Does Sugar Reduce Moisture Content? The Science Behind Its Hygroscopic Power

October 31, 2025 •

4 min read

Food science reveals a fascinating paradox: the dry, crystalline substance known as sugar is technically a powerful "wet ingredient" due to its hygroscopic nature. This inherent quality, meaning it attracts and holds moisture, is the definitive answer to the question: does sugar reduce moisture content? Yes, it does, by binding water molecules and significantly impacting the moisture levels in food.

Quick Summary

Sugar reduces moisture content by acting as a humectant, binding free water molecules and lowering water activity. This process inhibits microbial growth, extends the shelf life of food, and influences the texture of baked goods.

Key Points

Hygroscopic Nature: Sugar is naturally hygroscopic, meaning it attracts and retains moisture from its surrounding environment, whether it's the air or other food ingredients.
Reduces Water Activity: By binding free water molecules, sugar lowers a food's water activity, making it an unsuitable environment for microbial growth.
Osmotic Preservation: In high concentrations, sugar creates a hypertonic solution that draws water out of food and microorganisms, a process known as osmosis.
Extends Shelf Life: The reduction in water activity acts as a natural preservative, inhibiting spoilage and allowing high-sugar products like jams to last longer.
Maintains Softness in Baking: As a humectant, sugar retains moisture in baked goods like cakes, preventing them from drying out and keeping them tender and soft.
Tenderizes Baked Goods: By competing with flour for water, sugar limits gluten formation, resulting in a more delicate and tender crumb structure.

The Hygroscopic Nature of Sugar

Sugar is a powerful humectant, a substance that attracts and retains moisture. This property is crucial in food science and explains its function far beyond just a sweetener. The chemical structure of sugar molecules allows them to form strong hydrogen bonds with water molecules, effectively trapping them and making them unavailable for other processes, including microbial growth. This is why brown sugar, which has a higher moisture content, can quickly harden when exposed to air as it pulls moisture from the atmosphere and binds with its own crystals.

How Sugar Lowers Water Activity

The key mechanism by which sugar reduces moisture content is by lowering the water activity ($a_w$) of a food product. Water activity is a measure of the unbound, free water available for microorganisms like bacteria, mold, and yeast to use for growth. By binding up free water molecules, sugar creates an environment where there is less available water, making it difficult for these spoilage organisms to survive and multiply. This is an ancient and highly effective method of preservation, used for centuries in making jams, jellies, and candied fruits.

The Osmosis Effect

In highly concentrated sugar solutions, an osmotic effect occurs. When food with lower sugar concentration is placed in a high-sugar liquid, water is drawn out of the food's cells and into the surrounding solution to balance the concentrations. This dehydration process is what allows for the preservation of fruits and vegetables in sugar syrups or for the curing of meats with both sugar and salt. The microorganisms within the food also experience this osmosis, losing vital water from their cells and effectively becoming dehydrated and inactive.

Sugar's Crucial Role in Baking

In baking, sugar's moisture-controlling properties are vital for achieving the desired texture, freshness, and shelf life. Beyond just sweetness, it influences the final product in several ways.

Moisture Retention and Softness

Sugar binds water molecules, keeping cakes and muffins soft and moist for longer periods.
Products with higher sugar content tend to resist staling, extending their shelf life significantly.
Bakers can use simple sugar syrups to re-moisten a dry, over-baked cake.

Tenderizing Effect

Sugar competes with flour for water, which limits the development of gluten.
This results in a more tender and delicate crumb texture in cakes and other baked goods, rather than a tough, chewy one.

Influence on Structure and Leavening

When creamed with butter, sugar's sharp crystals create tiny air pockets that expand during baking, contributing to the lift and volume of a cake.
Sugar stabilizes whipped egg foams, reinforcing the air bubbles and preventing collapse, essential for light meringues and soufflés.

Sugar vs. Salt: A Comparison of Moisture Control

Both sugar and salt are used as preservatives due to their ability to lower water activity. However, they achieve this effect with different efficiencies and results.


Feature	Sugar (Sucrose)	Salt (NaCl)
Hygroscopic Effect	Highly hygroscopic, attracts and binds water molecules.	Also hygroscopic, but much more effective at lowering water activity by weight.
Preservation Mechanism	Creates a hypertonic environment, drawing water out of cells via osmosis.	Creates a hypertonic environment, drawing water out of cells via osmosis.
Resulting Flavor	Sweet, used for jams, jellies, and confectionery.	Salty, used for curing meats and vegetables.
Concentration for Effect	Requires a higher weight percentage (approx. 55% solution) to achieve a similar water activity reduction as salt.	More effective at lower weight concentrations for reducing water activity.
Effect on Texture	Contributes to a soft, moist texture in baked goods and gelling in jams.	Adds firmness to cured foods; can make baked goods dense if too much is added.

The Role in Extended Shelf Life

The reduction of water activity by sugar is directly responsible for prolonging the shelf life of many products. By inhibiting the growth of microorganisms, foods like jam, honey, and certain types of confectionery can be stored for extended periods without refrigeration. This natural preservative effect has been a cornerstone of food preservation for centuries and remains an important function today. Even in baked goods, the moisture retention provided by sugar means the product stays fresh and tender for a longer duration, reducing food waste. For further reading on the science behind food preservation techniques, an excellent resource can be found at the UC Davis Food Safety website.

Conclusion

In conclusion, sugar definitively reduces moisture content through its hygroscopic properties, which allow it to bind water molecules and lower the water activity of food. This powerful humectant effect is a fundamental principle in food science, explaining its long history as a natural preservative and its multi-faceted role in baking. By controlling moisture, sugar inhibits microbial spoilage, influences the texture of baked goods, and extends shelf life, proving its functionality is far more complex and essential than simply adding sweetness.

Frequently Asked Questions

Sugar preserves food by binding free water, a process that lowers the food's water activity. This makes the environment too dry for microorganisms like bacteria and mold to grow and multiply, thereby preventing spoilage.

Sugar acts as both a humectant and, in effect, a desiccant. As a humectant, it attracts and retains moisture. When used in high concentrations, it pulls moisture from other substances and microorganisms, effectively dehydrating them, similar to how a desiccant works.

In baked goods, sugar's hygroscopic nature holds onto moisture, preventing them from becoming dry and stale. This moisture retention contributes to a softer, more tender, and moist texture in cakes, cookies, and other confections.

Brown sugar contains more moisture than white granulated sugar due to the presence of molasses. This makes brown sugar naturally more moist and more prone to clumping when stored incorrectly, as it continues to attract and absorb moisture from the air.

Both sugar and salt reduce moisture activity, but salt is more effective on a weight-for-weight basis. Sugar requires a higher concentration to achieve the same preservative effect as salt. While salt is used for curing, sugar is favored for jams and sweet confections.

Sugar is often called a 'wet ingredient' in baking because of how it behaves and interacts with liquids. It dissolves into the wet ingredients, and its hygroscopic nature allows it to bind water, influencing the overall moisture, texture, and structure of the final product.

Reducing the sugar in a recipe can lead to a drier, denser, and less tender baked good. Since less sugar is available to bind moisture and inhibit gluten, the final product may also stale faster and have a reduced shelf life.