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Vinegar : Preparation and its types

T(caps)he word vinegar has been derived from French word ‘vin’ meaning sour and ‘aiger’ meaning wine. The vinegar contains acetic acid and Latin word ‘acetum’ also means sour wine. These French and Latin words indicate first vinegar was probably a result of spoiled wine and its production is as old as wine. Thus vinegar is oldest known fermented liquid product which is obtained from oxidative fermentation of ethanol solution by acetic acid bacteria. According to Cruess (1958) vinegar is a condiment made from various sugary and starchy materials by alcoholic and subsequent acetic fermentation. According to Codex Alimentarius Commission “ Vinegar is a liquid fit for human consumption, produced from a suitable raw material of agricultural origin, containing starch, sugars or starch and sugars by the process of double fermentation, alcoholic and acetous and contains a specific amount of acetic acid.” Acetic acid is the predominant flavouring and antimicrobial component in vinegar and good quality vinegar should contain about 5% acetic acid. In United States legally vinegar must contain at least 4% acetic acid resulting from acetic acid fermentation of ethanol containing substrates. Vinegar is traditionally used as a food preservative because it retards microbial growth and contributes sensory properties to a number of foods.The acetic acid present in vinegar provides antiseptic and germicidal properties to vinegar and inhibits bacterial growth. The fruit vinegar has unique flavors and is superior to synthetic vinegars.
Vinegar bacteria are also known as acetic acid bacteria because they cause acetic acid fermentation. A variety of bacteria are able lead acetic acid fermentation but the bacteria belong to the genus Acetobacter and Gluconobacter are used commonly in vinegar making.The Acetobacter aceti are the most common bacteria used in vinegar preparation. They are Gram-negative, ellipsoidal to rod-shape and are able to oxidise ethyl alcohol (C2H5OH) into acetic acid (CH3CO2H) under aerobic condition at 27-370C.The Acetobacter spp. are better acetic acid producers and has inherent capacity to oxidise ethanol to acetic acid but they oxidize acetic acid to CO2 and H2O due to over-oxidation which is not a problem with Gluconobacter spp. The  A. pasterianus. A. polyoxogenes, A. europaeus, A. xylinus, A. intermedius and A. lovaniensis which is commonly used in Chinese vinegar are isolated from raw vinegrs and found to be involved in acetic acid fermentation. The acetic acid bacteria tolerate alcohol and 6-8% alcohol in mash is better for their activity. The bacteria involved in acetic acid fermentation were called Mycoderma aceti in 1862 by Pasteur. The acetic acid bacteria have been classified in the family Acetobacteriaceae and Gluconobacter  in ninth edition of Bergey’s Manual of Systematic Bacteriology.
Mother of vinegar
Mother vinegar is thick layer of substances containing cellulose and acetic acid bacteria. The layer is formed on fermenting mash and it is removed when it become heavy enough to fall.. Mother vinegar is live starter that can convert ethanol to vinegar.
The alcoholic solution used for vinegar preparation is called ‘mash’. The mash contains ethanol and some acetic acid. The sum of ethanol (vol. %) and acetic acid (g/100 ml) is called total mash concentration which gives maximum acetic acid concentration after complete fermentation. The quotient of the total mash concentration indicates the acetic acid concentration yield.
Pasteurizing vinegar
The vinegar is pasteurized to preserve and inhibit the oxidation of acetic acid into CO2 and water by checking the activity of acetic acid bacteria. In the process vinegar is filtered through cheese cloth to remove mother of vinegar film and other suspending materials then heated and filled into sterilized bottles. The capped bottles are put in hot water both and pasteurized at 140 – 1600F for 30 minutes. The pasteurized vinegar can last for several years under normal conditions.
Aging vinegar
Fresh raw vinegar is a turbid liquid and sharp biting in taste. Vinegar becomes mellow from strong sharp bite and developed pleasant flavor and aroma after aging in wooden barrels for 3-6 months. The aged vinegar must be deprived O2 otherwise acetic acid could convert into CO2 and water.
Flavoring vinegar
The garlic, ginger and herbs are added to home made vinegar for flavoring. The flavoring substances are put into cheese cloth bag that is left into vinegar 1-4 days to get desired strength of flavoring. The bag is removed after extracting the flavoring compounds into vinegar.
