(Scanned in from the Long Ashton Research Station Annual Report for 1917 pp 18-20)
Several enquiries have been received during the year as to the value of cider vinegar as a substitute for malt vinegar. Supplies of the latter are becoming short owing to the war, and the provision of adequate supplies of some other form of vinegar may become necessary. Cider vinegar is a satisfactory substitute and could be produced in considerable quantity if the necessity arose. A few notes on its method of manufacture are therefore given.
When cider is exposed to the influence of the air it goes quickly hard or sour and gradually turns into vinegar. It has been mentioned in earlier reports that this transformation is due to the action of bacteria, which by means of the oxygen in the air transform the alcohol contained in the cider into acetic acid, acetic acid being the chief constituent of vinegar. Thus cider-vinegar is the final product of a disorder known as acetification. To produce vinegar from apple juice two separate fermentations are necessary, namely, first the alcoholic fermentation brought about by a yeast, by which the sugars in the apple juice are fermented into alcohol and carbonic acid gas, and secondly the acetic fermentation caused by bacteria, by which the alcohol is oxidised into acetic acid. Finally, if the vinegar is left for a long time exposed to the air the acetic acid is gradually transformed into carbonic acid gas.
The vinegar made from cider will contain all the constituents of the cider resulting from the alcoholic fermentation of the apple juice with exception of the alcohol, which is more or less completely turned into acetic acid. To make a good vinegar from cider it must be made from pure apple juice fermented to dryness and containing 4 to 5 per cent of alcohol by weight. By the acetic fermentation, the alcohol should theoretically be transformed into acetic acid in the proportion 46 parts of alcohol to 60 parts of acetic acid. In practice this proportion cannot, however, be maintained, partly because a little alcohol always remains in the vinegar, partly because of evaporation during the fermentation. The proportion to expect would be as about 4 to 5, so that a cider containing 4 per cent. by weight of alcohol should give a vinegar with 5 per cent of acetic acid
To make vinegar from cider the following three conditions are necessary : (1) The presence in the cider of the acetic ferment; (2) Access of air; and (3) Temperature of 65° -85°F. The acetic ferment is present in all unpasteurized ciders, and one has only to leave a bottle open for some time at a convenient temperature to see it develop as a thick, leathery film on the surface of the liquid. This film consists of a small rod-bacterium (Bacterium xylinum). To get a quick development of this "vinegar plant" a little vinegar can be added to the cider placed in an open vessel at a temperature of about 75°F. Editor's note: this is only possible with unpasteurised vinegar as would have been usual at that time. Twenty-first century vinegars are no longer 'alive' and so will not act as a starter! Modern ciders, even if unpasteurised, contain very little 'acetic ferment'! Leaving apple pomace open to the air is the best way of acquiring the required bacteria (see The Science of Cidermaking Part 6)
A small vinegar-making plant for household purposes can easily be constructed in the following way. An ordinary cask with a capacity of, say, 6 gallons, is filled a little over halfway with a dry, completely fermented cider. To the cider can be added a little good vinegar (see note above). The cask is placed upon its side, provided with a wooden tap, and a hole of about one inch diameter is bored in each end; one of the holes about one inch over the surface of the liquid in the cask, the hole in the other end close to the top. In the bunghole is inserted a small glass funnel, to which is attached a piece of rubber tubing dipping into the cider. To prevent access of the so-called vinegar flies, which deposit their eggs in the vinegar, the holes and the funnel are covered with a little fine gauze (cheesecloth). The cask is placed in a warm room, and the vinegar making will soon start.
After about two months a sample is taken out through the tap, and if the temperature of the room has been sufficiently high, the vinegar will be ready for consumption. If the room has not been warm enough the process will take longer time, e.g., 4 to 6 months. Thus vinegar can be made continuously by replacing the vinegar drawn off with dry cider poured in through the funnel.
With an apparatus constructed as above some very good cider vinegar has been made at the Institute. The vinegar was made from a dry cider containing 4.5 per cent of alcohol by weight. It was perfectly clear when drawn from the cask, but after some time it became cloudy in bottles. This cloudiness can be overcome by storing the vinegar in closed vessels for some months and racking or filtering. If the vinegar is wanted quickly for bottling, the easiest way to prevent cloudiness setting in is to pasteurize the bottled vinegar by placing the bottles in a waterbath or steriliser, which is slowly heated to a temperature of 140° F and kept at that temperature for 15 minutes. Cloudy vinegar can also be cleared by filtering or by first adding a clearing agent such as milk, which is used in the proportion of ¼ to ½ per cent., i.e., ¼ to ½ gallon of milk per 100 gallons of cider. Vinegar prepared upon these lines has been used successfully for pickling purposes.
If it is desired to make vinegar from cider on a large scale a more
elaborate apparatus is wanted of a similar construction to the vinegar-makers
used in malt-vinegar factories, or as used for making vinegar from wine.
This apparatus generally consists of a cylindrical wooden vat placed upon
its end with two perforated wooden discs placed with an interval of varying
height, the one above the other, near the top of the vat. Between the two
discs is placed a layer of coarse wooden shavings or other similar material
presenting a large surface. In the holes of the upper disc are often placed
short lengths of cord hanging down in the layer of shavings, so as to distribute
the liquid as evenly as possible. The vat has a certain number of air holes,
so as to permit the air free access, and is kept in a warm room. The liquid
to be acetified is pumped in over the top disc and slowly spreads over
the wooden shavings, where it is exposed to the influence of the air, and
the process of acetification soon starts. The acetified liquid is drawn
out from the bottom of the cask and again pumped into the top of a vinegar-maker,
and this process is repeated until the vinegar has the desired strength,
which is usually from 4 to 6 per cent of acetic acid. In the first instance
the vinegar-maker is generally started with a pure culture of the acetic
ferment. With an apparatus as outlined in the above it is possible to transform
cider into vinegar at a quick rate.
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Added by Andrew Lea 1st October 2001