Is Apple Cider Vinegar Flammable? (A Comprehensive Overview)

Is Apple Cider Vinegar Flammable?

No, apple cider vinegar is not flammable. Apple cider vinegar is composed of water (roughly 93 to 95%), acetic acid (roughly 4 to 5%), and sugars (>1%). Apple cider vinegar also contains very low amounts of other organic acids and minerals.

Although water is not flammable, acetic acid, by itself, is flammable. The main reason apple cider vinegar does not easily catch on fire is the presence of water. For a mixture of acetic acid and water to be flammable under standard conditions the amount of acetic acid would need to be above 70%.

At temperatures of up to 30 ºC, apple cider vinegar produces a small amount of vapors. Vinegar vapors are made of a mixture of water and acetic acid in their gaseous forms. The boiling points temperatures of water and vinegar are, respectively, 100 ºC and 118 ºC.

Pure acetic acid vapors in the air can become flammable at a concentration range of 4% to 16% (in volume). In the case of apple cider vinegar vapors, water vapor is also present. Water vapor reduces the contact acetic acid vapors have with the oxygen in the air.

In any combustion reaction, the more contact the fuel (acetic acid in this case) has with the oxidizing agent (oxygen gas in this case) the easier it is for the combustion to take place.

Hence, the likelihood of vinegar vapors catching on fire is far lower than pure acetic acid vapors catching on fire.

In most circumstances apple cider vinegar does not pose risks of fires or to human health. It is worth mentioning however that under some specific circumstances vinegar can lead to the formation of carbon monoxide gas (CO). Carbon monoxide is an extremely dangerous gas.

Some Thermal Properties Of Pure Acetic Acid

Pure acetic acid has a flash point (the lowest temperature at which a substance forms vapors that will ignite if subjected to an ignition source and air) of 39 ºC to 40 ºC. Such a low flash point temperature is enough data to confer acetic acid as a flammable substance.

The autoignition temperature of acetic acid is 427 ºC. This means that at this temperature acetic acid spontaneously ignites at normal pressure and without need to be subjected to any ignition source.

Some Properties of Acetic Acid Vapors

The acetic acid in the gaseous form can dimerize. In this context, dimerization is a process in which two acetic acid molecules are making strong hydrogen bonds to form a cyclic.  structure (represented in the chemical equation below).

Acetic acid in gaseous form in air is explosive at a concentration range of 4 to 16%.

What is The Acetic Acid Combustion Reaction?

When acetic acid catches on fire it is undergoing a combustion reaction. The general equation for the combustion reaction of acetic acid with oxygen gas as the oxidizer is represented below.

What is Vinegar?

Vinegar is a liquid that contains from 4% to 20% acetic acid and from 80 to 96% water and is fit for human consumption. It is derived from natural sources, and does not necessarily need human action to be produced.

As far as it is known the first mentions of vinegar being used by humans dates back to 2000 BC, for many years vinegar was considered the cheapest among fermented food products.

Vinegar has pretty much no nutritional value, but it is very effective to preserve food given its acid content being a good microorganisms inhibitor (at the same time the acidic of vinegar is not so high as to deteriorate food).

Vinegar can be obtained from a series of different agricultural raw materials. The main requirement is possessing an edible carbohydrate (sugar) source. Most common raw materials used to produce vinegar include apple, berries, coconut, grapes, malta, mango, kaki, rice and even honey. 

Despite the diversity of raw materials that can be used to produce vinegar, the most common source is produced directly from alcohol (ethanol, CH3CH2OH). Vinegar produced this way is denominated “white” vinegar, and it is widely used in the food industry dressings and sauces.

What is The History of the Consumption of Vinegar?

The oldest known mention of vinegar consumption dates to around 5000 BC, when Babylonians used it as a condiment and as a preservative.By that time vinegar was the strongest known acid to man (acetic acid is extremely weak in acidity compared to sulfuric acid).

This acidic characteristic of vinegar was and is until today extremely to preserve food. As the acidic nature of vinegar was helpful in combating the action of microorganisms.

There are records of vinegar being used to help heal wounds and as an antiseptic by 2000 BC. Furthermore, vinegar was also used to help treat wounds during World War I.

During the production of fermented beverages, such as wine and beer, vinegar became a by-product. Some wines were partially converted into vinegar in ancient Roma. And, the name ‘vinegar’ originated from the French term ”vin aigre” which translates to “sour wine”.

How is Vinegar Made?

Vinegar is produced from raw materials that contain starch and sugars The raw materials can be from an array of different origins. The process for obtaining vinegar from these raw materials is two subsequent fermentation processes, which can be performed in different approaches.

The two-step fermentation process consists in an alcoholic fermentation (transformation of sugars into ethanol) followed by acetification (oxidation of the ethanol into acetic acid, also known as ethanoic acid).

Both these chemical transformations (alcoholic fermentation and acetification) are performed by microorganisms. Yeasts convert sugar (different carbohydrates) into alcohol (ethanol, more specifically). Acetic acid bacteria promotes the oxidation of ethanol into acetic acid.

For the second step (the oxidation of ethanol into acetic acid), there are two main approaches to produce vinegar in large scales:

The traditional approach is by static surface culture, in which the acetic acid bacteria is placed at the interface between the liquid and the air.

