The basic concept of brewing is that yeast digests sugar, and produces (among other things) ethyl alcohol and carbon dioxide. Ideally, the flavor of the resulting alcohol will emulate the flavors of the various ingredients used to produce it. However, sugar is not a mere ingredient. There are several different types of sugar – generally any carbohydrate ending in -ose is a sugar – as well as sugar compounds. All sugars, however, are composed of carbon, hydrogen, and oxygen molecules. Understanding how your selected yeast reacts with the sugars in your wort or must is essential to predicting the most likely finished flavor of any fermented beverage, and is a great aid in recipe formulation.
Brewers and vintners use several different manifestations of sugar in their processes. These include but aren’t limited to cane or beet sugar, fruit or fruit juice, molasses, honey, malt, corn sugar or syrup, rice syrup, milk sugar, and palm or maple sugar. Each of these is used for a particular effect, whether to increase alcohol content, substitute for a more expensive ingredient, or flavor the finished beverage. By understanding the characteristics of each, and how each will react both with the yeast and with other ingredients, we can choose how and when to introduce each to the batch for maximum desired effect.
Sugars can be broadly classified as either simple or complex.
Simple sugars by definition are those that have the simplest chemical makeup – monosaccharides (made up of a single sugar molecule) and disaccharides (made up of two sugar molecules with one water molecule taken away in the bonding.) These types of sugar are the easiest to digest, and therefore are the easiest for yeast to process.
Complex sugars, commonly known as starches, are those sugars made by the chaining of multiple simple sugar molecules. These types of sugars are more difficult to digest, as the bonds between sugar molecules must first be broken down (the process brewers refer to as conversion) before the resulting simple sugars can be processed by the yeast. Complex sugar compounds may require the addition of particular enzymes in order to break down the molecular chains before the yeast can do its work.
We will first look at the simplest sugars available to the average brewer.
The most common monosaccharides available to the brewer are glucose and fructose. Both of these sugars are very basic and will be aggressively attacked by yeast early in the fermentation process.
Glucose (also known as dextrose) is the most common sugar compound, and is the one found most commonly in the human body. It is found in most plants as a principle byproduct of photosynthesis. This is also the most common sugar used as a food additive. The most common form of glucose used by brewers is corn sugar.
Fructose occurs most naturally in fruit, and is the sweetest tasting of the sugars. We see this sugar used extensively in processed foods as a principle component of high-fructose corn syrup.
A third monosaccharide called galactose does not exist in a free form, and is only made available through the breaking down of disaccharides or compounds. Galactose is not generally available to the brewer except as a byproduct of conversion.
The most common disaccharides are sucrose (the principle ingredient in table sugar), maltose (the most common sugar found in grains), and lactose (the principle sugar found in dairy products.) Each of these sugars is comprised of a combination of two monosaccharides with the subtraction of a water molecule. The bond holding these two molecules together is defined as a hemiacetal linkage. During the fermentation process, the yeast must first break the linkage to reduce the compound to its glucose, fructose, and/or galactose components in order to then process those base sugars. The key feature of this process is the conversion of a hemiacetal and an alcohol to an acetal, with the concurrent release of a molecule of water, the oxygen atom of which is the actual molecular link. The acetal byproducts are called glycosides, and if formed in excess may impart a buttery flavor to the finished brew.
Sucrose is made up of one molecule each of glucose and fructose, and occurs naturally in many plants, including sugar cane, beets, and carrots. Table sugar and most cooking sugars are commonly sucrose. In brewing, sucrose is used most commonly in wines and ciders, and actually imparts a cidery flavor if used to excess. Because of the fructose component, sucrose is the easiest of the disaccharides for yeast to process.
Maltose is produced in many grains, and forms during germination. It is made up of two molecules of glucose. Maltose is the most common sugar used in the production of ales and lagers, and has a largely neutral although vaguely starchy flavor. It is also the most common sugar produced when certain enzymes are applied to the starches in grain during the mashing process.
