The production of a frozen concentrated cheese starter by batch culture fermentation of a mixed species cheese starter culture consisting of Streptococcus cremoris and Streptococcus diacetilactis was investigated. A response surface analysis to optimize growth conditions was made using 20% NaOH or 20% NH4OH as neutralizers and pH and temperature as variables. The yield of cell mass was about two-fold higher using NH4OH as the neutralizer. The optimal growth conditions for the latter were pH 6.1 to 6.5 and 24 to 27 C. Optimal balance of species of one S. diacetilactis per six S. cremoris cells was observed from a growth pH of 6.1 to 6.4 and temperatures of 23 to 26 C using NH4OH. A pH of 6.2 to 6.5 and temperature of 25 to 27 C yielded cells of highest acid-producing ability when NH4OH was the neutralizer. Cultures grown at 25 C using NH4OH were also more resistant to freezing than NaOH neutralized cultures. Glycerol was the only cryoprotective agent examined which protected the culture during freezing and frozen storage. Lactose and malic acid appeared to have a destructive effect on the starter concentrate during frozen storage. Conditions of growth and type of cryoprotective agent affected each species individually. Gouda cheese prepared from a frozen concentrate was equivalent in quality to that prepared from a conventional bulk starter culture.

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Author notes

1Scientific Journal Series Paper No. 8820 Minnesota Agricultural Experiment Station, St. Paul, Minnesota 55108.

2This work was taken from a thesis submitted by J. D. Efstathiou to the faculty of the Graduate School of the University of Minnesota in partial fulfillment of the requirements for the degree of Master of Science.