⚠️ Critical Finding: The European Food Safety Authority concluded that actual consumer exposure to E521 is “most probably near zero” because uses are limited to only two food categories with further restrictions, and products containing it are increasingly rare.

How E521 Works in Baking

E521’s primary function is as a slow-acting leavening agent in double-acting baking powder.

Most commercial baking powders contain two leavening acids:

– Fast-acting acid (Monocalcium Phosphate): Reacts immediately when wet, releasing carbon dioxide
– Slow-acting acid (Sodium Aluminum Sulfate): Remains dormant until heated

When you mix wet ingredients with baking powder, the fast-acting acid creates immediate gas, causing the batter to rise slightly. During baking, heat activates the slow-acting acid (E521), which reacts with baking soda to release additional carbon dioxide, causing further rising in the oven.

This two-stage reaction creates better texture and rise in baked goods compared to single-acting baking powders.

Why Do Food Companies Use E521?

E521 serves a specific and important function in baking chemistry.

Its slow reaction with baking soda (only at heat) makes it ideal for commercial baking, where dough may sit for extended periods before baking. E521 doesn’t cause premature rising, ensuring uniform texture and proper rise in the oven.

Additionally, E521 acts as an acidity regulator and bleaching agent in certain applications, improving product stability and appearance.

However, due to declining use and availability of aluminum-free alternatives, manufacturers are increasingly switching to other leavening systems. The Mintel Global New Products Database shows fewer products containing E521 over time, especially following February 2014 legislative changes.

Is It Safe?

Regulatory authorities consider E521 safe at approved use levels—but with important caveats.

The FDA classifies it as “Generally Recognized As Safe” (GRAS) when used per good manufacturing practices. The EFSA’s 2018 comprehensive safety re-evaluation concluded that aluminum sulphates (E520-523) “are of no safety concern in the current authorised uses and use levels.”

However, approval comes with significant restrictions:

– Uses authorized in ONLY TWO food categories
– Additional restrictions exist beyond those two categories
– Real-world consumer exposure: “Most probably near zero”
– Industry no longer submitting use data to EFSA
– Fewer products containing E521 over time

The Aluminum Question

The primary health concern with E521 is its aluminum content.

Alums have been controversial due to historical associations with Alzheimer’s disease. However, important points apply:

– Aluminum from E521 has LOW bioavailability (limited absorption)
– EFSA found NO evidence of carcinogenicity or genetic damage
– EFSA found NO adverse reproductive or developmental effects
– EFSA found NO evidence supporting Alzheimer’s link at food additive levels
– Actual exposure is negligible

The aluminum compounds have low acute toxicity and limited intestinal absorption. At the trace amounts found in baked goods, E521 poses no identified health risk according to regulatory authorities.

EFSA’s 2018 Safety Re-evaluation

The EFSA’s comprehensive 2018 assessment provides crucial context.

Key findings:

– Aluminum sulphates (E520-523) pose no safety concern at current use levels
– No genotoxicity (genetic damage)
– No carcinogenicity (cancer)
– No reproductive/developmental toxicity
– Low bioavailability of aluminum
– Actual human exposure “most probably near zero”

EFSA emphasized that these additives are “only authorised in specific products which consumption is not captured in the dietary surveys,” meaning they’re so niche that standard health studies don’t even measure exposure to them.

Declining Use and Regulatory Trend

E521’s use has declined significantly since 2014.

Following legislative changes in February 2014 that restricted aluminum-containing additives, the Mintel Global New Products Database shows a consistent decrease in products containing E521. Additionally, industry no longer submits use level data to EFSA, suggesting manufacturers have largely moved to aluminum-free alternatives.

This trend reflects both regulatory pressure to minimize aluminum additives and the availability of effective non-aluminum leavening systems.

Comparison with Related Additives

E521 is one of four aluminum-containing additives:

– E520: Sodium aluminum sulfate
– E521: Sodium aluminum sulfate (this product)
– E522: Potassium aluminum sulfate
– E523: Ammonium aluminum sulfate

Of these, E521 (sodium-based) was historically the most common in baking powders, though all four are now severely restricted.

JECFA Status

E521 has an interesting regulatory history with JECFA.

No Acceptable Daily Intake (ADI) was allocated by JECFA since 1978. This is not a safety concern—rather, it reflects historical approval practices. The lack of specific ADI doesn’t indicate danger; rather, it indicates the substance was approved before modern ADI-setting procedures became standard.

Manufacturing and Chemistry

E521 is synthetically produced through chemical reaction.

Sodium sulfate and aluminum sulfate are combined to create the double sulfate compound. The anhydrous form is slowly soluble in water, while the dodecahydrate form (more common) is readily soluble.

It’s entirely synthetic with no natural source.

Baking Properties and Effects

E521 imparts specific characteristics to baked goods.

– Creates light milk chocolate color in cake crumb
– Has a very slow reaction rate (only at heat)
– Slight metallic or astringent aftertaste possible
– Neutralizing value of 104 (ratio of baking soda needed for complete reaction)
– Strengthens cake structure but may slightly weaken crumb texture

Vegan, Vegetarian, and Allergen Status

E521 is suitable for:

– Vegan diets ✓
– Vegetarian diets ✓
– Gluten-free diets ✓

Sodium aluminum sulfate is a chemical compound with no animal products or byproducts involved in its production.

The Bottom Line

E521 (sodium aluminum sulfate) is an aluminum-containing food additive used as a slow-acting leavening agent in baking powders and baked goods.

Regulatory authorities approve it as safe at current use levels, with EFSA specifically finding “no safety concern in current authorised uses and use levels.”

However, uses are severely restricted—authorized in only two food categories with further limitations. Real consumer exposure is negligible.

Most notably, its use has declined significantly since 2014, reflecting both regulatory tightening and industry preference for aluminum-free alternatives.

Many consumers eating modern commercial baked goods may never encounter E521, as manufacturers increasingly use alternative leavening systems.

As always, food labels must declare E521 when used, enabling informed consumer choice—though finding products containing it now requires effort, as it’s increasingly rare in modern baking.