The greatest cause of failure in vinegar making is carelessness on the part of the operator. Intelligent separation should be made of the process into its various steps from the beginning to end.

PRESSING THE JUICE

The apples should be clean and ripe. If not clean, undesirable fermentations may develop which will injure the quality of the finished product. Fruit which is just ripe contains the maximum amount of sugar. If the fruit is too green or over-ripe there may not be sufficient sugar present for the final production of a per cent acetic acid. Dirt, grass, leaves, rotten and wormy fruit bear millions of bacteria, some of which are sure to be of undesirable varieties. These may be the cause of bad flavors, and may make the vinegar low in acid, off-color, and turbid.

The pomace should never be watered or steamed and run thru the mill or pres a second time. However, some cider manufacturers will put the pomace thru a second time. However, some cider manufacturers will put the pomace thru second time without wetting. If water is added at the point or at any later point, there is danger that the juice may be too dilute to produce the required acidity.

SETTLING OF THE JUICE

If sweet cider is allowed to stand quietly a considerable amount of sediment is found to accumulate. This material contains impurities and bacteria which are undesirable. It is, therefore, preferable to allow the sweet cider to stand in a cold place for a few days until the suspended matter has settled. The clear upper part of the liquid is drawn (“racked”)off. If much liquid remains with the sediment it may be strained thru cloth. If the cloth is made up in the form of a bag it should only be allowed to drain and not be squeezed since this would force much of the sediment thru the pores of the cloth. If the sediment is not removed at this time and later times when it is advised, it may be the cause of undesirable flavors, and also it may contain bacteria which will actually interfere with the processes of fermentation.

FERMENTATION OF THE SWEET JUICE

It is most important to remember that the production of vinegar from fruit juice takes place in two distinct steps. The first is the formation of hard cider, when the sugar in the juice is change to alcohol.

The sweet apple juice should be placed in a clean cask. If an open-top barrel or tank is used, it should be covered with a lid or heavy cloth such as oilcloth. A barrel or cask which has contained vinegar should not be used, or if such a container must be used, it should be first washed with boiling water. More vinegar is spoiled in the making by the cider being put into old vinegar barrels containing dregs and impure “mother” than by any other mistakes. Thruout the entire process, in fact, all utensils and apparatus used should be scrupulously cleaned.

Metal containers should be avoided, but if used must be heavily paraffined. Stoneware vessels are satisfactory.

If good, fresh yeast cake can be obtained it may be added in the proportion of one cake to each five gallons of cider. A cake is to be macerated in a quart of cider until it is in a smooth liquid condition. This is then mixed with the main body of the liquid. Yeast of doubtful quality which has not been kept in a cold place should not be used since it may contain undesirable bacteria.

If pasteurized cider is used it is absolutely necessary either to add the yeast or to mix the pasteurized cider with some raw cider. This is because the yeast organisms, tho always present in raw juice, are destroyed when heated and are not, therefore, present in pasteurized cider. To allow sufficient space for foam, the casks should be filled not more than three-fourths full. The casks should then be stored in a place where they are exposed to a medium temperature of about 70º F. The best results are not obtained if containers are placed in a cold cellar. Neither should they be kept at the temperature of an overheated room. In the autumn of spring the containers may be set out in the sun. There is “vinegar farm” in Kansas where all operations are carried on out-of-doors.

The opening of the container should be covered with cheese cloth to prevent the entrance of insects, but must not be stoppered tightly. Within a few days a violent fermentation will begin which is evidenced by considerable frothing and a noise like the buzzing of bees. This is due to the production of a gas—carbon dioxide.  This will continue a few days, and then it becomes less evident.  In this condition the material should be kept from a few weeks to a few months depending on the need for the finished product.  The longer the time which is allowed at this point the better will be the vinegar produced.

This finishes the first step of the process.  Hard cider is the result and no acetic acid will have been formed to this point unless it was formed during the storage period following the active fermentation.  The cider may taste sour but this is due to the natural acid from the original fruit made more noticeable on account of the absence of sugar.

During this time the containers must be allowed to stand undisturbed, when it will be found that considerable sediment has formed.  From this the clear liquid is now to be separated.  That portion standing well above the sediment may be siphoned off by use of a hose while the remainder can be strained thru a cloth.  Again the cloth should not be squeezed. To be continued…

ACETIC FERMENTATION

In the alcoholic fermentation care was taken to keep air away from the liquid.  The acid bacteria, on the other had, do not grow in absence of air and will grow and produce acid faster the more air that is supplied.  Therefore, in this second operation there should be air circulation over the top of the liquid.  At the same time open exposure to the atmosphere such as would be occasioned n a open top barrel is to be avoided on account of loss from evaporation.

