Sugar alcohols are made primarily through two methods: catalytic hydrogenation, which adds hydrogen to a sugar molecule under high pressure, and microbial fermentation, which uses yeast to convert sugars into sugar alcohols naturally. The specific process depends on which sugar alcohol is being produced. Most commercial sugar alcohols like sorbitol, xylitol, and maltitol are made through hydrogenation in industrial facilities, while erythritol is almost always made through fermentation. These are not processes you can replicate in a home kitchen, but understanding how they work helps clarify what these sweeteners actually are and why they behave differently from regular sugar.
What Sugar Alcohols Actually Are
Despite the name, sugar alcohols contain no ethanol and won’t get you drunk. They’re a class of carbohydrate where the sugar molecule has been chemically modified so that a specific oxygen-containing group (called a carbonyl) is replaced with a hydrogen-oxygen pair. This small structural change is what makes sugar alcohols taste sweet but resist full digestion in your gut. The result: fewer calories and a much smaller effect on blood sugar than table sugar.
The FDA permits sorbitol, xylitol, erythritol, maltitol, mannitol, and lactitol for use as sugar substitutes in food. Each one starts from a different sugar source and follows a slightly different production path, but the underlying chemistry is similar across the board.
Catalytic Hydrogenation: The Main Method
Most sugar alcohols are produced through catalytic hydrogenation, a process that forces hydrogen gas into a sugar molecule under controlled heat and pressure. The process starts with a concentrated syrup of a specific sugar. For sorbitol, the starting sugar is glucose. For xylitol, it’s xylose, a sugar extracted from the hemicellulose in plant fibers like corn cobs and birch wood. For maltitol, the starting material is maltose.
The sugar syrup is loaded into a pressurized reactor along with a metal catalyst, most commonly a type called Raney nickel. This catalyst is favored across the industry for its low cost, high versatility, and effectiveness at driving the hydrogen into the sugar molecule. Inside the reactor, hydrogen gas is pumped in at high pressure while the temperature, pH, and reaction time are carefully controlled to maximize yield. The hydrogen atoms attach to the sugar’s carbonyl group, converting it into a hydroxyl group and transforming the sugar into its corresponding sugar alcohol.
After the reaction, the catalyst is filtered out and the resulting syrup is purified, concentrated, and often crystallized into the powder you’d find on store shelves. The variables that matter most during this process are temperature, pressure, and pH, since small changes affect both the speed of the reaction and how much of the starting sugar actually converts to the desired product rather than unwanted byproducts.
Fermentation: How Erythritol Is Made
Erythritol takes a completely different route. Instead of high-pressure chemistry, it’s produced by feeding glucose (usually from corn starch) to specific strains of yeast or fungi, which naturally convert the sugar into erythritol as a metabolic byproduct. The yeast genera most commonly used include Yarrowia, Moniliella, Candida, and several others. Researchers have also used mutagenesis and genetic engineering to develop strains that produce erythritol more efficiently.
The fermentation takes place in large bioreactors where the yeast cultures are kept at controlled temperatures and fed a steady supply of glucose syrup. Over the course of the fermentation cycle, the organisms consume the glucose and secrete erythritol into the surrounding liquid. Once fermentation is complete, the broth is filtered to remove the yeast cells, then purified and crystallized. This biological approach is one reason erythritol is often marketed as a “natural” sweetener, even though the final product goes through significant industrial processing.
Mannitol: Extraction From Seaweed
Mannitol has a unique production history. It’s one of the most abundant energy-storage molecules in nature and is found in especially high concentrations in brown seaweed. Commercially, mannitol can be extracted directly from seaweed biomass. In one established method, milled brown seaweed (commonly Laminaria hyperborea) is mixed with hot water at roughly 70°C, the pH is lowered to about 3.5 with acid, and the mixture is incubated for two to three hours. After centrifuging, the liquid extract contains measurable mannitol, around 4.7 grams per liter from a simple water extraction and over 7 grams per liter from a more thorough hydrolysis process.
Today, mannitol is also produced through catalytic hydrogenation of fructose, similar to how sorbitol is made from glucose. But the seaweed extraction route remains notable because it’s one of the few sugar alcohols that can be sourced from a whole food rather than synthesized entirely in a factory.
Why You Can’t Make Them at Home
If you were hoping for a DIY recipe, the short answer is that sugar alcohol production requires either industrial hydrogenation equipment (pressurized reactors, metal catalysts, hydrogen gas) or controlled microbial fermentation setups with specific yeast strains and purification systems. Neither is practical or safe outside a laboratory or manufacturing facility. Hydrogen gas is flammable and the pressures involved are dangerous without proper equipment, while fermentation with wild or uncontrolled yeast strains would produce unpredictable results and potential contaminants.
Home fermentation can produce ethanol (as in beer or wine), but the metabolic pathways that generate sugar alcohols like erythritol require very specific organisms under tightly managed conditions. The separation and purification steps alone, removing the sugar alcohol from the fermentation broth in pure crystalline form, require equipment beyond what a home setup can offer.
How Different Sugar Alcohols Compare
The production method influences the final product’s properties, but the biggest practical differences between sugar alcohols show up in two areas: blood sugar impact and digestive tolerance.
Erythritol has a glycemic index of 0 and an insulinemic index of just 2, meaning it has virtually no effect on blood sugar or insulin. Xylitol has a glycemic index of 13 and an insulinemic index of 11, still far below regular sugar. Maltitol, at a glycemic index of 35 and insulinemic index of 27, is the closest to sugar among common sugar alcohols and can cause a noticeable blood sugar response in people managing diabetes.
Digestive tolerance follows a dose-response curve. Most adults can handle 20 to 50 grams of sugar alcohols per day before experiencing bloating, gas, or diarrhea, though the exact threshold varies by the specific sugar alcohol. Erythritol is the best tolerated because most of it is absorbed in the small intestine and excreted in urine rather than reaching the large intestine where fermentation causes gas. Children and people with irritable bowel syndrome have significantly lower tolerance thresholds and are more prone to symptoms at smaller doses.
The Raw Materials Behind Each Type
Understanding what goes into each sugar alcohol helps demystify ingredient labels:
- Sorbitol is made from glucose, typically derived from corn starch. It’s the most widely produced sugar alcohol and shows up in everything from toothpaste to sugar-free candy.
- Xylitol starts as xylose, extracted from hemicellulose in corn cobs, birch wood, or other fibrous plant material. The xylose is then hydrogenated into xylitol.
- Erythritol begins as glucose from corn starch, which is fermented by yeast rather than chemically hydrogenated.
- Maltitol is produced by hydrogenating maltose, a sugar derived from starch.
- Mannitol can come from the hydrogenation of fructose or from direct extraction of brown seaweed.
In every case, the starting material is a naturally occurring sugar. The production process modifies that sugar’s molecular structure just enough to change how your body digests and absorbs it, cutting calories roughly in half (except for erythritol, which has about 0.2 calories per gram compared to sugar’s 4) while preserving most of the sweetness.