This medium is maintained at a temperature of about 37° C. (the most favourable temperature for the fermentation) until the required bacterial action is completed, the time necessary being about seven days, and to each litre of the liquid thus obtained there are added from 2 to 6 grs. of lactic acid. Acetic or other similar organic acid may be used instead of the lactic acid, but sulphuric or mineral acids must not be used. The acid liquid is afterwards neutralized by ammonia, which is added when the bate is to be used, and there are then formed certain chemical compounds similar to those found in a dung bate. The addition of the acid to the nutrient medium will immediately stop the growth of bacteria, but the acid is not added for that particular reason, but for the particular purpose set forth. Instead of the enzymes obtained from the bacteria of dung, other enzymes of a similar character may be used, such as the enzymes obtained from the bacteria found on skins during the sweating process. For bating skins in a practical manner with the improved bate herein set forth, the method of using the same is preferably varied according to the skins to be treated and the kind of leather it is required to produce. Thus for kid skins, skivers and other skins for which dog dung has hitherto been used, the skins, after the liming process, are first well washed in water in the usual way to remove the bulk of the lime. The skins are then placed in a wheel or paddle with the bate prepared as before described, with the acid exactly neutralized by the ammonia or so nearly neutralized that the alkaline action of the skins will complete the neutralization, all skins being alkaline when introduced into the bate. The bate is diluted according to the amount of liming the skins have undergone, and when in the paddle or wheel the skins and bate are maintained at a temperature of about 37° C., and the skins paddled until they have “fallen” considerably. The skins are then removed from the wheel or paddle and scudded preferably on the “grain” side, after which they are returned to the wheel or paddle and the paddling continued until the bating action is completed, this being judged in the usual way by a practical tanner according to the feel of the skins. The strength of the bate after the scudding process may be varied if found desirable. After the bating process is completed the skins are treated in the usual manner.