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Single strains of bacteria isolated from the surface of commercial Tilsit cheeses were screened for their ability to produce typical Tilsit flavour and colour and for fast growth in milk. Three milk based model systems were developed for screening. Shake liquid milk cultures were suitable to determine production of colour and volatile flavour compounds. Milk agar plates were used to study synergistic and antagonistic effects between isolates. With mini cheeses in centrifuge bottles, cheese conditions were simulated under sterile conditions. Volatile aroma production and pigmentation of the surface flora were studied with this system. Additional growth studies in other growth media with various combinations of strains revealed some of the possible roles of surface bacteria. Brevibacfen'um linens promoted growth of yellow coryneform bacteria. A pigmented Arthrobacter strain was responsible for the production of a yellow coloured watersoluble pigment, a precursor for the typical red-brown colour of Tilsit cheese. In mixed culture with pigmented or non-pigmented strains of B. linens, the yellow colour turned into red-brown. A proteolytic Staphylococcus strain seemed to be important for the initiation of surface starter growth. Staphylococci showed fast growth at pH 5.5 and below. They also promoted growth of the yellow Arthrobacter strain.Based on these results, a defined surface starter was developed consisting of 5 strains. The yeast Debaryomyces hansenii was used for deacidification of the cheese rind. A combination of a non-pigmented, proteolytic B. linens, a yellow Arhrobacter strain, a cream-coloured coryneform bacterium, and a proteolytic Staphylococcus sciuri were used for cheese ripening. Experimental cheeses were produced on a 10 kg scale. The defined starter grew fast on the cheese surfaces, and produced the typical taste and flavour and colour of Tilsit cheese.

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