Lactose is made up of one molecule each of glucose and galactose, and is the principle sugar found in dairy products. It is commonly and incorrectly identified as a non-fermentable sugar. In truth, lactose will ferment slowly only with specific strains of yeast, although its processing can be accelerated with the use of enzymes such as lactase. Lactose is often used to impart a sweet component to farmhouse ales or stouts. It is also the principle sugar used in the production of kumis.
Invert sugar or confectioners sugar is also available to the brewer, generally in the form of Belgian candi sugar. Invert sugar is simply sucrose that has been chemically or thermally converted to its base form of glucose and fructose, then recrystallized for storage. Invert sugar will have slightly more residual sweetness and slightly less cidery flavor than ordinary sucrose, and as such is useful in certain beers.
Complex sugars take the form of oligosaccharides (molecular chains of between three and nine simple sugar molecules, commonly known as starches) and polysaccharides (molecular chains of ten or more simple sugar molecules, commonly known as fiber.)
Fiber is not suitable for brewing, so we will not discuss it here. Starch compounds may contain as few as three sugar molecules or as many as nine, and may include bonding with non-sugar elements such as ethers and aldehydes. Starches are bonded in such a way as to make it nearly impossible for yeast to process without first breaking down the chains through enzymatic hydrolysis.
The two most common starch compounds in any food product are amylose and amylopectin.
Amylose is a polymer starch made up of multiple glucose molecules bonded in an oxygen chain. It makes up about 30 percent of the starch stored in plants, including grains used in brewing. When introduced to the enzyme alpha-amylase (note the similarity in the name), the oxygen bonds are broken, producing the oligosaccharide maltotriose (triple-bonded maltose) and simple maltose. Note that amylose will appear a dark blue when introduced to iodine… a common test brewers use to determine if conversion has taken place.
A common byproduct of amylose conversion is dextrin, which is produced during the mashing process (the hydrolysis of the amylo-starches.) Dextrin does not ferment readily, but can contribute to the brewer’s desired end. Caramelization of dextrins in malted grains is what produces the unique flavor components of crystal malt, as well as contributing to the reddish hue of brews using crystal malt.
Malto-dextrin, also available commercially at most health food stores or brewing supply shops, is a type of amylose derived most commonly from corn and less so from wheat. Although it is not fermentable in its commercially available form, and has little inherent sweetness, it can be used to increase the body of a beer and improve head retention. It’s most common use is as a carbohydrate supplement for athletes.
Amylopectin is a polymer starch made up of multiple glucose molecules bonded in a branched oxygen chain. It makes up about 70 percent of the starch stored in plants, approaching 100 percent in corn, potatoes, and rice. The branching in the molecular structure of the compound allows various enzymes to attach themselves to the chain, making amylopectin more soluble and easier to degrade than amylose. When introduced to the enzyme beta-amylase, the oxygen bonds are broken and hydrolized, producing maltose and glucose.
Rice syrup, available in most health food stores, is actually modified amylopectin derived from rice grains, and thus consists largely of maltose and glucose, as well as dextrin. Rice syrup in its unmodified form is sometimes used as a non-fermentable to provide more body to a beer that has an otherwise low malt content. In its modified form, it is most often found in sake – a Japanese rice wine. A note for brewers shopping at conventional supply stores… rice syrup is not the same as rice syrup solids. The solids are the unmodified rice starches, unfermentable in their commercially available form.
Some sugars commonly referred to as complex are really just amalgamations of simple sugars blended with proteins and mineral compounds.
Honey is an example of an amalgamated sugar composite that contains other factors influencing fermentation. In addition to fructose, glucose, maltose, and sucrose compounds, honey contains a variety of amino acids (proteins), fiber, and trace minerals. Honey can be both an easy and a complicated sugar to ferment. The glucose and fructose are monosaccharides, but the maltose and sucrose components must be broken down prior to fermentation being able to take place. This added step puts the yeast at a significant disadvantage, and can be witnessed in the extended period of time between pitching the yeast and seeing significant activity in the fermenter. For this reason, brewers will often add a yeast nutrient or energizer to promote a faster start and more aggressive primary fermentation cycle. Honey is the principle ingredient in the production of mead.
