Tastes Great, Less Filling? Crafting low-carb beers

The keys to clearly understanding this topic are knowing about the types of starch present in a brewery mash and how malt enzymes act upon these large carbohydrates, appreciating how exogenous enzymes can be used to step beyond the boundaries of malt enzymes alone, and considering alternative ingredients that leave little to no residual carbohydrates in beer after fermentation. Sounds like you have been pretty successful in your brews. I am going to provide a bit of a background for readers who may not be as advanced in their pursuits of low-carb beers as you are, so bear with me for a bit.

There are generally two sources of fermentables sugars available to beer brewers: 1) Starch-derived sugars from cereal grains and 2) simple sugars, such as sucrose (cane and beet sugar), fructose (fruit sugar), and glucose/dextrose (corn sugar). Simple sugars can be completely fermented by yeast to yield ethanol and carbon dioxide, although complete fermentation is rarely a reality and some sugar is usually present following beer fermentation, but the mixture of carbohydrates produced from cereal grains in a brewer’s mash contains fermentable and unfermentable carbohydrates. It’s the unfermentable sugars that contribute to carbohydrate calories in beer.

The two types of starch found in cereal grains are amylose and amylopectin. Amylose is a straight-chain carbohydrate and amylopectin is a branched molecule. Amylose is almost entirely converted into fermentable sugars (glucose, maltose, and maltotriose) by beta amylase during mashing. Amylopectin is converted, through the joint actions of beta amylase (Pac Man enzyme that starts at a free end of amylose or amylopectin and produces maltose with each chop) and alpha amylase (random chopper that whacks up starch into smaller chunks by cleaving bonds within the starch molecule), into a mixture of fermentable sugars and left over bits called beta-limit dextrins. The takeaway point is that all cereal starches in a brewery mash contain beta-limit dextrins because neither beta- nor alpha-amylase can cleave the branch points in amylopectin. Beta-limit dextrins can be metabolized in our bodies and represent the majority of carbohydrates in beer.

The two types of starch found in cereal grains are amylose and amylopectin.

Low-carbohydrate beers can be made through several routes. One way to reduce the carb and alcohol concentration of beer is to dilute with water, but the end result is simply watery beer and not what you seek. Another approach is to substitute cereal starch, and the hydrolytic products that follow mashing, with simple sugars such as sucrose, dextrose, and/or fructose. I personally like this method for home use because it comes with minimal risk of disappointment while being simple and predictable. But for brewers really seeking the ultimate in low-carb brewing, you need to look outside of the malt kernel for an enzyme capable of breaking alpha 1-6 bonds. The stalwart tool favored by commercial breweries is amyloglucosidase (AMG), sometimes called alpha-glucosidase. AMG is secreted by fungal Aspergillus species and commercial suppliers sell purified preparations, such as White Labs Ultra-Ferm, to brewers and to companies that produce liquid brewing adjuncts.

Although Miller Lite was the first nationally available light beer, the history of the style began with Dr. Joseph Owades’ work with Gablinger’s Diet Beer at Rheingold Breweries (Brooklyn, New York in 1967). In spite of being a commercial flop, Owades passed on the science behind the formulation to the Peter Hand Brewery in Chicago, famous for their Meister Bräu brand. Meister Bräu Lite was a success in the local Chicago market, but the brewery declared bankruptcy and Miller Brewing purchased its brands, including Meister Bräu Lite, in 1972. With some recipe tweaks to increase beeriness, Miller Lite was born and the rest is history.

Plotting information about carbohydrates, calories, and alcohol from light beers, regular beers, seltzers, and Bridge’s Prime Time you cite in your question provides insights into these beverages. The data shown in Table 1 above was collected from information posted by these breweries on their websites and graphically displayed using a bubble plot to help show clusters within the selection of beers.

The beers making up Cluster A in the bubble plot are Budweiser, Molson Canadian, Coors Banquet, Miller High Life, and Sierraveza. All of these beers, except for the all-malt Sierraveza, are brewed from malted barley and rice or liquid adjunct. And all beers in Cluster A have similar carbohydrate, % ABV, and caloric contents. It’s important to note that liquid adjuncts have varying compositions and fermentabilities that are tailored for different applications. The types of liquid adjuncts used for full-strength lagers often mimic the fermentability of “normal” wort and explains how the adjunct-containing beers in Cluster A are similar to the all-malt Sierraveza.

Cluster B includes Miller Lite, Coors Light, and Bud Light; the beers come to mind when American beer drinkers think of light beer. These beers have 84% of the alcohol, about 75% of the calories, and between 26–62% of the carbohydrates as their full-strength siblings. The low carbohydrate level of these beers is achieved using a combination of brewing technique, ingredient selection, and the use of exogenous enzymes from fungal sources. I would say your homebrewed light beer, with 3.3 grams of carbs and 3.7% ABV, falls nicely into the light-beer category represented by Cluster B on our graph. Molson 67 falls outside of any cluster, labeled “Outlier” on the bubble plot, and is made by producing a light beer similar to Miller Lite but with more dilution with water following the fermentation.
Bridge Prime Time and White Claw hard seltzer make up Cluster C. These products have the alcoholic strength of the beers in Cluster A, the same caloric content as Bud Light, and fewer carbs than any of the beers in Clusters A and B. It’s easy to explain why a seltzer would fall outside of beer clusters, but seeing where Prime Time falls in the bubble plot space is a surprise because it is beer, not a seltzer. And it is clearly different from other light beers in that it has lower carbs, more alcohol, and the same calorie-count as Bud Light.

According to the Prime Time label, it contains water, barley, flaked corn, hops, and yeast. Based on the carb count and % ABV, I expected to see sucrose in the ingredient mix. The word “malt” does appear on other Bridge Brewing labels so it’s reasonable to conclude that Prime Time does not contain malted barley and that all of the starch conversion was accomplished using exogenous enzymes. Enzymes were definitely added to the mash and it’s likely that AMG was added to the fermenter where it has the longest time to break down dextrins into fermentable sugars. Prime Time is also hopped with Citra® and El Dorado® and that probably is the main differentiator in its flavor profile. Based on what I can see on the Bridge website, some sort of colored ingredient is also used and this may bring with it some added flavor without bringing carbs.
You asked how low-carb beers are brewed and the answer thus far generally addresses your question. Here are a few thoughts about brewing these types of beer at home:

• Low-carb, low-alcohol, and low-cal beers usually have a thin mouthfeel and a generally “watered-down” sensory profile because the numerical targets require the reduction of the compounds that add to the fullness of beer. Homebrewers may want to liven the party with hop flavor, a kiss of specialty malt, and even aromatic fruit flavors.
• The easiest way to brew low-carb, light beers at home is by adding simple sugars to normal wort and shooting for a lower original gravity.
• If you want to brew a beer like Prime Time, consider simple sugars and AMG added to the fermenter.
• Hop bitterness is amplified in lighter beers. Borrowing hopping techniques from hazy IPAs is something to consider with very low bittering hops added.
• The important thing to consider when consuming foods of all types is the total amount of food compounds consumed, not the concentration of the compounds of interest. One way to consume fewer carbs from beer is to simply consume less beer.

When I look at the numbers from Molson 67, I cannot help but ponder two competing thoughts: 1) Molson 67 looks like the sort of beer that is consumed by the liter, and 2) it would be more cost effective to pour two bottles of Miller Lite in a liter mug and top up with water than buying three bottles of Molson 67. Oops! Did I just write that?

Response by Ashton Lewis.