Sugar is a fundamental element of making hard cider. Without sugar, yeast couldn’t ferment juice and produce ethanol so we wouldn’t have cider. We also wouldn’t have vinegar because vinegar is formed from the ethanol produced by the sugar. Isn’t it interesting how a single simple compound can have such a dramatic impact on human life. Historically, we have used fermentation as a means to preserve and sanitize. Cider, mead beer, and wine were ways to ensure water was safe to drink and vinegar has long been used to preserve food. But, is sugar really a single simple compound?
The short answer is no. There are many types of sugars even though most sugars have the same core compounds: Carbon, Hydrogen, and Oxygen. Some even have the same chemical formula even though the physical structure of the actual molecule is different. For example, glucose and fructose both have the chemical formula C6H12O6 but, the carbon, hydrogen, and oxygen atoms are arranged differently. This different arrangement is what makes the compounds unique. Similarly complex, sugar are often called different things. Glucose and fructose are hexoses. They are also sometimes called simple sugars or reducing sugars. When we say sugar, it sounds simple. The reality is that discussing sugar can be quite complex. Here is a table of common sugars and some of their key characteristics.
|Glucose||Monosaccharide||C6H12O6||Reducing – Aldoses|
|Fructose||Monosaccharide||C6H12O6||Reducing – Ketoses|
|Galactose||Monosaccharide||C6H12O6||Reducing – Aldoses|
|Mannose||Monosaccharide||C6H12O6||Reducing – Aldoses|
|Sorbose||Monosaccharide||C6H12O6||Reducing – Ketoses|
Why is this important to a home craft cider maker? Because just like not all sugars are the same, not all yeast are the same. The attenuation number found on most beer yeasts but not on wine yeast is an example of how yeast are different. Many beer yeasts have undergone domestication causing it to change its genetic makeup in order to better survive in a human environment. One of those changes is its the ability to process malt sugars like maltose. Knowing that beer contains a significant amount of malt sugars from the grain, the attenuation number found on the yeast represent how efficient that yeast strain is in processing these malt sugars. Knowing what sugars are in your juice or must, will help you understand how the yeast you select will react to it. For apple juice, which is high in fructose, selecting yeasts that prefer glucose or don’t process fructose should result in higher residual sugars. This highlights the need for more research and ultimately options for true cider yeasts.
Apple juice isn’t like grape juice or wort used to make beer so just like wine and beer have yeast suited to there production, cider should also have yeast that match well with the sugars in the juice and goal for the end cider. If you want a dry cider with maximum alcohol levels, Saccharomyces cerevisiae yeast strains that are often used for wine would probably be best. But, if you want a cider with some residual sweetness, you should look for non-Saccharomyces strains like Lachancea thermotolarens, Pichia kluyveri, or similar non-standard yeast. The challenge is finding these strains. Wild fermentations will have them as they are naturally found on apples but so are many other strains and your ability to control the fermentation is reduced. Since yeast isn’t the focus of this article, research PricklyCider.com for non-Saccharomyces yeasts to explore this concept more. The main point is that you need to understand sugars and how a monosaccharide is different from a disaccharide or what is meant when someone says a sugar is a reducing sugar. Understanding sugars will help you understand how they react with yeast. This will help you make better cider. So, let’s explore some common terminology of sugars and how they relate to making cider.
- Monosaccharides versus Disaccharides
- Reducing versus Non-Reducing
- Hexose and Dextrose
Monosaccharides versus Disaccharides
Mono means one or single and saccharide comes from the Greek word for sugar so a monosaccharide is a single sugar or often called a simple sugar. The prefix of ”di” in disaccharides means two or dual. So if a monosaccharide is a single or simple sugar, a disaccharide is a more complex sugar. It is actually two monosaccharide sugars combined. Glucose is a monosaccharide and sucrose is a disaccharide. Sucrose consists of a glucose molecule and a fructose molecule. Here is a table of common disaccharides and their molecular components.
|Disaccharide||Molecule 1||Molecule 2|
Sucrose is actually what most of us think of when someone mentions sugar. It is often called table sugar. It is commonly derived from sugar cane or sugar beets. Sucrose is found in apples. However, it is usually only the third most common sugar behind fructose and glucose. Disaccharides generally have 12 carbon atoms versus only 6 carbon atoms for monosaccharides. For fermentation, yeast generally need monosaccharides, which means disaccharides need to be broken down into their monosaccharide compounds. This generally occurs through enzyme reactions called disaccharidases. Fermentative yeasts, like Saccharomyces, Lachancea, and Pichia species, generally have the enzyme structure to process sucrose but most can’t process lactose. Maltose can be processed by some yeasts but not all. Note that not all monosaccharides can be fermented. Yeast have different genes that can enable or inhibit the processing of different sugars. Saccharomyces cerevisiae yeasts have been sequenced and the genetic characteristics are well understood. While some Non-Saccharomyces yeast have been sequenced, many are still unknown and understanding whether they will or will not process certain sugars requires testing.
Reducing versus Non-Reducing
You may see some sugars called reducing sugars. The term reducing means that sugar is capable of donating an electron. This occurs during a reductive-oxidative reaction. Oxygen can react with reducing sugar creating new compounds. The oxygen is the oxidizing agent while the sugar is the reducing agent. A common type of reductive-oxidative reaction in cider and wine are Maillard reactions. These often occur during aging but can also be induced with increases in temperatures. With Maillard reactions, a reducing sugar combines with an amino acid though oxygen must also be present. The sugar is the reducing agent because it donates the electron and oxidizes.
As indicated in the above table, all monosaccharides are reducing sugars though there are two types. Monosaccharides can be aldoses or ketoses reducing agents. These types define the element of the sugar compound that donates the electron. Aldoses have an open aldehyde group while ketoses have an open ketone group. Aldoses type sugars are more readily reduced since ketoses type sugar must first have the ketone group changed into a aldehyde group. Not all disaccharides are reducing sugars. Reducing or non-reducing is really about how stable the compound is. Sucrose is a non-reducing sugar because both its carbon bonds are strongly made while other disaccharides like lactose have one strong carbon bond and one weak bond. Reducing sugars play a part in how cider will age, especially if it has access to oxygen because of headspace, dissolved oxygen, or even oxygen diffused through the cork.
Hexose and Dextrose
You may also see sugars called hexose or dextrose. Hexoses simply means the sugar is a monosaccharide with 6 carbon atoms. The prefix “Hex” is Greek for six. You can find the term hexose used in the cider or wine industry when discussing the group of monosaccharides with 6 carbons like glucose, fructose, galactose, and such. Sucrose and other disaccharides are not hexose.
The other sugar you might see referenced is dextrose but this might be more common in the beer and distillation industry. Dextrose is chemically identical to glucose. That means it is a monosaccharide, a simple sugar, a reducing sugar, and since it has 6 carbons, a hexose. Dextrose is simply glucose that has been derived from corn. Corn syrup contain dextrose. Yeast will process dextrose just like glucose.
(1) R. Lagunas, Sugar transport in Saccharomyces cerevisiae, FEMS Microbiology Reviews 104, 229-242, 1993
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