Vinagre

Vinegar is a solution of 4 to 15% acetic acid with flavouring and fragrance agents. Acetic acid is an organic acid with a typical strong odour. According to the Dutch Commodities Act, the name ‘vinegar’ may be used only for products that contain 4% or more acetic acid, otherwise the product must be labelled Posca.

Vinegar is used in the preparation of various sauces, such as mayonnaise and mustard, and to pickle vegetables. Pickling vinegar (distilled white vinegar) is colourless and has a higher percentage of acetic acid. The vinegar softens fibrous structures and breaks down the fat, making products easier to digest.

The pH level of vinegar is between 2 and 3.5, depending on the concentration of the acetic acid. As a result, vinegar can be used to preserve products.

There are many types of vinegar, because basically all products that contain sugars can be used as a basis for vinegar. Besides acetic these vinegars also contain ingredients of the raw material. Some common examples are:

• Apple vinegar
• Wine vinegar (red or white)
• Balsamic vinegar: concentrated wine vinegar (matured in wooden barrels for at least several years)
• Rice vinegar (red, black or white)
• Herbal vinegar: vinegar with added herbs
• Malt vinegar: starch converted into maltose.

There is also a natural vinegar available in the Netherlands, recognizable by the letter N on its bottle cap. Natural vinegar is made from sugar and water, so it has a neutral taste and contains no minerals. When this vinegar is kept in a dark place, it can last up to two years without spoiling.

Vinegar production

All products that contain sugars are used as a basis for vinegar. The sugars are converted into alcohol by using yeast. Next, the alcohol is converted, with the presence of oxygen, to acetic acid by the acetic acid bacterium Acetobacter. This conversion consists of two steps. During the first step, ethanol is converted into acetaldehyde (ethanal), after which the acetaldehyde is converted into acetic acid.

Formation of acetic acid

Below, the formation of acetic acid by different methods is discussed.

Wooden barrel

The alcohol product is placed in a wooden barrel with several air holes. To keep insects from entering the barrel, protective screens are placed over the air holes. The wooden barrel still contains 15% of the vinegar from the previous production run, so the same bacteria culture can be used again. Also, the acetic acid bacterium is already naturally present in the air. The barrels are left to rest for a few months at a steady temperature of 29°C, until the desired acidic level of the acetic acid has been reached.

Filled oak barrel

A tall oak barrel is filled with beech wood shavings, charcoal or grape pulp. The alcohol product is poured into the barrel from the top, after which it slowly seeps through the filling. With an air compressor air is blown through the perforated bottom and holes in the sides of the barrel, to the product. After a number of days or weeks, the vinegar will reach the bottom of the barrel with such a high acetic acid content that it has to be diluted with water to an acetic acid content of 5 to 6%. The vinegar is then passed to a storage tank.

Acetator (vinegar fermenter)

On the bottom of a large generator, also called acetator, there is a bar grating with beech wood shavings, which are a natural source of the acetic acid bacteria. This generator is filled with an alcoholic product. By using the centrifugal pumps attached to the bottom of the acetator, air bubbles are pumped into the alcohol product. As a result, the acetic acid bacteria get enough oxygen and the alcohol product is constantly pumped past the wood shavings. This process continues until all of the alcohol has been converted to acetic acid. This takes places at a constant temperature of 30°C. The resulting vinegar is then transferred into large plastic barrels to rest and mature.

Natural Vinegar

Natural vinegar is also produced with an acetator. In this case, the concentrated alcohol (96%) is mixed with some of the crude vinegar from a previous production and water in a mixing tank. This results in an alcohol solution of 40%, which is then diluted down further to 12%, in another tank. In addition, nutrients for the acetic acid bacteria are added. The whole mixture is then pumped to the acetator.

This method also involves the acetic acid bacteria getting enough oxygen through the supply of air, and continues movement of the mixture. The temperature is maintained at a steady 28°C. At the end of the process, approximately 12% acetic acid is formed, leaving an opaque brown blend, the so-called sprit vinegar. Some of the sprit vinegar is re-used in the mixing tank.

Filtering

After the vinegar has been produced by using one of the methods mentioned above, it will be filtered. With stainless steel plates, the vinegar is pressed through paper filters to remove sediment, which usually makes up about 3% of the product.

During the production of natural vinegar, a racking tank is used. The sedimentation process is accelerated by adding a flocculant, like bentonite. Next, the top layer of the mixture is drained until 30 cm (from the bottom of the tank) of vinegar is left, after which the final insoluble particles are removed through means of ultrafiltration. The resulting bulk or vinegar is sold as a bulk or diluted to an acetic acid content of 4%.

Distilling

Optionally, the vinegar can be distilled. To achieve this, the vinegar is brought to boiling temperature. The vapour that is released during this process is collected in a condenser, after which the condensate is ready to be bottled.

Pasteurization and bottling

The filtered product is usually also pasteurized. The final step involves bottling the vinegar in glass or plastic. The final product can be stored outside the refrigerator.

Food Safety & Hygienic Design

Alcohol is a natural preservative. Alcohol is, from a certain percentage, a toxin that prevents natural growth of many microorganisms. The few microorganisms which may be able to grow, are not pathogenic and acidify the product. The process of microbial acidification is a non-sensitive process, provided that this process is started with a sufficient number of Acetobacterium.

The final product is microbially stable. The minimum alcohol percentage of 4% works as a preservative. Besides being used as seasoning, it can also be used as a natural preservative.

The production equipment and machinery must be of a GMP-class. This means that the machinery and equipment must be visibly clean before use. In case that the machinery cannot be emptied fully (and set aside clean and dry), the machinery has to be thoroughly cleaned and disinfected before the production process can start again. Cleanable to a microbial level (hygienic design) is not necessarily required for this process. A light microbial contamination should not be a problem, provided that the Acetobacter-culture catches on fast enough. The preserving effect of acetic acid can automatically preserve the equipment and machinery. Frequent cleaning is not always necessary, and if a good product is produced from hard to clean machine or piece of equipment, often also not desirable.

However, what is important, is the corrosion resistance of the materials used. Even the more resistant AISI 316 can be insufficient at higher temperatures. AISI 304 is often not suitable.