673. Bacteriology of Cheddar cheese: A study of starter organisms in manufacture and maturing

1. The trends of starter bacteria population during the manufacture and maturing of Cheddar cheese have been investigated. Fourteen strains consisting of Str. lactis, Str. diacetilactis and Str. cremoris have been studied. 2. Physiological and morphological characteristics of the fourteen strains were examined. 3. Population studies during manufacture showed that the three species of starter organism attain quite different maximum populations and at different stages of the cheesemaking process. Str. lactis (4500 millions/g.) and Str. diacetilactis (2900 millions/g.) reached their maximum half way through Cheddaring, whereas Str. cremoris (960 millions/g.) reached its maximum at milling. 4. Str. lactis was shown to maintain its maximum population until the cheese left the press, whereas Str. diacetilactis and Str. cremoris steadily declined after reaching their maximum. 5. Counts of the different starter cultures used showed considerable variation between and within strains, particularly in the case of Str. cremoris. 6. No relationship was shown to exist between acidity development and starter populations developed. 7. The study of cell distribution in the cheese curd has shown that whereas Str. lactis and Str. diacetilactis gave an even scattering of diplococci, Str. cremoris showed colony formation. 8. Str. lactis strains maintained a high but declining population during maturing of the cheese, the starter beginning to die out gradually after 8 weeks. Str. diacetilactis showed similar trends but at lower populations levels. Str. cremoris, on the other hand, gave much lower populations, the starter dying out rapidly after 2 weeks, and virtually disappearing at 8 weeks. 9. Persistence of starter bacteria in the cheese appears to be correlated with salt tolerance and chain length. 10. Starter bacteria isolated from the cheese made with Str. lactis have shown a low proportion of slow acid-producing types in contrast to a high proportion found with Str. cremoris. 11. The non-starter bacteria in the cheese were found to consist on the average of 30% micrococci and 70% lactobacilli. Negligible numbers of other genera were isolated.