Vinegar is defined as a condiment made from starchy material by an alcoholic fermentation followed by acetone fermentation. It is a product resulting from the conversion of alcohol to acetic acid by acetic acid bacteria, Acetobacter spp. Acetic acid is the major component of vinegar.
Also ethyl acetate is formed from the reaction between acetic acid and ethanol. The other compounds in different types of vinegar include non-volatile organic acids such as malic, citric, succinic and lactic acids; unfermented and unfermentable sugars; oxidized alcohol and acetaldehyde, acetoin, phosphate, chloride and other ions.
Vinegar is normally a product of either alcoholic fermentation by yeast or the production of acetic acid from the alcohol by acetic acid bacteria. There is no distillation between the two fermentations and the vinegar may or may not be flavored.
The most important types of vinegar are:
(i) Cider Vinegar, Apple Vinegar:
It is vinegar produced from fermented apple juice and non-grape fruits.
Wine vinegar is fermented grape juice malt.
(iv) Sugar, Glucose and Dried Fruits:
The vinegar from sugar syrup or molasses is called sugar vinegar, while that from D-glucose and dried fruits is known as glucose vinegar.
This type of vinegar made from distilled alcohol. It is otherwise known as ‘white distilled vinegar’ and ‘grain vinegar’.
White distilled vinegars are flavored with the addition of herbs, spices or other seasonings such as garlic, basil and tarragon.
Microorganisms in Vinegar Production:
The most popular bacteria involved in vinegar production is Acetobacter spp. and Gluconobater sps. The important species are Gluconobacter oxydans, Acetobacter xylinum, Acetobacter europaeus and Acetobacter vinellandii. Strains of acetic acid bacteria to be used in industrial production of vinegar because of many reasons.
(i) It can tolerate high concentrations of acetic acid.
(ii) It requires small amounts of nutrient.
(iii) It is not over oxidize the acetic acid formed.
(iv) It produces high concentration of acetic acid.
The biochemical processes are simple and are shown below:
Theoretically, 1 gm of alcohol should yield 1.304 gm of acetic acid. But it will not produce that much quantity of acetic acid. The above reactions shows one mole of ethanol will yield one mole of acetic acid and more of water. It can be calculated that 1 gallon of 12% alcohol will yield 1 gal. of 12.4% acetic acid.
Industrially vinegar is produced by three methods:
1. Slow vinegar method (Orleans method),
2. Quick vinegar process (trickling generator method), and
3. Submerged method.
It is the oldest method of vinegar production otherwise known as ‘let alone’ method in which wine left in open vats became converted to vinegar by acetic acid bacteria entering it from the atmosphere. Later the wine was put in casks and left in the open field in the ‘fielding processes’.
A small amount of vinegar was introduced into a cask of wine to help initiate fermentation. The introduced vinegar lowered the pH and inhibiting other bacteria and promotes the growth of acetic acid bacteria. The casks are made up of wood and should not fill beyond about two-thirds of its capacity, so that there was always a large amount of air available above the wine.
A thick film of acetic acid bacteria formed on the wine and converted it in to vinegar in about five weeks. About 10-20% of the vinegar was drawn off at weekly intervals and replaced with new wine. The main advantage of this method was it produces good quality vinegar.
The method has many disadvantages:
(a) It was slow method taking up to five weeks, hence; it is also known as the slow method,
(b) The yield is very less, and
(c) The ‘mother of vinegar’ filled the cask and effectively killed the process.
Quick method of vinegar production involves the movement of the alcoholic liquid during the process of acetification. In this method liquid is trickled over surfaces on which film of the acetic acid bacteria have been grown in presence adequate supply of water. The generator for this method is a cylindrical tank usually made up of wood.
The interior part of tank consists of three parts. The upper part, the region in which alcoholic liquid is allowed. The middle part, the region in which liquid is allowed to trickle down over beech wood shavings and bottom section, the region in which vinegar is collected.
The alcoholic liquid is introduced at the top through a sprinkling device and trickled over the beech wood shavings or other materials contain a layer of acetic acid bacteria which oxidizes alcohol to acetic acid. Air enters through the middle section and warm, rises and vented above. The cooling water in the heat exchanger is used to regulate the temperature in the generator so that it is between 29°C and 35°C; this is determined with thermometers placed at different levels of the generator.
The most common type of trickling generator is Frings generator. It is large, cylindrical airtight tank equipment with a sprinkler at the top, cooling coil in the middle part containing beech wood shavings and facilitates for the recirculation of the vinegar from the bottom collection chamber through the system.
Modern types of these generators are fulfilled with automatic controls for feeding the alcohol liquid, for introducing filtered air, for controlling temperature and for recirculating the liquid collected at the bottom. These generators gives high yields of acetic acid and leave little amount of alcohol.
3. Submerged Fermentation Process:
In submerged fermentation a stirred medium containing alcohol is inoculated with suitable strain of Acetobacter or Gluconobacter with a temperature range at 24 to 29°C. The bacteria grow in a suspension of fine air bubbles and fermenting alcohol. The suspension is produced by an aerator. The common feature in all submerged vinegar production is that the aeration must be very vigorous as shortage of oxygen because of the highly acid conditions of submerged production, would result in the death of the bacteria within 30 seconds.
Furthermore, because a lot of heat is released an efficient cooling system must be provided. All submerged vinegar is turbid because of the high bacterial content and have to be filtered. The most common submerged generators for vinegar production are Frings acetator, cavitators and tower fermentor.
Clarification and Packaging of Vinegar:
Vinegar is clarified careful by filtration using a filter aid such as diatomaceous earth. Vinegar from trickling generators are less turbid than those from submerged fermentations because a high proportion of the bacterial population responsible for the acetification is held back on the shavings. After clarification it is pasteurized at 60-65°C for 30 minutes.
Vinegar can be concentrated by freezing then the resulting slurry is centrifuged to separate the ice and produce the concentrate. Concentration is necessitated by two considerations. One is the reduction in transportation costs. The other is the need to prevent loss of activity of the vinegar when cucumbers were picked in it after first being soaked in brine.