Types of Vinegar

Apple Cider vinegar, Balsamic vinegar, Red Wine vinegar and Distilled White vinegar. The main difference between them is primarily associated with the raw materials, which are used in the alcoholic fermentation.

• Apple Cider vinegar is primarily made from fermented juice of apples.
• Balsamic vinegar is made from the white Trebbiano grape.
• Red Wine vinegar is made from low quality wine that has been subjected to aerobic oxidation. Red wine can be converted to vinegar.
• Distilled White vinegar is made from distilled ethanol, which may be fermentation ethanol.

These are just some of the many different types of vinegar developed using the same principles as those used in the early 1900’s when vinegar fermentation became popular.

Fermentation Process

 The chemical process through which wine or fruit juice becomes vinegar involves the partial oxidation of ethyl alcohol that results in the formation of acetaldehyde, which is then converted into acetic acid (www.encyclopedia.com/topic/vinegar). The chemical reaction is as follows:

CH ₃ CH ₂ OH=2HCH ₃ CHO=CH ₃ COOH

Acetic acid bacteria are in the family Acetobacteraceae and Gluconobacter (Buchanan and Gibbons 1974). Acetic acid bacteria are Gram-negative, ellipsoidal to rod-shaped cells that have a need for aerobic metabolism as the terminal electron acceptor (Gonzalez et al., 2004).

The formation of vinegar starts with alcohol, with added sour ferment, all diluted with water and then exposed to the atmosphere. The vinegar becomes stronger the more alcohol that is present. The alcohol is the material in the vinegar mixture that the acetic acid is derived. The highest aim for the producer in the manufacture of vinegar is ultimately the conversion of alcohol into acetic acid with the least loss of alcohol possible (Francis & Croft, 1842).

Wine vinegar is prepared from wine and together with acetic acid contains all other constituents of wine such as tartaric acid. Cider vinegar is prepared from the fermented juice of apples and besides acetic acid contains malic acid which give apples their sour taste and is used in the food industry in fruit flavoured confectionary products. Malt vinegar is prepared from fermented extract of malt and as well as acetic acid contains nearly all the constituents of beer such as phosphates and extractive substances. Many of the substances which are used in the production of vinegar such as wine, fruit and malt contain the ingredients which ordinarily give rise to the formation of vinegar and they can be converted into vinegar sometimes without the addition of any acid ferment (Francis & Croft, 1842).

Production Methods of Vinegar

Production of vinegar may vary from traditional methods employing wood barrels (Orleans Process) and generator fermentation to submerged fermentation in acetators (Fringes process)

Orleans Process

The earliest vinegar manufacturing method, which was originated in France, was known as the ‘Orleans process’ or also known as the ‘slow process’.
    

  Wooden barrels are used and are filled with alcohol fermenting liquid to almost three quarters full. Holes are drilled into the ends of the barrel a few inches above the liquid level in order to allow air circulation. The holes are left open and netting or screens are placed over the holes in order to prevent insects from getting into the barrels. Fresh vinegar is added to the barrel to acidify the liquid to the point of optimum growth necessary for the vinegar bacteria. The vinegar bacteria settle down into the liquid and a slimy layer develops on the top of the liquid.

 This is a slow process because the bacteria come in contact with the air and the substrate only at the surface. The air is supplied through the holes in the barrel. The fermented liquid is allowed to sit for several months with free access to air. Once the alcohol fermenting liquid becomes acetified or is converted to vinegar through activity of organisms growing on or close to the surface of the liquid, a proportion of the vinegar may then be drawn off and replaced with alcohol fermenting liquid and the process is restarted. The acetic acid may become oxidised if the alcohol sources are not constantly added to the vinegar.

 Today, only a very small proportion of the world’s vinegar is produced by this Orleans method, although it is reported to be the best method to produce the finest quality vinegars. 

 Generator fermentation

As a result of the Orleans process being so slow and time consuming, other methods have been adapted in order to try and speed up the process. The German method is one such way, known as the ‘generator process’ or also known as the ‘quick process’.

In this process  the alcoholic solution to be acetified is allowed to trickle down through a tall tank or column packed with porous solid material on whose surface Acetobacter bacteria are permitted to grow. Suitable solids, which are frequently used, are wood shavings or corncobs. This column in the vinegar industry is known as a generator.

http://www.realmagick.com/vinegar-production/

The bacteria grow upon the surface of the wood shavings and form a thick slime coating around the non-compacting material such as beech wood shavings.  The air enters the generator at the bottom and moves upwards towards the top. The acetic acid bacteria use the air in order to oxidise the alcohol. A limited air supply means limited acetic acid production while an overabundant air supply creates over production and higher generator temperatures.

In order to achieve efficient vinegar production it is necessary to provide an ample supply of oxygen to the liquid substrate without passing air though the substrate at a rate which will cause excessive losses of alcohol or acetic acid by evaporation. The generator needs to be carefully monitored to present over oxidation or unacceptable high temperatures in order to avoid damaging the bacteria. 

 

Vinegar Production

Submerged technology (Tim)

Submerged acetification has been used in baker’s yeast since the start of the 19^th century, however its potential has only been recently recognised by the vinegar industry.  The principle behind this process is that of control of the acetic acid bacteria, the bacteria can be help in an oxygen deprived atmospheres for varying amounts of time, once this process has ceased and oxygen added to the fermentation process again the rate of acetification was dependant on the length of time the bacteria had been deprived of oxygen the longer it was deprived the quicker the rate of acetification.


 The most successful method of submerged acetification has been the Acetator, which was developed by Henrich Frings

Technological advancements have allowed for new and alternative methods then the traditional methods mentioned above for the fermentation of vinegar. Most modern vinegar plants now work with Frings technology (www.fringsamerica.com). 

This technology works on the basis that the acetobacter (bacteria responsible for converting alcohol to acetic acid) is kept in a floating state inside the alcoholic mash with the aid of an aeration turbine. This technology produces high standards as automation is possible and high acetic acid levels can be reached, a constant struggle within traditional methods

Acetic acid bacteria used in vinegar fermentation (taken from google images)

Vinegar Quality

The quality of food can be evaluated by taking into account different perspectives such as nutritional value, food safety and sensory properties. In the case of vinegar, it is usually determined by sensory properties as it may modify the overall appreciation of a meal and so it is the best tool to define the quality of the vinegar.

Overall quality of vinegars can be determined by the substrate used, the acetification conditions and ageing. For wine vinegar, the type of wine used for acetification can influence the fermentation process, for example, a wine with low residual sugar should be used to allow for adequate bacterial growth. For vinegars to be of high-quality, they must be aged in wooden barrels. The organoleptic properties that develop during ageing make the finished product highly valued (Tesfaye et al., 2003).
 

The quality of vinegar is firstly directly dependent on the quality of the raw material used. Aging plays an important role in the improvement of vinegar quality, especially for those vinegars made with a submerged culture system.