Acetic Acid- Vinegar-

 vinaigre (F) = sour wine

•         Acetic acid product-minimum of 4% of acetic acid

•         produced   by the process of double fermentation, alcoholic and acetous fermentation, from a suitable raw material of agricultural origin, containing starch, sugars or starch and sugars,

•         sugary/starch materials undergo alcoholic fermentation by yeasts followed by an acetuous one (oxidation of alcohol to acetic acid) by acetic acid bacteria

•         Commonly used in food preparations - pickling, salad dressings, sauces and mayonnaise

•         Variety of industrial, medical, horticultural and domestic uses

•         medicinal, laboratory, and cleaning purposes, cooking, baking, meat preservation, and pickling

Kinds of VINEGAR    

•         Raw material - Low cost raw material which supports the growth and metabolism of acetic acid bacteria

•         different starting materials - fruits, starchy vegetables, malted cereals,, sugars, spirits/alcohol etc

Product named as per the raw material used

•         Malt vinegar (alegar) - grains like barley

•         Wine vinegar - red or white wine

•         Sherry vinegar - Sherry wines

•         Cider vinegar - apple

•         Fruit vinegars - fruit wines, no additional flavoring - apple, raspberry, tomato etc

•         Balsamic vinegar from the concentrated juice, or must, of white grapes - an aromatic, aged type of vinegar - Italy –

•         Rice vinegar - East and Southeast Asia

•         Coconut vinegar, from fermented coconut water - Southeast Asia

•         Palm vinegar, from the fermented sap from flower clusters of palm - Philippines

•         Cane vinegar, from sugarcane juice - Philippines

•         Raisin, date, beer, flavored vinegars –fruits n herbs

•         Kombucha vinegar from kombucha, a symbiotic culture of yeast and bacteria - flavored by adding strawberries, blackberries, mint, or blueberries at the beginning of fermentation.

•         Distilled vinegar - Any type of vinegar may be distilled to produce a colorless solution of about 5% to 8% acetic acid in water -distilled spirit or "virgin" vinegar or white vinegar

•         Spirit vinegar - stronger variety (5% to 20% acetic acid) - made from sugar cane or from chemically produced acetic acid

 Microbial Fermentation Process 

 Two-stage fermentation

Ø  fermentable sugars are converted into ethanol by the action of yeasts (Alcoholic fermentation)

Ø  ethyl alcohol oxidized to acetic acid; by Acetobacter and Gluconobacter (Acetic acid fermentation)

Ø  Acetobacter/Glucunobacter - natural micro flora of plant products

Ø  Vinegar production are less susceptible to microbial contamination

Ø  pH of vinegar - 3 or below

Ø  Possible to carry it out in simple vessels such as open vats of wood or concrete

Ø  Acetic acid and Ethanol required for optimal growth of Acetobacter

Ø  Ethanol not less than 0.2% and not more than 5% (v/v)

Ø  The maximum concentration of acetic acid that can be produced by fermentation is usually around 10-15%

 Alcoholic fermentation

Ø  Sugar conc: 8-20%

Ø  Potassium and ammonium phosphates added if required (eg. With honey) – not needed in case of wine/apple juice.

Ø  pH 4.8-5. Temp: 28-30 degree celsius 3-7 days; in open fermentation vats

Ø  SO₂ added to inhibit the growth of contaminating microorganisms

Acetic Acid fermentation

Commercial vinegar production either by fast or slow fermentation processes.

Slow methods - traditional vinegars; fermentation proceeds slowly over the course of weeks or months-  Here, the fermenting liquid is not moved during acetification. Fruit juices or malt liquors are the starting material, usually eg., Open-vat (French/Orleans) method or home/let alone method –  culinary vinegar

Ø   The longer fermentation period allows for the accumulation of a nontoxic slime composed of acetic acid bacteria- mother of vinegar 

Fast methods - Here, the fermenting liquid is in motion- usually spirit/alcohol is the starting material for acetification. Add mother of vinegar to the fermenting liquid; provide aeration using a venturi pump system or a turbine to promote oxygenation to obtain the fastest fermentation. Vinegar produced in a period of 20 hours to three days. Eg., Trickle (Quick vinegar) method; Vinegar generator/fogging method, Bubble method; submerged (deep) fermentation

Mother of vinegar

-           A film of vinegar bacteria trapped in nontoxic slime at the top

-           Exocellulose produced by Acetobacter sp.  (aerobic; inhibited by salt)

-          Removed by filtering - Can be used as inoculum for a fresh batch of Vinegar

-          Produced only in slow methods

-           Slime production decreases as conc. of acetic acid in the finished product increases

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v  Home/Let alone method/Batch process

Ø  fermenting fresh fruit juice such as apple juice is allowed to undergo spontaneous alcoholic fermentation to produce about 11-13% alcohol., by yeasts present

Ø  Then a barrel is partially filled with fermented juice and allowed to undergo acetification, by acetic acid bacteria, naturally present, till vinegar is produced

