Creek, Arizona

A Before jumping into a review of some of the methods used to produce no- and low-alcohol beers, so-called NABLABs where NABs (non-alcohol beers) contain less than 0.5% ABV and LABs (low-alcohol beers) contain greater than 0.5% ABV, I want to provide a sort of spoiler alert; there are not a bunch of great methods for homebrewing NABLABs. However, because of the creativity of homebrewers, folks will likely come up with some great ways in the near future by riffing on newer commercial techniques to fill this void.

Alcohol Removal

One common strategy used for decades in the production of NABLABs is removing alcohol from relatively normal beers. Because some aromas are lost in the process and the flavor balance of the beer changes, beers intended for alcohol removal are brewed with the end-goal in mind, hence the “relatively normal” description. The two most common ways to remove alcohol from beer are vacuum distillation and reverse osmosis (RO).

Most beer drinkers who have consumed a variety of NABLABs have probably come across beers with a cooked or burnt flavor. The early distillation methods used to produce NABLABs worked for alcohol removal, but many of these systems were a bit rough around the edges and made for some interesting flavors. Beer distillation is much more advanced these days and current hardware combines low-temperature, vacuum distillation with aroma recovery to produce some really nice tasting beers.

Beer distillation is much more advanced these days and current hardware combines low-temperature, vacuum distillation with aroma recovery to produce some really nice tasting beers.

These systems feature a tall column filled with a cleanable packing material, a beer inlet and outlet circuit, and a gas stripping circuit. In simple terms, beer is pumped into the top of the column and allowed to flow down through the packing while an inert stripping gas is introduced into the bottom of the column and removed from the top along with the alcohol. The beer temperature in these systems is about 110 °F (43 °C) at 100 mbar (10% of atmospheric pressure). If you have sampled a wide selection of NABLABs from the market, chances are high that you have tasted brews made using this method.

Many brewers know about reverse osmosis water treatment, where nearly pure water flows across a membrane, leaving a concentrated retentate stream on the supply-side of the membrane and allowing for the removal of this concentrated water stream in the reject stream. The same basic technology can be used to remove alcohol and water from beer to produce NABLABs. When RO is used to dealcoholize beer, water is added back to balance the water removed with alcohol.

Arrested Fermentation

Some brewers figured a great way to make NABLABs is to greatly minimize ethanol production using various arrested fermentation strategies. Some of these beers are taken through an alcohol removal process, but are different from the “brew normal beer and remove the alcohol” strategy because of the very low alcohol levels produced by the method. One drawback to arrested fermentation is a worty note often associated with these beers. In my opinion, that critique is not a show-stopper because today’s beer consumer has developed a more diverse palate and beer produced from arrested fermentation could easily be spiffed up by adding acids and flavors to make for some interesting interpretations of trending beer styles.

This is one method that could be performed at home because the principle is pretty simple; stop fermentation by rapidly chilling beer before much alcohol is produced, remove the yeast by centrifugation (not at home, of course) and/or filtration, and stabilize the product by pasteurization. The last step could be replaced by using a combination of sorbate and sulfite or the beer could be kept very cold in a keg and carefully monitored by frequent drinking to spot signs of any re-fermentation. If this method is used, do not attempt skipping the filtration step, keep all parts of the dispense system in the cooler, and DO NOT bottle these beers. A cobra-head faucet is the best choice here. And make sure the beer pH is below 4.6 to prevent the growth of Clostridium botulinum spores.

Maltose-Negative Yeast Strains

Some yeast strains are able to ferment glucose, but not maltose or maltotriose. These yeasts are known as maltose-negative strains and offer a relatively simple way of producing low-alcohol beers. Like beers produced using the arrested fermentation method, these brews contain fermentable sugars, and also are likely to require pH adjustment to bring beer pH below 4.6. The yeast companies selling maltose-negative yeast strains advise brewers to pasteurize these beers after packaging.

Figure 1

Homebrewers are going to do what homebrewers do and give these strains a try by hitting up commercial brewers for yeast. Just keep your eyes open and DO NOT bottle beer containing fermentable sugars.

Let’s take a break from the process and dig a bit deeper into the carbohydrate profile of wort. It goes without saying that there are multiple factors influencing carbohydrate profile, but we can look at values for typical wort produced with-out special malts or adjuncts using the standardized congress mash method. We can see from Figure 1 that typical wort contains about 15% glucose.

One technique that can be employed to produce low-alcohol beers is using a yeast strain that is incapable of fermenting maltose or maltotriose. Photo courtesy of Fermentis

When maltose-negative yeast strains like Saccharomyces cerevisiae var. chevalieri are pitched into 12 °P (1.048 SG) wort, the maximum glucose they can consume is about 19 grams of glucose per liter of wort (1 liter x 0.12 kg extract/kg wort x 1.048 kg wort/liter x 0.15 kg glucose/kg wort x 1,000 grams/kg). When glucose is fermented, it is converted to ethanol (51% by weight) and carbon dioxide (49% by weight). In other words, maltose-negative yeast produce beer with about 1% ABV when the wort OG is 12 °P (1.048 SG). If the goal is beer with < 0.5% ABV, simply lowering the OG to 6 °P (1.036 SG) does the trick.

So, there you have it, Nick. Those are some of the most common methods to remove alcohol from beer. I am neither advocating nor opposing any of these methods for consideration at home. Just trying to answer your question in basic terms. But . . . if someone wants to play around with any of these commercial methods and report back about the results, we certainly would love to hear about the trials!

