Reaction of Streptococcus thermophilus to Stress

The effect of low pH on the survival of S. thermophilus in liquid cultures was studied. Results showed that the bacteria do not live more than a week at 37°C when grown in milk. Survival can be prolonged by growing them in diluted milk or preferably in M17 containing low concentrations of lactose. It would probably advantageous to supply cheese manufacturers in Switzerland with cultures at a pH close to 5.9 in order to prolong their shelf life.