318. The effect of acidity on the production of diacetyl by betacocci in milk

1. The diacetyl production of betacocci isolated from starters, cheese and rye-grass was investigated at pR values ranging from 5.5 to 44. The betacocci produced diacetyl and subsequently partially or wholly destroyed it. 2. There was a considerable variation in the amount of diacetyl produced by the different strains of betacocci. Capacity to produce diacetyl could not be correlated with any other property of the organisms. 3. The rate of growth of the organisms was progressively slower the lower the pH, but at least as much diacetyl was eventually formed at low pK values as at high pH. values. The results showed that there was an alteration in the metabolism of the organisms, the diacetyl-producing power per unit cell increasing with decreasing pH. 4. The results found enable an explanation of the rapid production of diacetyl in mixed starters to be offered.