When it is desired to have the acetic acid fermentation begin, the clear hard cider may be transferred to a cask which has previously contained good vinegar or it may be put back in the same cask after cleaning.  In either case the container should be not more than three-fourths full, and the stopper should be left out for the entrance of air.  The opening must be covered with cheese cloth or lightly plugged with cotton.

It is highly desirable at this point, but not absolutely necessary, to add some good vinegar, or “mother” in order to insure the presence of a large number of bacteria.  Pasteurized or chemically-preserved vinegar would be of no use.  If good old vinegar is available, add in the proportion of one pint to five gallons of cider.

Pure mother is the thin, clear glistening, gelatinous membrane that come to the top of good vinegar.  It is light colored and clear.  If it gives the appearance of a tough, leathery, brown mass it is contaminated and should never be put into hard cider.

As before, the containers should be held in a room at the temperature of 65° to 75° F.  During this stage, bacteria are changing alcohol to acetic acid.  This necessarily a slow process which will require not less that three months and which may require a year or more, depending upon the temperature and the number and kinds of bacteria present.  On the average, vinegar may be expected to be finished in six months where the temperature is 70°, while at a temperature of 50°, two years may be required.  This will give an idea of the great influence of temperature.

On account of the necessity of air, acetic acid formation takes place only at the surface of the liquid where the film of mother forms.  This must not be disturbed.  If the container is moved so as to agitate the contents, this film may sink to the bottom and the process will be retarded until a new film has time to form.

The operation of transforming hard cider to vinegar may be modified as follows:  When a cask of vinegar is found to have reached  the required acidity and is of good quality, about two-thirds is removed, care being taken to leave the scum behind.  To the remaining third is added an amount of hard cider equal to that removed.  In from one to three months this will have the required acidity, and the operation many be repeated indefinitely, unless abnormal fermentations get started which are evidenced by poor flavors in the finished product or its refusal to come up to standard.

It would be fatal, operating in this way, to add sweet cider to the vinegar barrel.  If this were done the second lot would never come up to standard.

THE FINISHED PRODUCT

The law requires that vinegar offered for sale shall contain 4 per cent acetic acid.  There is no simple way for the home testing of vinegar of acetic acid, yet its acidity should always be determined before it offered for sale.  There are in some states regulations concerning the percentage of solids and ash which most be present, but any apple-cider vinegar properly and honestly made will meet the requirements on these points.  On the other hand, a producer may honestly believe that his vinegar is marketable when it may be found to be below the requirements of law with regard to acidity.

When it is believed that fermentation is complete and the vinegar is of satisfactory acidity, a sample of about four ounces my be sent to any chemical laboratory for analysis.  This College is prepared and will make such test free of charge to all individuals.  Samples would be addressed as follows:  Department of Chemistry, College of Agriculture, Cornell University, Ithaca, New York.

If the chemical analysis shows that the vinegar is well over 4 percent in acetic acid, the clear liquid is drawn off from any sediment or surface film and may also be passed thru a flannel bag.  Clean casks, jugs, or bottles may be used for filling, but iit is  important that they be filled entirely full and tightly stoppered.  If these precautions are followed air is thus excluded from the product and it may be expected to preserve its strength indefinitely.  Wherever air is allowed to come in contact with finished vinegar the bacteria attack the acetic acid, reducing the amount present.  Thus a vinegar which has once been above government standard may deteriorate to such extent that it is unlawful to sell it.  If the air is kept away no such action need be feared.

The same effect may be accomplished by pasteurization of the finished vinegar.  In this way the bacteria which might break down the acetic acid are destroyed.  However, even tho the vinegar be pasteurized it is best to take precautions to exclude air from the containers because the bacteria doing the damage are present everywhere and might get into the product after it had been given the heat treatment.

The longer the storage of vinegar will usually speak of “grain vinegar” instead of the percentage acetic acid.  When he speaks of a 40-grain vinegar it is same as if he described it as containing 4 per cent acetic acid.  Fifty-grain vinegar is equivalent to 5 per cent acetic acid, and so on.  There are various explanations for the origin of the term grain, but it is sufficient to remember that the grain number divided by 10 gives the percentage of acetic acid.

From The Preparation of Marketable Vinegar by Frank E. Rice – Cornell Extension Bulletin #40, April 1920 published by the New York State College of Agriculture at Cornell University, Ithaca, New York.