Molasses is a byproduct of the production of crystallized table sugar, and consists of sucrose, glucose, and fructose. Because sucrose is a disaccharide, the yeast will most likely process the glucose and fructose first before attempting to break the bonds between the molecules in the sucrose. When mixed with monosaccharide-based ingredients, the molasses will likely be processed later in the fermentation process, allowing many of the residual characteristics of the molasses to remain in the beverage. Molasses is often used in stouts to soften the harsh flavor of the darker grains, and is the principle ingredient in the production of rum.
Maple syrup derives from evaporation of water from tree sap, and is an amalgamation primarily of sucrose and water, with small quantities of glucose and fructose from the invert sugar resulting from the boiling. The large concentration of sucrose means that yeast will process maple syrup after the simpler sugars have been exhausted, leaving much of the maple character behind in the finished beverage. Non-sugar aspects of maple syrup include volatile organic compounds such as vanillin, hydroxybutanone, and propionaldehyde. Maple syrup also includes numerous phenolic compounds which impart a spicy or clove-like flavor when used in brewing, and may give a medicine-like flavor if present in excess.
So, now that we have a basic understanding of the more common types of sugars, how can we use this to our advantage in brewing? Very simply – by understanding the processes that the yeast, any added enzymes, and the heating or cooling processes have on the sugars themselves, we can modify our sequence of processes and our ingredients list to achieve desired results.
The first consideration as a brewer is the formulation of the recipe. The choice of fermentable and non-fermentable ingredients and the amounts in which they are used will significantly affect the flavor, body, and alcohol content of the finished beverage. Most brewers are aware of the basic effects of various sugars (briefly discussed above), but not necessarily the “why” behind those effects. By understanding the “why”, the brewer can make intelligent decisions on what types of sugars and starches they wish to build into their recipe. A desire for higher alcohol content in a lighter bodied beer warrants the addition of simpler sugars, while a fuller bodied beer with a moderate alcohol content might warrant the addition of complex or non-fermentable sugars. As shown with the sugar blends, the ancillary character of honey, molasses, maple syrup or other less common amalgamations may be a desirable effect for the beverage.
The second consideration is the timing of ingredients in the brewing process. Take, for example, the rice syrup. Rice syrup is a complex sugar that requires enzymes to break it down for fermentation. Those enzymes are active at the temperature ranges most commonly used in the mashing process, but are destroyed at higher temperatures – even if at that temperature for only a few minutes. Therefore, if the rice syrup is desired as a fermentable, it must be added with the enzymes in the mash tun. If the rice syrup is desired for its ability to add body without affecting flavor or alcohol content, it must be added in the boil. The amount of rice syrup added is also a consideration, as only small amounts are required in the latter case while significantly higher amounts are required in the former. Another example is the ongoing argument among meadhers on the benefits and detriments of using honey raw, pasteurized, or boiled. Raw honey will have a lighter color, more floral characteristics, and a greater influence on the overall flavor of the beverage while boiled honey will allow the brewer to rid the honey of detritus from the beehive, any remaining beeswax, and protein compounds. The desired end state of the beverage may influence the brewer’s choice regarding how to prepare and when to introduce the honey to the must/wort.
Also consider your choice of sugars based on the character each will impart on the finished beverage. Fructose and glucose/dextrose will be turned into alcohol quickly right from the start, and will add little character to the finished product in most cases. This is why corn sugar is mainly used as an alcohol booster in a variety of different beverage types. Sucrose will impart a cidery flavor, making it acceptable for ciders and wines, but abominable for beers. Maltose will almost certainly impart a cereal character to the beverage, making it perfect in beers and braggots, but largely undesirable in wines or other types of mead. The most complex sugars can be chosen more for their distinct flavors, aromas, and aftertastes rather than for their fermentability, as the bulk of the sugars, and therefore the characteristics associated with those sugars, will remain in the finished beverage.