And, for the record, be sure to measure the pH of any homebrewed NABLABs and adjust the pH below 4.6 if required. This is a critical pH in the world of food processing and distinguishes high-acid foods (pH<4.6) from low-acid food (pH>4.6). The other very important safety reminder is packaging; DO NOT bottle or can beers that contain fermentable sugars unless the beers are pasteurized in the package.

Q I’ve been brewing for 7 years and have noticed a strange trend that no one has been able to explain to me. I always see a pretty significant drop in gravity between ending my boil and transferring the cooled beer into the primary. For instance in the last beer I made, I checked the gravity using a refractometer (sample cooled to approximately 70 °F/21 °C) about 5 minutes before flame out and it was 1.104 (making a big Belgian Strong). I cooled with a copper coil and when I sampled the beer going into the fermenter my gravity had dropped to 1.088! This happens to me every time. I typically use fining agents.Do I have sugars dropping out during cold break?

Mark Mathews
Lapeer, Michigan

A I want to begin with a true confession about how I write this column. Using no special system, I select questions for discussion from those that are sent into BYO. The best questions are those with enough wiggle room to find some fun rabbit holes and angles. And most of the questions I select are answerable! I selected your question because it sparks my interest and have been sitting on this for a while hoping to come up with something really clever. But I haven’t, and, in the process, I let your question get a bit long in the tooth before answering. Sorry for the delay! I will give you what I have.

For starters, I have never experienced gravity drops between kettle samples and fermenter samples. But have observed exactly the opposite, where the gravity goes up from kettle to fermenter, both in 5-gallon (19-L) and 500-gallon (19 hL) brew kettles. As crazy as it may sound, wort can stratify in brew kettles for a number of reasons, including how kettles are filled during wort collection, how solid and liquid sugars are sometimes added to the kettle towards the end of boiling, and how top-up water is sometimes added towards the end of the boil. All of these practices may result in heavier wort on the bottom of the kettle compared to the top of the kettle. Hmm, by simply writing this paragraph, I think I may have a plausible suggestion to explain why your observations are the opposite of mine. And without further ado, let’s get into what may be happening.

Until about five minutes ago, the only explanation that made sense to me was a leak in your wort cooler that you never noticed. Most homebrewers don’t run cooling water through an immersion chiller when not in use, making pinhole leaks difficult to spot. Another possibility is that you have a leaky connection on the water supply and are leaking water into the kettle from the connection. The latter is much less likely than the pinhole idea.

Although this general idea may sound a bit far-fetched, leaks in heat exchangers are a real concern for food and beverage producers because these tools can and do develop leaks. Flash pasteurizers used in the dairy industry are designed to ensure that pasteurized milk flows into the raw milk side of the heat regeneration section of the flash pasteurizer in the event of a leak. And differential pressure is monitored to make sure the raw pressure is never higher than the pasteurized pressure. My gut feeling, however, is that this is not your problem.

Your problem is probably related to your sampling method. Many brewers grab wort samples from the brew kettle using some sort of sampling device. Indeed, there are plenty of action shots of brewers grabbing wort samples from copper kettles with fancy looking tools because this part of the brewing process is important to all brewers. If wort gravity is not homogenous, this method usually pulls a lower gravity sample because the heavy stuff sinks. In your case, I am betting that you pull your sample from your kettle’s outlet valve. And by doing so, your sample may be different than wort at the top of the kettle, thus explaining your issue. Next time you brew, drain some wort into a clean pot, pour the wort into the top of the kettle, and repeat a few times. If this solves your issue, let us know!

Q I’ve been contemplating brewing a table beer and was reading up on BYO.com about it. I was wondering if after a cold-steep mash can those grains be mashed at typical saccharification rest for use in a second beer or does the cold-steep rob the grain’s enzymes? Would a decoction mash of those grains be useful if the diastatic power is now lower?

Royce Faina
Philadelphia, Pennsylvania

A Homebrewers are always pushing the envelope for cool ideas and this one is certainly doable. Let’s start with a quick review of what happens in a cold mash. When milled grains, be they unmalted or malted, are mixed with ambient water, soluble carbohydrates, proteins, and enzymes are brought into solution. Although malt certificates of analyses (COAs) outside of the U.K. don’t report cold water extract (CWE), this value is a handy index of modification. As malt modification increases, so does the solubility of extract in ambient water. The majority of CWE is carbohydrate, but soluble protein is also part of the equation.

In a typical hot mash, the extractables represented by CWE are almost immediately brought into solution, followed by gelatinized starch, then by fermentable sugars and dextrins that come from amylolytic activity during the mash. So-called cold mashes are relatively new to brewing and can be conducted over a range of temperatures and times. The commonality among these mashes is that very little amylase activity occurs; what is extracted is color and flavor, especially from specialty malts.

Because CWE values from paler malts are typically around 20%, compared to about 80% for hot water extract (HWE) values, there is a lot of stuff remaining in malt following cold-steep extraction. Specialty malts have a wider range of CWE values, but the values are rarely reported because specialty malt COAs are usually limited to color, HWE, and moisture.

Assuming that the cold-steep method is being used to extract rich malt flavors to present a different flavor-profile in the finished beer, using hot sparge water or mashing the drained grains into a hot mash would defeat the purpose of the cold mash. One strategy to maximize the goods in the cold steep would be draining the wort for use in a cold-steeped beer, and then using the “spent grains” as a component for a second brew. Yes, enzymes are extracted in the cold-steep method, but if the spent grains are used as a component in the grist bill for a second brew you don’t need to worry much about enzymes because more malt will be added. You could use infusion, step, or decoction mashing methods for the second brew, but if you are not using undermodified malt in the cold-steep mash, an infusion mash will work well for the majority of modern malts.

Issue: September 2022
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