Have you ever stopped to think about what kind of sugars are found in the wort of your soon to be beer? Most homebrewers seem to focus on the enzymes found in the mash, such as the alpha and beta amylases. But all enzymes are doing are producing sugars. Sugars are carbohydrates, so let’s first learn about the different carbohydrates that are important to all brewers, beginner or experienced.
Sugars, starches, and dextrins are the main forms of carbohydrates that homebrewers should know about. In a brewer’s mash tun, starch is converted to sugars and dextrins. If you are an extract brewer, then the manufacturer of your malt extract already converted all the starch for you. All carbohydrates start with the basic building block of a monosaccharide (1-sugar unit) and can grow like a tree, connecting the monosaccharides into long and complex chains. Most of the sugars produced in the mash are based on glucose and glucose polymers (chains). If the glucose polymers grow big enough, we know them as starch, which is the form that plants like barley and wheat store their food reserves. A brewer’s mash is complete when there is no starch left in the wort, just sugars and dextrins.
There are three monosaccharides; glucose, fructose, and galactose. If you join two glucose molecules together, you form maltose. A glucose joined with a fructose makes sucrose while glucose and galactose together form lactose. As stated earlier, glucose and chains of glucose are really the main focus for brewers. Lactose will only be added as a specialty ingredient while sucrose and fructose make up only a small percentage of sugars in a mash.
As the chain length increases, so does the forms that the sugar can take, so generally scientists just call the next level up trisaccharides. Dextrins are a class of carbohydrates generally associated with unfermentable carbohydrates. Dextrins can be as small as three sugar units long and can extend to seventeen units. Meanwhile starch can contain over 10,000 monosaccharide units.
Why Is this Important?
During fermentation, the yeast will transform the majority of the sugars produced during the mash into ethanol and carbon dioxide. Brewer’s yeast is actually quite methodical in their approach to what they eat first. Yeast will go for simple monosaccharides first. Glucose and fructose are the simplest of sugars found in wort and account for approximately 15-20% of the carbohydrates found in a wort where no supplemental sugar was added. Next up on their list is sucrose, although sucrose levels are rather small, generally only 2-6% of the carbohydrates of a standard wort. The yeast need to chop the sucrose up into the glucose and fructose. Once the sucrose, fructose and glucose levels decrease appreciably, the yeast then begin to ramp up their consumption of maltose, which makes up the largest percentage of wort’s carbohydrates, generally in the 30-40% range. As maltose levels decline, then it’s time for the yeast to work on the final major sugar of fermentation, maltotriose, a trisaccharide made up of three glucose molecules and accounts for typically 15-20% of wort’s carbohydrates. If your yeast were stressed early in fermentation by lack of nutrients, oxygen or adequate pitching, it’s usually the switch to fermenting maltotriose when the yeast will stall on you. This will leave you with a sweet, underattenuated beer. Happy yeast generally make better beer since they make this final transition to fermenting the maltotriose easier. Providing a very high percentage of simple sugars early in the fermentation process can also lead to yeast struggling to switch to the fermentation of maltotriose.
In your wort, there will be a decent percentage of sugars and dextrins that are unfermentable by standard brewer’s yeast. The percentage of unfermentables depends largely on a brewer’s mash procedure, the yeast strain used, and supplemental sugar additions trying to weigh the beer’s balance one way or the other. In a standard mash, unfermentables account for 20-35% of the carbohydrates. This is why a standard attenuation (the percentage of sugars consumed by yeast) is in the 65-80% range.
The higher the level of dextrins and unfermentable sugars, the more viscous the beer. To reduce these levels, brewers often perform either an extended mash at a low single infusion mash temperature, or a step mash that allows enhanced maltose production. On the flip side, shortening the mash time and raising the mash temperature will increase the percentage of dextrins, generally classified as ‘alpha amylase limit dextrins.’ An enzyme known as limit dextrinase can chop up limit dextrins, but many standard single infusion mash temperatures are too warm for limit dextrinase. This is one reason that extended mashes in the 135 to 140 °F (57 to 60 °C) range can produce highly fermentable worts, since the limit dextrinase can work on chopping up these limit dextrins.
Learning the basics of wort’s carbohydrates and how yeast utilize them during fermentation can help you better understand how to control these factors to your advantage.