Why is aluminum sulfate in food? Exploring its uses and safety

October 30, 2025 •

4 min read

In the United States, the Food and Drug Administration (FDA) lists food-grade aluminum sulfate as "generally recognized as safe" (GRAS) for use in food when following good manufacturing practices. So, why is aluminum sulfate in food, and what specific functional roles does it play in processed foods like baked goods and pickled items? This article delves into its various applications and its safety profile.

Quick Summary

Aluminum sulfate serves multiple functional purposes in food production, including acting as a firming agent, leavening acid, and pH regulator. It is considered safe within regulatory guidelines.

Key Points

Firming Agent: Aluminum sulfate strengthens cell walls in vegetables and fruits, preventing them from softening during processing like pickling and canning.
Leavening Acid: As sodium aluminum sulfate, it is a key component in double-acting baking powders, providing a controlled rise during baking.
pH Regulator: It is used to adjust the acidity in foods and beverages, ensuring flavor stability and processing consistency.
GRAS Status: The U.S. FDA classifies food-grade aluminum sulfate as "Generally Recognized As Safe" (GRAS) for use within good manufacturing practices.
Low Bioavailability: Studies by organizations like EFSA and JECFA show that aluminum compounds have low bioavailability and are of no safety concern at authorized levels.
Multi-functional: Beyond firming and leavening, it also functions as a sequestrant and emulsifier, enhancing texture and stability in various products.

What is Aluminum Sulfate?

Aluminum sulfate, often referred to as alum, is a chemical compound with the formula Al₂(SO₄)₃. It is a water-soluble salt that typically appears as an odorless white powder or crystal fragments. While many people associate the term "alum" with the potassium-based version used in pickling or for medicinal purposes, aluminum sulfate itself is specifically known in the food industry as the food additive E520 in Europe. The compound is not found as a free element but rather in combination with other elements, and its production often involves reacting sulfuric acid with bauxite or aluminum hydroxide. The reasons it is added to food are purely technical, intended to improve texture, appearance, and stability, rather than adding any nutritional value.

Functional Roles in Food Processing

Aluminum sulfate is a versatile additive used in various food applications due to its unique chemical properties. Its functions include:

Firming Agent

One of the most common uses for aluminum sulfate is as a firming agent. In products like pickled cucumbers, candied cherries, and other processed fruits and vegetables, it helps maintain a crisp texture and prevents the food from becoming soft or collapsing during processing. It works by interacting with pectins in the plant cell walls, strengthening their structure and providing a firm bite that would otherwise be lost during the heat of canning or preserving.

Leavening Agent

In the baking industry, aluminum sulfate is primarily utilized in the form of sodium aluminum sulfate (SAS). It acts as a slow-acting, heat-activated leavening acid, typically used in double-acting baking powders. When combined with sodium bicarbonate, SAS is inactive at room temperature but releases carbon dioxide gas when heated in the oven, causing baked goods like cakes, biscuits, and muffins to rise. This controlled release of gas results in a lighter, more uniform crumb structure.

pH Regulator and Sequestrant

Food-grade aluminum sulfate also acts as a pH adjuster and sequestrant. It can be used to control the acidity levels in foods and beverages, such as regulating the pH in processed vegetables and clarifying sugar beet juices. As a sequestrant, it binds to trace metal ions, preventing them from interfering with the product's color, flavor, or texture over time.

Thickening and Emulsifying Agent

In certain food applications, aluminum sulfate is used as a thickening and emulsifying agent. For example, it can aid in the curdling and thickening of cheese. It helps to create a stable emulsion by helping to mix ingredients that normally would not combine smoothly, such as oil and water.

Safety Profile and Regulation

Like all food additives, aluminum sulfate has undergone extensive safety evaluation by regulatory bodies worldwide, including the U.S. FDA and the European Food Safety Authority (EFSA).