Acetic acid production in vinegar
The food grade acetic acid in vinegar is produced from starchy substances or sugar in the two steps fermentation: In the first step alcoholic fermentation takes place at 30-320C in which sugar is converted to ethanol in anaerobic condition by yeasts Saccharomyces cerevisiae. The starch converts first to sugar by amylase enzymes if starchy substances are used in place of sugars in vinegar making-
  • Conversion of starch to sugar by amylase enzymes
(C6H10O5 )H2O           →        C6H12O6         
Starch                               Sugar
  • Conversion of sugars to ethanol by yeasts
C6H12O6       → 2CH3CH2OH + 2CO2
Glucose                Ethanol
The second and last step is performed at 27-370C temperature with the help of acetic acid forming bacteria Acetobacter aceti aerobically in which acetic acid is produced in following two sub steps-

  • Aerobic conversion of ethanol to hydrated acetaldehyde
                  CH3CH2OH + ½O2      →        CH3CHO + H2O
Ethanol                                      Acetaldehyde
  • Dehydrogenation of acetaldehyde to acetic acid aerobically by aldehyde dehydrogenase enzyme
CH3CHO + ½O2   →              CH3COOH
Acetaldehyde                          Acetic acid
      Theoretically 1g glucose is yields 0.67g acetic acid but some glucose is consumed by acetic acid bacteria and some remains unconverted into acetic acid therefore practical yield of acetic acid in vinegar is always less than calculated theoretical yield.

Vinegar aroma and quality
The processing method, raw materials and aging influence the organoleptic properties of vinegar. The brewed vinegar not only contains acetic acid but it also contains Citric acid, lactic acid, tartaric acid and malic acid. There were about fourteen volatile compounds found in vinegar including Acetaldehyde, methanol, 1-propanol, ethyl propionate, 3-methyl-1-butanol, 2-methyl-1-butanol. The acetic acid and ethyl acetate are the major compounds in the vinegar.
Vinegar strength
The vinegar strength is described in the term of ‘Grain strength. Gain is ten times the percentage of acetic acid present in vinegar For example, 100 grain vinegar is containing 10% acetic acid in other words  vinegar having 10 per cent acetic acid is termed as vinegar of '100 grain strength’.
Types of Vinegar
Vinegars are normally named after the raw materials used in its preparation and their trade names vary from country to country in the world. The white distilled vinegar, cider vinegar, wine vinegar, rice vinegar, and malt vinegar are the common types of vinegar. The different types of vinegars can be classified in two major groups:
1.      Brewed or natural vinegars: Brewed vinegars are made by biological process in which alcoholic and subsequent acetic fermentation occur by  yeasts and acetic acid bacteria, respectively. The brewed vinegars are further classified into following types:

  •     Fruit vinegar: Vinegar prepared from the fruits such as Grapes, Apple, Orange, Jamun, Peach, Pear, Pine Apple, quince, blackcurrant, raspberries, persimmon etc. in Europe, China, South Korea and India. The colour and flavor of the vinegars vary according to fruits.
  •       Potato vinegar: The vinegar prepared from the potato starch.
  •    Molasses vinegar: is prepared from molasses a by-product of sugar manufacturing industries.
  •      Honey vinegar: is made from honey in the Italy, France and Spain. Usually low grade honey is used for the preparation of honey vinegar.
  •        Balsamic vinegar:  is prepared from Trebbiano variety of white grapes and aged in woods barrels. Balsamic vinegars are traditionally prepared in Italy and may takes many years in its ageing. The must is cooked to higher sugar concentration of about 30% before fermentation. It is brown in colour and aromatic with sweet-sour flavour.
  •      Cane vinegar: is made from sugarcane juice and popular in Philippines. It is dark yellow to golden brown in colour and free from residual sugars. It is called Sinamak in Philippines when spices are mixed with it.
  •       Champagne vinegar: is made from champagne wine and is free from bubbles.
  •      Cider vinegar: is made from apple cider a type of wine exclusively made from apple fruits. It is acidic, astringent in flavour and yellowish gold in colour.
  •      Coconut vinegar: is made from coconut water and low in acidity with a musty flavour and cloudy white in appearance.
  •      Distilled vinegar: is made from the acetic acid fermentation of distilled or synthetic ethanol. It is known as distilled spirit in UK where distilled ethanol obtained from fermented mashes is used in the preparation whereas it is called distilled vinegar in USA where petroleum ethanol is used in the preparation. It is usually colourless and lacking aroma.
