Acid production in milk by starter cultures—The effect of peptone and other stimulatory substances

The rate of acid production by a slow variant ofStreptococcus cremorisin milk was raised to that of the fast parent strain when peptone or acid hydrolysed peptone were added. Lactose utilization was similarly affected. However, the stimulation took place without any change in the rate of growth. Other sources of available nitrogen gave similar results. It is concluded that the change from a fast to a slow culture which occurs on continued transfer is due to the loss of ability to utilize the nitrogen compounds of milk.