By submerging the culture with a continuous air flow by means of bioreactors. This way the oxidation of ethanol into acetic acid takes place in air bubbles interface with the liquid. With a higher surface are for the biotransformation to occur the formation of acetic acid takes place at a faster rate than the above approach.

Overall the traditional approach furnishes higher-quality vinegars, given the higher chemical complexity of the side products of the oxidation, which confers a more complex organoleptic quality.

What is the Role of Bacteria in the Production of Vinegar?

Acetic acid bacteria is essential for the production of any  type of vinegar. They can be Gram-negative or Gram-variable (those that cannot be classified as either positive or negative). 

They have an aerobic respiratory metabolism, usually requiring oxygen to survive but they can survive in the absence of oxygen. In fact, that is why they can act on the transformation of ethanol into acetic acid (this process is anaerobic).

The main bacteria genera that is involved with the formation of vinegar are Acetobacter, Gluconacetobacter, and Komagataeibacter.

Additionally, acetic acid bacteria also can be involved in the fermentation of cocoa and coffee which happen without the need of human made processes.

How Does Fermentation of Apple Juice Work?

The proper bacteria consumes the nutrients and sugars from apple juice and added sugars to form ethanol (CH3CH2OH). Ethanol is subsequently oxidized to acetic acid (CH3CO2H).

How Is Apple Cider Vinegar Made?

Apple cider vinegar is ultimately obtained by the fermentation of a mixture of apple juice and sugars. The fermentation is performed by bacteria (naturally occurring on the apple juice or added in the production process) and yeast (added during the process).

Acetic acid can be formed without the action of humans under favorable natural conditions.

Conclusion

Apple cider vinegar does not pose any immediate danger of fires or explosion, nor does any of the other types of vinegar. The main component of vinegar apart from water, acetic acid, is in fact highly flammable and combustible when it is isolated from water, but such an isolation is extremely unlikely to happen. Nonetheless, there are specific circumstances that require caution when dealing with vinegar, some of these have been mentioned in this article.

Frequently Asked Questions (FAQ): Is Apple Cider Vinegar Flammable?

Does vinegar fuel fire?

That depends on the fire and what is the cause of it. Most common fires will not be fueled by vinegar to any significant extent. That is because vinegar is mostly water.

Can vinegar cause explosions?

If vinegar is mixed with a basic chemical such as baking soda (sodium bicarbonate, NaHCO3), carbon dioxide gas is produced at a fast rate, which in turn can lead to a gas build up if this process takes place in a very confined space. Nonetheless, if an explosion would occur this way, it would not be a very dangerous one.

Is vinegar and baking soda flammable?

Neither vinegar or baking soda are flammable or combustible. The acetic acid present in vinegar is a highly flammable substance however.

What happens to vinegar when it gets hot?

If there is nothing else in contact with vinegar and its vapors, the only thing that happens with vinegar when heated is the faster evaporation of the water and the acetic acid. If other materials are near the heating vinegar that’s another story. Acetic acid vapors can react with some materials including metals causing corrosion. Under some specific circumstances heating vinegar can lead to the formation of dangerous gases such as carbon monoxide.

What happens when you mix vinegar and baking soda?

Vinegar contains a weak acid, acetic acid (CH3COOH), baking soda is made of a weak base, sodium bicarbonate (NaHCO3). When they are mixed with each other an acid-base reaction takes place producing sodium acetate (NaCOOCH3), carbon dioxide (CO2) and water. Sodium bicarbonate is a white solid and it is a stronger base than sodium bicarbonate. Water can be seen as a very weak acid (so weak, that by itself it is considered neutral).

Is vinegar corrosive to metal?

Yes, as an acidic substance, acetic acid is corrosive to metal as is pretty much any acid. The corrosion process is relatively slow however.

References

M.C. Garcia-Parrilla, M.J. Torija, A. Mas, A.B. Cerezo, A.M. Troncoso, Chapter 25 – Vinegars and Other Fermented Condiments, Editor(s): Juana Frias, Cristina Martinez-Villaluenga, Elena Peñas, Fermented Foods in Health and Disease Prevention, Academic Press, 2017, Pages 577-591, ISBN 9780128023099, https://doi.org/10.1016/B978-0-12-802309-9.00025-X

A. Mas, A.M. Troncoso, M.C. García-Parrilla, M.J. Torija, Vinegar, Editor(s): Benjamin Caballero, Paul M. Finglas, Fidel Toldrá, Encyclopedia of Food and Health, Academic Press, 2016, Pages 418-423, ISBN 9780123849533,  https://doi.org/10.1016/B978-0-12-384947-2.00726-1

https://fdc.nal.usda.gov/fdc-app.html#/food-details/173469/nutrients

Ulbricht CE, ed. (2010). “Apple Cider Vinegar”. Natural Standard Herb & Supplement Guide: An Evidence-Based Reference (1st ed.). Elsevier. p. 59.

Acetic acid dimerization study:

Socha, O.; Dračínský, M. Dimerization of Acetic Acid in the Gas Phase—NMR Experiments and Quantum-Chemical Calculations. Molecules 2020, 25, 2150. https://doi.org/10.3390/molecules25092150 

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