Citric Acid and Aspergillus Niger ("Black Mold"): The Science Behind a Common Ingredient

Citric acid is one of the most widely used food additives and cleaning agents in the world. Found in everything from soft drinks to dishwasher detergent, this naturally occurring compound is prized for its tart flavor, preservative properties, and ability to break down mineral deposits. But what many consumers don’t realize is that most commercially produced citric acid isn’t derived from citrus fruits—it’s made using Aspergillus niger (aka "Black Mold"), a type of mold.

If you’re wary of consuming citric acid because of its fungal origins, you may be surprised to learn that many other common food and pharmaceutical products rely on the same microbial fermentation process—including the enzymes used in cheesemaking. In this article, we’ll explore how citric acid is produced, examine other products derived from Aspergillus niger, and discuss why those avoiding citric acid for this reason may also need to rethink their stance on cheese.

Milliard Citric Acid

How Citric Acid Is Produced Using Aspergillus Niger

The History of Citric Acid Fermentation

Citric acid was first isolated from lemon juice in 1784 by chemist Carl Wilhelm Scheele. For over a century, it was extracted from citrus fruits, but this method was expensive and inefficient. In 1917, American food chemist James Currie discovered that Aspergillus niger could produce citric acid when grown on sugar-rich substrates. This discovery revolutionized citric acid production, making it vastly more cost-effective and scalable.

The Industrial Production Process

Today, citric acid is primarily produced through a fermentation process that relies on Aspergillus niger, a harmless black mold that naturally secretes citric acid when fed a sugar-based substrate. Here’s how it works:

  1. Inoculation – A culture of Aspergillus niger is introduced into large fermentation tanks filled with a sugar-rich solution, often derived from corn syrup, molasses, or sugar beets.

  2. Fermentation – Over several days, the mold metabolizes the sugars and secretes citric acid as a metabolic byproduct.

  3. Purification – The resulting solution is filtered to remove fungal biomass, and citric acid is isolated through precipitation and crystallization.

  4. Final Processing – The purified citric acid is dried and processed into either powder or liquid form for use in various industries.

This fermentation method has completely replaced fruit-derived citric acid production due to its efficiency, cost-effectiveness, and sustainability.

Other Products Derived from Aspergillus Niger Fermentation

While citric acid is the most well-known product derived from Aspergillus niger, it’s far from the only one. This mold is an essential player in the biotechnology and food industries, producing a range of valuable compounds, including:

1. Gluconic Acid

  • Used as a food additive and in cleaning products.

  • Helps regulate acidity in beverages and prevents crystallization in honey.

  • Commonly found in toothpaste, pharmaceuticals, and dairy products.

2. Enzymes Used in Food Processing

Aspergillus niger is also a key producer of enzymes that help break down food components for easier processing and digestion:

  • Pectinase – Used in fruit juice production to improve clarity and yield.

  • Amylase – Breaks down starch into sugars, used in baking and brewing.

  • Cellulase – Helps break down plant fibers in food and animal feed.

  • Lactase – Used to create lactose-free dairy products.

3. Chymosin: The Cheese-Making Enzyme

One of the most surprising products derived from microbial fermentation is chymosin, the enzyme used to coagulate milk in cheesemaking. Traditionally, chymosin was extracted from the stomachs of young calves, but today, it is predominantly produced through genetically modified Aspergillus niger and other microbial hosts.

How Chymosin Is Made Using Aspergillus Niger:

  1. Scientists insert the chymosin-producing gene from calves into Aspergillus niger or other microbes.

  2. The fungus is then cultivated in fermentation tanks, where it produces chymosin.

  3. The enzyme is extracted, purified, and used in cheesemaking.

This microbial-derived chymosin is considered identical to the animal version, making it widely accepted for vegetarian cheese production. However, it also means that those avoiding citric acid due to its fungal origins would need to avoid most modern cheeses as well.

Should You Avoid Citric Acid Due to Aspergillus Niger?

There is a growing trend of consumers seeking to avoid citric acid due to concerns over its microbial production. However, this perspective may overlook some key facts:

  • Aspergillus niger is completely removed from the final product. The fermentation process results in pure citric acid, with no remaining fungal material.

  • This method is used for many everyday food products, including cheese, fruit juices, and dairy alternatives.

  • The same fermentation technology is used in pharmaceuticals, including enzyme supplements and antibiotics.

If you’re avoiding citric acid because of its fungal origin, consistency would require avoiding many processed foods, including:

  • Most modern cheeses

  • Fruit juices and plant-based dairy alternatives

  • Some baked goods and soft drinks

  • Certain supplements and medications

Understanding the Bigger Picture

Citric acid, one of the most common ingredients in food and cleaning products, is produced through an efficient and sustainable fermentation process using Aspergillus niger. While some consumers may find the idea of mold-derived ingredients unappealing, this same biotechnology is responsible for producing essential enzymes like chymosin in cheese, lactase in lactose-free dairy, and many other food additives.

Avoiding citric acid solely because of its fungal origins means avoiding a vast array of foods and pharmaceuticals that use similar fermentation techniques. Rather than focusing on its production method, it’s essential to recognize citric acid’s safety, effectiveness, and the broader role of microbial fermentation in modern food science.

For those who prioritize clean, minimal ingredients, choosing products that are free from unnecessary additives, synthetic preservatives, and plastics—like Minimalist Shine’s dishwashing tablets—is a great way to ensure a healthier lifestyle without unnecessary fears surrounding safe, naturally derived compounds.

Back to blog