Low Carbohydrate Craft Beer

Low Carb Beer Information

With the increased popularity of low-carb diets, we’ve been getting many inquiries regarding low-carb beer-making. So we’ve taken a stab at putting together some of the pertinent facts brewers of low-carb beers ought to keep in mind. Here’s just about all we know…

According to opinion research published by Ipsos Public Affairs on the web, over one-half of American adults believe that the carbohydrate count in vodka is “high” or “medium” and 55% believe this about tequila, even though neither vodka nor tequila contains any carbohydrates, nor does gin, rum or whiskey. The survey also found over two-thirds of adults falsely believing that fruit juice and regular soda are lower in carbohydrates than distilled spirits.

The dieter must understand that carbs are not the same as calories. Starches and sugars are carbohydrates, alcohol is not, but all three contain calories. Therefore, making a low-gravity brew does not necessarily give you a low-carb beer. The carb count in your beer is more determined by process variables than by gravities. To understand why, we must first understand carbs: Carbs are essentially grain starches. In the mash tun, any starch absorbs increasing amounts of water (hydrates) and gradually expands as the ambient temperature increases from cold to warm to hot. Between 158 and 176°F (70 and 80°C) barley starch forms a viscous paste as it gelatinizes. This is important, because starches are more susceptible to enzymatic conversion after they have gelatinized. Starches thin out above 176°F (80°C), at which point they can leach unconverted into the wort, eventually causing a chill haze in the finished beer and contribute to the beer’s carb content. That’s why you should never let the mash temperature rise above 176°F (80°C)!

Barley has about 60 to 65% starch by weight. Before these complex carbohydrates can be metabolized (fermented) by brewers yeast, however, they need to be broken down by mash enzymes into chunks of two molecules (maltose) or just one molecule (glucose). These sugars are then extracted into the wort. In standard barley wort, maltose makes up about half of all wort sugars, while straight glucose makes up no more than one-tenth of all sugars. The remaining 40 percent of sugars are too complex to be fermentable by most yeast and tend to remain in the beer as residual sweetness ... and thus “carbs”! The objective for the low-carb brewer, therefore, is to make a “non-standard” wort, and to do this requires the conversion in the mash of as many starches as possible into fermentable sugars and as few starches as possible into unfermentable sugars.

To accomplish this, first note the connection between enzyme activity and temperature ranges:

Starch converting mash enzymes are also called diastatic enzymes. There are two types of diastatic enzymes, á-amylase and â-amylase. The enzyme á-amylase breaks starch molecules into complex, mostly unfermentable sugars, while the enzyme â-amylase breaks both starches and complex sugars into simple, fermentable sugars. The enzyme á-amylase (the complex-sugar maker) starts to show activity at around 140° F (60° C), reaches its peak performance at around 162° F (72° C), and virtually ceases all activity at around 176° F (80° C). The enzyme â-amylase (the simple-sugar maker), by contrast, starts to show activity at around 104° F (40° C), reaches its peak performance at around 149° F (65° C), and virtually ceases activity at around 158° F (70° C).

From these temperature values follow three logical requirements for a low-carb beer:

  1. We want to keep the mash as close to the optimum â-amylase temperature of 149° F (65° C) as possible so that we produce almost exclusively simple, fermentable sugars. We recommend a saccharification rest at this temperature of at least 45 minutes.
  2. Because, at a mash temperature of 149° F (65° C), á-amylase is still 13°F (7°C) below its peak performance, but is already within its active range, we can INCREASE the amount of starch conversion into simple sugars (and thus DECREASE the amount of carbs in the finished beer) by the adding an Alpha Amylase preparation to the mash.
  3. After the saccharification rest, move the mash as quickly as possible past 158° F (70° C), when â-amylase enzymes stop working, to a mash-out temperature of roughly 172°F (78° C), when á-amylase enzymes slow down .

To understand the eventual amount of carbs in your beer we must finally understand the metabolism of the yeast. The amount of carbs in your finished beer is influenced by the type of yeast you use. Here is how that logic works for the carb-conscious set: 

 Ales: Ale yeast ferments monosaccharides (glucose) and disaccharides (mostly maltose and some melibiose) up to roughly 50% of the starches that are naturally in the grain.
Lagers: Lager yeasts ferment monosaccharides and disaccharides as well as some trisaccharides (maltotriose and raffinose) for an additional roughly 5% of the original carbs in the grain. Trisaccharides are oligosaccharides (complex sugars) that contain three linked monosaccharides.

Conclusion: If you want to make a really low-carb beer, mash primarily for â-amylase activity, rest thoroughly, raise the temperature to the mash-out quickly past the peak á-amylase temperature, sparge fast, make sure you leave the unconverted starches in the spent grain instead of leaching them into the wort, and use of an Alpha Amylase preparation in the mash.

And there you have it...