  •       Malt vinegar: is prepared from fermented barley and grain mash, and flavoured with beech or birch woods. It is light brown to straw colour.
  •       Rice wine vinegar: is prepared from rice and of three types red, white and black in colour. The rice wine vinegar has been made by the Chinese for over 5,000 years. It is popular in China and Japan.
  •       Sherry vinegar: is made from sherry wine and aged in wooden barrels under the full sun. It is aromatic and dark in colour.
  •     Wine vinegar: Vinegar made from white or  red wine and is common vinegar of the Mediterranean countries and Central Europe. The slow oxidation of wines to vinegar leads to development of excellent organoleptic quality due to formation of substances like acetaldehyde and ethyl acetate.
  •      Beer vinegar: is made in the UK, Germany, Austria and Netherlands from beer. It is light golden in colour and malty in taste.
  •        Date vinegar: The date fruits are used in its making in the Middle East Countiers.
  •       Chinese vinegar: The vinegars made from rice, wheat, millets and sorghum in the China and may contain added sugar, spices and herbs are known as Chinese vinegar. It is inky black in colour with malty flavor. The ‘Shanxi’ and ‘Zhenjiang’ are the famous Chinese traditional vinegars.
  •        Palm vinegar: is made from flower clusters sap of nipa palm in the Philippines.
  •        Raisin vinegar: is made from raisin grapes in the Middle East Countries. It is light brown and cloudy in appearance with mild flavor.
2. Non-brewed or synthetic vinegars: Non-brewed vinegars are prepared by diluting synthetic acetic acid or glacial acetic acid to 4 per cent and are often coloured with caramel.
Methods of vinegar Preparation
Vinegar can be produced by different process. The demands for large amounts of the vinegar require speedy and efficient industrial fermentation to meet the demands. Many vinegar preparation processes have been developed to accelerate the production of vinegar through speedy oxidation of ethanol into acetic acid in the presence of acetic acid bacteria. The following processes have been developed for vinegar making:
  •          Home process
  •          Surface culture or Let-alone process
  •          Orleans process
  •          Quick process or Generator process
  •          Submerged culture process
·         Home process: The fruits like jamun, grapes, apple, pear, peach, plum, fig, oranges and honey, sugar syrup as well as hydrolysed starchy materials can be used for vinegar making. The ripe fruits is selected , cleaned with water, crushed or cut into pieces and blended by mixer. If the material is starchy pectic enzyme @ 50mg/kg is added and after 10 hours the extract is strained through muslin cloth. The TSS of the extract is adjusted to 12% by adding water or sugar. The extract is boiled to kill the wild yeast and other micro-organisms and filled into container up to ¾. The juice is cooled to room temperature and pure yeast starter is added @ 20g/ 20 L juice and the mouth of the container is plugged with cotton or cheese cloth so that CO2 formed into the container can escape to atmosphere. The alcoholic fermentation completes within a week at about 26-280C temperature. The cleared liquid is siphoned off and poured into another container up to ¾ volume of the container. The alcohol content is adjusted to 7-8% by diluting with water then unpasteurized mother vinegar is added in 1: 10 ration. The vinegar bacteria form a film at the surface of liquid and oxidized ethanol into acetic acid at 26-280C. The film should not be disturbed during fermentation process. Fresh vinegar is turbid liquid and raw biting in taste. Its further processing includes filtration, clarification and pasteurization. The cleared vinegar is bottled and pasteurized in hot water at 740C for 10 minutes. The ready vinegar is stored for use.
·         Surface culture or Let-alone process: It is slow process of vinegar making that is also known as Home process. The acetic acid bacteria are allowed grow and form a surface film in the barrel or vessel partially filled with vinegar stock. The vinegar is taken out after fermentation and vessel is refilled with vinegar stock for next batch. In the process the surface film of bacteria is disturbed and has to be reformed in each batch. The formation of surface film needs time and wastefully consumes fermentable substances each time.
