Experiments with a small-scale artificial rumen have shown that of forty-two compounds tested the majority were fermented, as judged by the production of volatile fatty acids, but methane production was associated only with the fermentation of formate, certain hydroxy-acids, pyruvic acid, primary alcohols (methanol, ethanol, propanol and butanol), glycerol and methyl compounds. With primary alcohols there was a stoichiometric relationship between methane production and the oxidation of the alcohols to the corresponding acids.
The fermentation of rhamnose and 1,2-propanediol was studied in detail. With both compounds there was a temporary accumulation of lactic acid and a continuous net production of propionic acid. The initial rate of acetate production was rapid with rhamnose but decreased subsequently, whereas propionate continued to increase. With propanediol the net rate of production of acetate was slow at first and then increased. There was no increase in the production of butyric acid with either rhamnose or propanediol, and the endogenous methane production was inhibited by 20–40%. There was evidence for the formation of an unidentified compound during fermentation of rhamnose and propanediol.