If honey and water in proper proportions be exposed to the atmosphere, at a suitable temperature, for a sufficient length of time, acetic fermentation will in due course ensue. At the same time, to obtain the best results, careful attention must be given to certain details, and various precautions taken. The alcoholic ferment must be carried on under suitable conditions, in order that it may be complete. The temperature must be neither too high, nor too low. Suitable and sufficient nutrient material also for the ferment germ must be present; that is a proper proportion of nitrogenous matter, together with certain inorganic salts, which may be added in the form of a little ammonium phosphate and potassium tartrate. The acetic fermentation which follows must also be regulated with due care, and not allowed to continue longer than necessary, or deterioration of the liquor will take place with a gradual loss of acidity. The fining also of the liquor must be carefully attended to, in order to render it perfectly clear and bright. And finally, it is only when the alcoholic and acetic fermentations have been effected, in a completely satisfactory manner, and the vinegar stored for a sufficiently long period under the most suitable conditions, that the ripening process is effected, without which it will be found lacking in that agreeable flavour and aroma which are its special characteristics. [Sidenote: Proportion of Honey to Water.] In the first place, we have to determine the proper proportion of honey to water. Commercial Vinegar is required by law to contain a minimum of 3 per cent. acetic acid.[2] Proof Vinegar contains 5.4 per cent., with a specific gravity of 1.006 to 1.019. For all ordinary purposes this is a convenient strength and first-class vinegars contain about this percentage. Of course, the percentage of acetic acid is dependent on a satisfactory alcoholic fermentation and suitable conditions for the development of the acetic germ; but, supposing the conditions favourable, it is possible to obtain from an aqueous solution of 1 part honey to 8 of water, about 5 per cent. acetic acid. A suitable proportion will thus be 1 part honey to from 7 to 8 parts of water by weight. [Sidenote: Suitable Receptacles.] When made in small quantities almost any open vessel will serve as a receptacle for the liquor, always excepting glazed or metal ones, in which vinegar must never be allowed to stand. Owing to the solvent effects of the acid, the liquor is, in these cases, liable to be injuriously contaminated. The vessel used should be covered with muslin or cream cloth, to protect from insects, etc. A small cask is also a convenient receptacle, but this should not be filled more than three parts full and the bung hole must be left open, protected with gauze or other coarse material.[3] [Sidenote: Starting the Fermentation.]