U.S. Regulation: The FDA has affirmed aluminum sulfate's status as Generally Recognized As Safe (GRAS) for use in food when used according to good manufacturing practices. This means that experts agree it is safe at the levels typically found in food products.
European Regulation: In Europe, aluminum sulfates (E520-E523) and sodium aluminum phosphate (E541) have been re-evaluated by EFSA. Based on the low bioavailability of aluminum compounds and conservative exposure estimates, EFSA concluded that these additives are of no safety concern at the current authorized use levels.

It is important to note that while acute ingestion of very large quantities can cause adverse effects like nausea or irritation, the amount used in food is very small and not considered a health risk for individuals with normal kidney function. Concerns about aluminum exposure from dietary sources have been extensively studied, and major bodies have concluded that it does not pose a significant risk at normal intake levels. For more information on food additive safety, refer to the EFSA Journal.

Common Food Products

Aluminum sulfate and related compounds can be found in a variety of foods:

Baked Goods: Many commercial baking powders and self-rising flours use sodium aluminum sulfate as a leavening acid.
Pickled Products: Traditional pickling recipes often use alum to help maintain the pickles' crisp texture.
Processed Cheeses: Certain emulsifying salts containing aluminum can be used in processed cheese products.
Candied and Crystallized Fruits: Used as a firming agent to prevent the fruits from softening.

Comparison of Aluminum-Based Food Additives


Feature	Aluminum Sulfate (E520)	Potassium Alum (E522)	Sodium Aluminum Phosphate (E541)
Primary Function	Firming, pH control, sequestrant	Firming, leavening acid	Leavening acid, emulsifying agent
Common Use	Pickles, candied fruit, cheese	Pickling, sometimes leavening in baked goods	Baked goods (double-acting baking powder), processed cheese
Regulatory Status (EU)	Permitted in specific products with restrictions	Permitted in specific products with restrictions	Permitted in specific products with restrictions
Notes	Pure compound used more for texture and pH	A traditional form of alum, also a double salt	A common ingredient in modern double-acting baking powders

Conclusion

In summary, the presence of aluminum sulfate in food is not a random or harmful occurrence, but rather a deliberate and regulated practice to achieve specific functional outcomes in food processing. As a firming agent, leavening acid, pH regulator, and emulsifier, it contributes to the quality, texture, and stability of a wide range of products, from crisp pickles to fluffy cakes. Extensive safety evaluations by regulatory bodies have affirmed its safety at the levels at which it is currently used. While dietary sources of aluminum are ubiquitous, the contribution from food additives is considered minimal and safe for the general population, making this chemical a reliable tool in modern food science.

Frequently Asked Questions

Aluminum sulfate, or alum, is added to pickled foods as a firming agent. It strengthens the pectin in the cell walls of vegetables, such as cucumbers, which helps them maintain a crisp, firm texture through the preserving process.

Yes, regulatory bodies like the FDA and EFSA have evaluated the safety of aluminum sulfate. When used within authorized levels, it is considered safe for consumption. Normal intake from food is not considered a health concern for individuals with healthy kidney function.

In baked goods, it is typically used as sodium aluminum sulfate (SAS), a leavening acid in double-acting baking powder. It reacts when exposed to the heat of the oven to help baked goods rise.

Aluminum sulfate (E520) and potassium alum (E522) are distinct compounds. While both are used in food as firming agents, potassium alum is a double sulfate salt often associated with traditional pickling and medicinal applications. Sodium aluminum sulfate is more common in modern baking powders.

Studies on the chronic effects of dietary aluminum exposure have not established a causal link to neurodegenerative diseases like Alzheimer's. Regulatory authorities have concluded that current authorized use levels are not a safety concern for the general population.

While completely avoiding aluminum is difficult due to its prevalence in the environment, you can reduce dietary intake by limiting processed foods, which are the main source of aluminum-containing additives like aluminum sulfate. Choosing products made with alternative leavening agents is one way to do this.

Yes, aluminum sulfate is vegan. It is a synthetic chemical produced by reacting aluminum hydroxide with sulfuric acid and does not contain any animal-derived substances.