Is Citric Acid Flammable?

In this article, we will discuss the following question: “Is citric acid flammable?”, and other important topics on the subject.

Is Citric Acid Flammable?

Yes, citric acid can burn under certain conditions, particularly in its powdered form, where there is a serious risk of explosion. It is an organic compound, present mainly in citrus fruits (such as oranges and lemons). An attempt to ignite powdered or concentrated citric acid can be very dangerous.

What is citric acid?

Citric acid is an organic compound present in most living things, it’s considered a weak acid. It occurs naturally mainly in citrus fruits such as lemon and orange, where its main association comes from.

Citric acid is also important for industries, it serves as an ecological solvent, which performs the cleaning function without harming the environment in the process. 

In addition, it is very important for the food industry, as an acidulant, preservative, and flavoring agent, giving citrus characteristic flavors to many foods.

Citric acid can be found naturally dissolved in citrus fruit juices and some kinds of vinegar. Lemons can have up to 8% of their dry weight (dried fruit) from citric acid alone. 

The Penicillium genus of fungi (where we find the fungus responsible for penicillin) is also capable of producing citric acid from sugar fermentation, but since World War II, this method has not been widely used industrially. 

Aspergillus niger, another famous fungus, also known as “black mold” was another natural alternative to produce citric acid naturally, but this alternative was practically abandoned.

Nowadays, the main way to obtain citric acid is through aconitic calcium salts, obtained from aconitic acid, the main acid found in sugarcane. 

A curiosity about this process is that it’s considered a reverse reaction of the Krebs cycle. While living beings use citric acid to utilize sugar, in industrial processes, they use sugar to produce citric acid.

What is the Krebs Cycle?

Krebs Cycle, or Citric Acid Cycle, is a chain of reactions from citric acid that occurs inside the cell of aerobic organisms (which breathe oxygen) in an organelle called mitochondria. 

This chain of reactions is primarily responsible for obtaining energy from food through glucose.

Citric Acid uses

Citric acid has numerous applications.

It can be used as an ecological cleaning agent since it does not generate harmful residues in the environment. In the food industry, we have its main uses. 

It’s used as an acidulant in beverages, representing 50% of the market, but it can also be used as a preservative, and emulsifying agent in ice cream and charcuterie pasta, in addition to being one of the most popular flavorings that exist.

Outside the food industry, it is used for the production of detergents and solvents, as well as cosmetics and products for the chemical and pharmaceutical industry.

Its mixture with baking soda is famous for fizzy drinks and antacid medications. It can be found in powdered form in pharmacies and markets as “sour salt”. The higher the purity of the citric acid salt, the greater the risk of flammability.

Citric acid risks

Despite being considered a weak acid, citric acid, mostly pure, can present some health risks. Its inhalation can cause shortness of breath, sore throat, and cough. 

Prolonged consumption can cause tooth enamel loss. Prolonged skin exposure can cause redness and pain. And its combustion can generate an explosion, but only under certain conditions.

Citric Acid properties

The melting temperature of citric acid is 156°C (313°F) and its boiling temperature is 310°C (590°F), although it degrades from 175°C (347°F).

Widely used for its antioxidant properties, it is an excellent preservative and acidulant. It also serves as a blood anticoagulant, by chelating blood calcium, and preventing clotting.

Its most commonly found industrial form is through odorless, translucent (depending on the degree of purity), and colorless crystals with an acidic flavor, denser than water. 

Its molecular formula is C6H8O7. From this acid, it is possible to extract a class of salts known as citrates, where Trisodium Citrate and Triethyl Citrate are the two most known.

On citrate, in addition to being an anticoagulant (chelating) agent for the blood, it also serves to transport various metal ions in food supplements. 

It is very common in vitamin supplements that the salt used in various metals is Citrate because it is biologically available. Its nutritional value is 247kcal per 100g.

Citrates have important buffering properties (they serve as a buffer in solutions) used mainly in the pharmaceutical industry. In the cosmetics industry, it is an important acidulant for gels, creams, and liquids, without causing damage to the skin. 

It can be added to shampoos and soaps to increase their cleaning and wax removal and, hair coloring effectiveness. They can also be used for water treatment, and for cleaning limescale accumulation through acid and base reaction. 

And finally, when mixed with soaps and fabric softeners, it forms more foam and increases the softening function of the product.

It can be obtained in its anhydrous form (no water) or monohydrate (low water content). The anhydrous form is obtained by extraction in hot water, while the monohydrate form is obtained in cold water.

Although, it can be converted to an anhydrous form at 78°C (172.4°F). From 175°C (347°F) it begins to decompose into carbon dioxide and other carbon oxides.

It is capable of corroding Copper, Zinc, Aluminum, and their alloys, but the effect is usually weak and takes place in the long term, and can be seen in pans of these materials that have cooked citrus foods over time. 

But what is combustion?

Combustion is a chemical reaction between a source of fuel and oxygen in the presence of heat. 

The fuel must be an organic compound that can liberate heat when the reactions take place. This happens because the fuel molecules are full of energy, and a lot of them are released in the form of heat and light.

When something burns, a source of carbons (C) and hydrogens (H) is consumed along with oxygen (O) to give birth to carbon dioxide (CO2), water (H2O), and the energy we mentioned.

No atoms are lost during combustions, they simply rearrange into simpler molecules. Normally, simple and stable molecules have low energy, which means that they lost energy after was formed.

This happens because, in chemistry, lower states of energy are usually a synonym for stability.

Heat and light are precisely this “lost” energy.

Fire is the visual part of complex chemical reactions that happens every time a source of fuel has the right conditions to do so. We can say that fuels are always “waiting” to burn.

Citric acid flammability

Citric acid presents a serious risk of flammability and explosion in its powder form. 

The risk of burning when exposed to flames or heat is low, as it melts and decomposes into carbon oxides, however, if combustion occurs, its powder form is capable of generating explosion and fire, according to the Clear View Enterprise technical report

Its explosion generates carbon oxides (CO, CO2, etc.) and acrid (burning) smoke, which can irritate the skin and eyes.

Its flame can be extinguished by any traditional flame extinguishing means such as Water, Water Fog, Foam, Carbon Dioxide, and Dry chemicals.

Liquid forms of citric acid are not particularly flammable, but they can ignite after some heating. The more concentrated a citric acid solution is, the more flammable it is as well.


Citric Acid is considered flammable in its powder and concentrated form. But even then, direct sources of heat and/ or flames are required, so citric acid is not a major fire hazard. At the same time, it can ignite if the right conditions are provided.

Frequently Asked Questions (FAQS): Is Citric Acid Flammable?

Is citric acid a strong acid?

It is relatively considered a weak acid. Its pH is between 3 and 6. Strong acids have a pH between 0 and 1.

pH is a measure of the quantity of hydrogen that can become ionizable in an aqueous solution.

is citric acid vitamin c?

No. Citric acid is a compound and vitamin C (ascorbic acid) is a totally different one. Vitamin C is something that is beneficial for our health in certain quantities. Citric Acid can be eaten and digested by us, but it’s not an important nutrient.

is citric acid soluble in water?

Yes, it has good water solubility. This is because it’s a carboxylic acid whose carbon chain is not very big, only 6 carbons in length.

The carboxylic ligand enhances the water solubility greatly, due to the solvation of that molecule area with water.


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