A buffered growth medium was developed that sustained a significantly greater concentration of various strains of Streptococcus lactis and Streptococcus cremoris than did milk. The active buffering ingredients of this medium were magnesium hydroxide, ammonium and sodium salts of phosphate and citrate. This medium was entitled Lactic Culture Buffered Growth medium (LABGRO) and possessed about 8 times the buffering strength between pH 6.6 and 5.1. Significant differences in growth and acid production rates were noted among Prt+ and Prt- lactic strains evaluated. Also noted were significant differences in cellular acid production rates. The two Prt- strains having the slowest growth rate in milk were selected as test strains to evaluate stimulants. Three strains of Kluyveromyces fragilis were aerobically propagated in whey medium and afterwards subjected to autolysis conditions. Whey protein and casein were added to some yeast samples prior to initiation of autolysis. To some of these latter samples, pepsin was added. After autolysis the yeast and yeast-protein samples were dried and their stimulatory properties for lactic culture propagation were evaluated with a test strain and LABGRO medium. No product was found to be as stimulatory as a control commercial yeast autolysate. Yeast-protein samples with added pepsin were markedly more stimulatory than the other samples. The whey-derived yeast extract significantly improved the lactic culture growth stimulating properties of protein hydrolysates.