·         Orleans process: It has been used in the Orleans region of the France since 1670 and is also called the French process of vinegar making. It is a traditional semi-continuous slow process but best to produce fine quality table vinegar of excellent flavour. The need to reform surface film and wastage of substrates as in surface culture process are overcome in the Orleans process. The wood barrels called casks are used in the process. A pipe with funnel is fitted through top of the barrel and lower end of the pipe rest into liquid of the bottom. The upper mouth of the pipe is covered with cotton to prevent the insect entry. The pipe is used to add the fresh vinegar stock without disturbing the surface film. The air holes covered with cheese cloth are made in wall of the barrel above the liquid level for air circulation. A level indicator to indicate the liquid level in the barrel and tap to drain out the ready vinegar from the barrel are also fitted in the casks. The wood barrels are filled with alcohol fermenting liquid to approximately ¾ full but level of the liquid is kept about 5 cm. below the air holes. The liquid should have about 20-25% fresh vinegar (mother). The liquid is allowed to ferment for about 1 to 3 months at 24-270C. Then 1/3 vinegar is drawn off and equal amount of alcohol fermenting liquid is added through funnel for acidification. The process is repeated till need.

·         Quick process or Generator process: The process was called trickle method of vinegar making earlier. The quick process was developed by German chemist Schutzenbach in 1832 and since then it is used for commercial vinegar production. The generator used for fermentation is a fixed bed microbial film reactor in which a thick slim coating of bacteria grows around a non-compacting material like beech wood shavings, charcoal or coke packed into large upright wood tanks above a perforated wood grating floor. The re-circulating fermenting liquid trickles over the packing toward the bottom whereas air moves from the bottom toward the top through air holes. The rate of vinegar production depends upon oxygen availability because air supply controls the oxidation of ethanol into acetic acid. The both acetic acid production and generator temperature are directly proportional to the air supply. The process takes about 3 to 7 days to complete. The 2/3 of ready vinegar is drawn off from the generator and fresh fermenting liquid is poured into the generator slowly until desired level for fermentation. The optimum temperature for quick process is 30 to 320C.  
·         Submerged culture process: The many methods of submerged culture process such as Frings Acetator, Yeoman’s Cavitator, Bourgeois Process, Fardon Process and Vinegator Process have been developed making of vinegar at industrial scale. The submerged culture process provides congenial conditions like aeration, stirring and temperature control require for speedy acetification of vinegar stock. The fermentors used in the process are fitted with thermostat and cool device to control the temperature, aerator and pump to aerate and stir the fermenting liquid. The mash is stirred and aerated frequently to speed up the acetification process. The acetic acid bacteria are most sensitive to O2 and acetification rate decreases if bacteria are deprived from O2 even for short period. An interruption of O2 supply even for 1 minute or more completely stops the acetification and there is no recovery even when full aeration is resumed in the process. The ½ of the liquid is pumped off from the fermentor when 0.1-0.3% (v/v) ethanol left in the liquid to oxidise into acetic acid and empty ½ volume is filled with fresh vinegar stock for further oxidation. The submerged culture process is faster but needs higher capital investment.
Vinegar uses: Vinegars are used in salad dressing, ketchup and sauces making and in Chinese dishes. Vinegar is also used in pickle preparation particularly in instant pickles. The spiced vinegars are eaten with chapatti prepared from coarse grains and has become a part of modern cooking. The jamun vinegar is supposed to be of medicinal important and used in diabetics. 
Vinegar problems

  •          Growth of lactic acid bacteria: Vinegar quality lowers if the lactic acid bacteria grow in fermented mash. The bacteria cause cloudiness, disagreeable mousy flavor and interfere with acetic acid fermentation. The problem can be controlled by adding starter of pure yeast for alcoholic fermentation and mother vinegar or unpasteurized vinegar for acidification of ethanol.
  •          Wine flavour: If the fermented juice is unnecessarily expose to air a kind of yeast film grow on the surface of the liquid that causes cloudiness. The problem can be controlled by spreading of neutral oil or liquid paraffin wax over the surface of the fermented liquid, adding 20-25% unpasteurized vinegar and filling the barrels to the brim these measures minimize the exposure to air.
  •          Vinegar insects: The vinegar fly (Drosophila cellaris) propagates on the rotten fruits and vinegars. Although the vinegar flies cannot destroy the quality of vinegar yet they act as a barrier during fermentation. The vinegar eels, vinegar Louse and vinegar mites are the other undesirable insects of vinegars. The vinegar insects’ problem can be avoided by maintaining proper sanitary conditions.
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