Ø  Slow process; Low yield; inferior quality

v  Orleans Process/French method/Continuous process

•      Oldest and well known method for the production of vinegar

•      a slow, continuous process-fermentation in large (200 litre) capacity barrels

v  Wine or cider is fermented in wooden barrels or covered vats

v  A starter culture ie., Raw vinegar from a previous run added about 1/4^th or 1/5^th of the barrel–introduces active vinegar bacteria and acidifies the wine/malt liquor/cider –

v  Enough of alcoholicsolution  is added to the vinegar to fill about half of the barrel, leaving an air space above

v  The acetic acid bacteria growing on top as a film carry out oxidation of alcohol to acetic acid at about 29⁰C for weeks to months

v  Fermentation is continued until the acetification is complete

v  Part of vinegar bottled off; equal quantity of alcoholic liquor replaced in the barrel-about 3/4 of the vinegar drawn off and replaced with fresh wine or other fermentable liquid

v  The process repeated as long as quality vinegar can still be produced

v  Continuous process- Vinegar of very high quality

v  very slow (several weeks) and is usually done in small batches

v  Dropping of the film of vinegar bacteria during the process is avoided since it can interfere with the acetification process- use a floating framework which supports the film

v  Trickling (Rapid) generator(Schutzenbach) / German method

•      Orleans process is slow -Other methods to speed up the process

•      Generator method - German method

•      A simple generator is a cylindrical tank with two chambers -  larger (upper) chamber is packed with solid materials almost to the top (wood shavings, corncobs etc.) (bacteria attach to it) - separated from the lower chamber by a screen.

•      The tank is not allowed to fill as that would exclude oxygen which is necessary for the fermentation

•      The fermenting liquids –alcohol/spirit, usually, is fed through the top of the material, through a sparger/sprinkling device

•      It trickles down/ percolates through the solid material on which a slimy growth of acetic acid bacteria is developed, which oxidises alcohol to acetic acid.

•      Air enter through the bottom screen and through the solid materials & rises up

•      The resulting liquid is then pumped back to the top & recirculated until the alcohol content is reduced to ½ percent.

•      Once sufficient acetification is done, the vinegar is drawn off and fresh alcoholic solution is added. Some vinegar may be added to the fresh alcoholic solution to kick start acetification process

•      Fermentation process releases heat-so temperature maintained at 29-30⁰C-by using cooling coils, by adjusting the rate of feeding air and alcoholic liquid or by cooling the fermenting liquid that is recirculated

                      

Fring’s generator - Vinegar Generator

v  Mackin process/ fogging method

•      A fog or fine mist of a mixture of vinegar bacteria and nutrient alcohol solution is sprayed into a chamber

•      The mist is kept in circulation by filtered air and then allowed to settle at the bottom, cooled and the returned to the top.

•      The process is continued until oxidation of the alcohol (acetification) is complete.

 v  Dipping generator is a tank with a basket filled with beech wood shavings that can be raised out of or lowered into a dilute alcoholic solution in the lower part of the tank

•      While the basket is out of the liquid, aeration permits rapid acetification by vinegar bacteria attached on the shavings

•      When the basket is in the liquid, culture is added and produced vinegar is removed

 v  Submerged/deep fermentation (bubbling)

•         Stainless steel tanks, stirred from the bottom

•         Medium containing 8-12% alcohol inoculated with Acetobacter acetigenum and A. pasteurianum, maintained at 24-29 ⁰C with controlled aeration

•         Continuous stirring and agitation using propellers

•         Heat exchangers and foam eliminators used as per need

•         Production rate 10 times higher than surface fermentation and 5% higher than trickling generator process

•         Lower investment, low personnel requirement – complete automation

Acetator and Cavitator

•         Especially for vinegar production two different fermenters are designed - provide high aeration required.

•         Automatic temperature control is available.

•         Neither fermenter has shavings/packing material, therefore no clogging.

•         They are automated for charging with alcoholic solution and discharging of completed fermentation broth.

•         They are very small and highly efficient and produce acetic acid at  higher rate.

 •         Acetators operates in semibatch mode and cavitator in continuous mode. Aeration in acetator is by fast rotating ceramic disc over an air nozzle to provide finely dispersed air bubbles. Whereas in cavitator, nutrient liquid and air are sucked down a hollow tube extending from the liquid surface so that agitation and cavitation can cause air bubbles. 

Recovery

ü  Raw vinegar is normally cloudy with suspended bacteria and other particles

ü  Clarified by filtration

ü  Potassium ferricyanide used to decolourize the final product

ü  Product is either hot-filled into bottles after treatment or pasteurized in the bottle

Finishing

ü  After acetification, vinegar is usually matured in full closed vats for up to a year

ü  During this time, it develops its characteristic flavor and aroma and some settlement on unstable colloids takes place

ü   The preservative action of vinegar is due to its acetic acid content - inhibit the growth of most food poisoning and spore-forming bacteria

ü  Bacterial growth and turbidity in bottled vinegar can be prevented by a heat treatment- Gram negative acetic acid bacteria is not heat resistant, so use 60⁰C for few minutes is enough to eliminate the numbers encountered

ü  Individual vinegars - particular flavor according to the process and the raw material used

Vinegar Defects

ü   A haze or precipitate - in vinegars that have been in contact with non-acid resistant materials- due to the formation of iron and copper (metal-containing precipitates), which spoil the appearance of vinegar and make it unsuitable for use in pickling

ü  Microbial Contamination Lactobacillus or Leuconostoc species-off-flavours

Excessive sliminess caused by some vinegar bacteria such as Acetobacter xylinum which          interferes with acetification and lead to destruction of acetic acid

ü  Undesirable acid production by butyric acid bacteria, under anaerobic conditions. 

ü  Vinegar eels (Turbatrix aceti)

nematodes occurring in some forms of vinegar, if left open - occur in naturally fermenting vinegar- feed on the mother of vinegar

                   

Acetator & Cavitator