How do you convert starch to sugar?

December 6, 2025 •

2 min read

Nearly all industrial-scale conversion of starch to sugars today is performed using enzymes, a shift from older acid-based methods. This article explains how you convert starch to sugar through different hydrolysis techniques, for both large-scale production and smaller kitchen experiments.

Quick Summary

Starch is converted to sugar via hydrolysis, a process accelerated by enzymes like amylase or by using strong acids. The reaction breaks down complex carbohydrate chains into simpler, sweet-tasting sugars like glucose and maltose.

Key Points

Enzymatic Conversion: Uses specific amylase enzymes (alpha-amylase, glucoamylase) for precise and efficient starch hydrolysis, commonly used in industrial food production.
Two-Step Enzymatic Process: Involves liquefaction (breaking starch into smaller dextrins) and saccharification (converting dextrins into simple sugars like glucose).
Acid Hydrolysis: An older, less controlled method that uses strong acids and heat to break down starch, often resulting in lower yields and undesirable byproducts.
At-Home Method: Achievable by using natural enzymes found in malted grains (like barley) mixed with warm water, a process known as mashing.
Key Enzymes: Alpha-amylase liquefies starch, while glucoamylase saccharifies it to glucose; beta-amylase can also be used to produce maltose.
Application in Brewing: The conversion of starch to fermentable sugars is a crucial step in producing alcoholic beverages from grain.
Controlled Environment: Both methods require careful management of temperature and pH to optimize the conversion reaction.

Enzymatic Conversion Method

Modern food production favors enzymatic conversion for its efficiency. This method involves stages with specific conditions for enzymes.

Starch Liquefaction

Starch mixed with water is heated to gelatinize it, making it accessible to enzymes. Heat-stable alpha-amylase is added, breaking starch into smaller dextrins and oligosaccharides and reducing viscosity. Temperature and pH are controlled for enzyme activity.

Saccharification

The mixture cools, and glucoamylase is added. This enzyme breaks dextrins into glucose, increasing sweetness. Beta-amylase can also be used for maltose production.

The Role of Amylase Enzymes

Alpha-Amylase: Breaks internal bonds, used in liquefaction.
Beta-Amylase: Cleaves off maltose from chain ends.
Glucoamylase: Produces glucose by removing units from chain ends.

Acid Hydrolysis Method

This older method uses strong acid and high heat. Heating starch with acids like hydrochloric or sulfuric acid breaks glycosidic bonds. This method is less specific than enzymatic conversion and can create undesirable byproducts. Neutralization after the process produces salts. It's still used where equipment can handle corrosive conditions.

At-Home Starch to Sugar Conversion

Converting starch at home is possible using enzymes from malted grains, forming the basis of brewing.

Steps for a Simple Starch Mash

Prepare Starch: Use a source like corn or malted barley. Milling increases surface area.
Mashing: Mix milled grains with water. Maintain 140°F-150°F (60°C-66°C) for enzyme activity.
Enzymatic Action: Malted barley's enzymes convert starch to sugars. Commercial enzymes can also be added.
Hold and Stir: Maintain temperature for 60-90 minutes.
Separate and Use: Strain the sugary liquid (wort) from solids. Use as a sweetener or for fermentation.

Enzymatic vs. Acid Hydrolysis Comparison Table


Feature	Enzymatic Hydrolysis	Acid Hydrolysis
Mechanism	Catalyzed by specific enzymes (amylases) that cleave bonds.	Catalyzed by strong acids (HCl, H2SO4) under high heat.
Efficiency	Very high yield and specific sugars produced.	Lower yield; can produce undesirable byproducts.
Control	Precise control over sugar type (glucose, maltose, etc.).	Less control over the final sugar profile.
Byproducts	Minimal to no side-reactions or off-flavors.	Can create undesirable byproducts and off-flavors.
Conditions	Mild temperature and pH conditions.	Corrosive, high-temperature, high-pressure conditions.
Safety	Safer for handling and end-product purity.	Requires handling strong, dangerous acids.
Equipment	Requires standard heating and mixing equipment.	Needs specialized, acid-resistant equipment.
Cost	Enzymes can be costly, but the process is highly efficient.	Acids are cheap, but purification and safety costs add up.

Conclusion

Starch to sugar conversion is vital for food and biofuel. Enzymatic conversion is generally preferred for its control and efficiency, while acid hydrolysis is an older method with specific industrial uses. Home converters can use the enzymatic method with malted grains.

Learn more about the specific functions of amylase enzymes at the National Institutes of Health.

Frequently Asked Questions

Amylase is the primary enzyme used to convert starch into sugars. Different types of amylase, such as alpha-amylase and glucoamylase, perform specific roles in breaking down starch chains.

Yes, starch can be converted to sugar at home by using naturally occurring enzymes. The most common method involves mashing malted grains (like barley) in warm water, a process used in brewing and distilling.

Liquefaction is the first step where alpha-amylase breaks down large starch molecules into smaller dextrins, reducing the viscosity. Saccharification is the second step, where glucoamylase further breaks these dextrins down into simple sugars like glucose.

Enzymatic conversion offers a higher yield, produces fewer undesirable byproducts, and provides much more control over the type of sugar produced. It also operates under milder conditions, making it safer and less corrosive to equipment.

Starch is a polymer of glucose, so the primary end product of complete hydrolysis is glucose (dextrose). However, depending on the enzymes used, intermediate sugars like maltose and maltotriose can also be produced.

Successful enzymatic conversion requires controlling factors like temperature and pH, which affect enzyme activity. Specific enzymes have different optimal conditions; for example, high-temperature amylases are used in the liquefaction phase.

The enzymatic conversion reaction is typically stopped by terminating the enzyme activity. This can be done by heating the mixture to a high enough temperature to denature the enzymes or by adjusting the pH outside of their optimal range.