The next consideration is the choice of yeast and yeast additives. As we saw with lactose, it may require a specific strain of yeast to properly break down this bonded sugar. In period, yeasts were cultured down from wild strains by being harvested from one batch for use in starting the next batch. Several generations of yeast barm might produce a yeast strain that is tempered to a specific sugar, simple or complex; but too much is left to chance. Modern science now has more than 120 strains of yeast available to brewers, some of which are cultured specifically for their ability to exploit bonded sugars. In addition, a variety of natural and chemical nutrients and energizers are available to assist the yeast in achieving a fast start and a strong primary ferment. The brewer should research the yeasts available, and choose the strain best suited to the ingredient list and the desired end state of the beverage. More advanced brewers will find a greater variety of strains with many subtle differences in the pitchable liquid strains available from commercial laboratories than are available in the somewhat limited selection of dry yeast sachets most commonly on the retail market.
The final consideration is in the actual fermentation. Beginning brewers are prone to boil everything together, stick it all the fermenter, pitch the yeast, and take what they get. The more advanced brewer will consider the timing of fermentation with the same level of concern as the timing of the mash and boil. Yeast by its very nature will move to ingest the simplest sugar molecules first, as they are the easiest for the yeast to process. Only when the simpler sugars are used up will the yeast proceed to the more complex sugars. By the time the yeast reaches the most complex sugars, it is likely that the majority of yeast cells in play are either ‘tired’ (near the end of their life cycle) or nearing the limits of their own alcohol tolerance. Remember that yeast is an organism that rushes towards its own demise in its efforts to produce ethanol as efficiently as possible. In many cases, this is the desired effect, as the simpler sugars are useful in providing the desired alcohol levels while leaving the more complex sugars to temper the beverage to the brewer’s taste.
As an example of this last phenomena, consider what happens when you make a straight mead – no additives or adjuncts. If you use the same amount of honey you would use for a melomel, you may in fact wind up with less of a honey flavor in the end result. This is because a melomel has fruit, which is full of fructose, which is a monosaccharide, while the honey is an amalgamation of mono and disaccharides. In the melomel, the yeast will go after the fructose first, and only move on to the honey when the fructose is exhausted. The end result is that there is more unfermented honey available in the melomel than in the traditional mead. The general fix for this is to add more honey per gallon of straight mead than you would use for a melomel in order to have the finished product exhibit a similar honey taste.
Now, consider just the melomel. Try this experiment: using the same ingredients (type and amount) and the same yeast, set up three one-gallon fermenters. In the first, add the honey and fruit right from the start. In the second, add only the honey in the primary, and add the fruit after moving the must to the secondary. In the third, add only the honey in both primary and secondary, and add the fruit after fermentation is complete and the yeast has reached its alcohol tolerance. You should notice distinct differences in the finished flavor based on the sugars available to the yeast at each stage of fermentation. In the first gallon, the fructose – along with much of the character of the fruit – will be processed early and rapidly, with the yeast only going after the honey once the fructose is gone. This leaves a more prominent honey character to the finished mead. In the second, you will likely see two distinct “primary” fermentations, with the tired yeast coming off the bonded sugars to find a base sugar introduced. This should cause a rejuvenated fermentation that will slow rapidly as the ethanol level approaches yeast tolerance. In the final gallon, the yeast will be at or very near its tolerance, and most of the character of the honey will be fermented out, while the fruit will remain as the principle flavor. You may see some rejuvenation of fermentation, but it will be extremely short-lived. The first example is probably closer in consistency and body to what most people would think of as a mead, while the latter will be much closer in characteristics to a wine or wine cooler.
Understanding which ingredients will impart which specific sugars and how each of those sugars will impact the finished beverage allows the discerning brewer to make intelligent choices both in recipe design and in processes. Additionally, understanding what each ingredient is designed to do and how it reacts with other ingredients in the batch allows the brewer to evaluate existing recipes rather than blindly following someone else’s possible mistakes.
The order in which yeast will process sugars:
Dextrose / Glucose
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