Bacteria in fermented milk products, like lactobacilli and lactococci produce lactic acid in anaerobic environments. Therefor I chose a bottle with tight cap for the expeiment. The tolerated temperature range vary a lot between different species and subspecies. Lactococcus lactis subsp. cremoris has a temperature growth range 10°–42°C (50°–108° F), and seems be to a good choice for room temperature. The bacteria along with others can be found in crème fraîche. By the use of crème fraîche in my experiment I ensure that at least one species of bacteria grow. All my equipment were decontaminated by washing and drying, thus not sterilezed. The procedure was as follows, in a cup I stirred together:
- 15 ml non-fat milk powder
- 150 ml water
- 15 ml crème fraîche
Then I filled the bottle with the mixture, screwed on the cap and put it into my thigh pocket. I kept it there in order for the liquid to be shaken. In step with the increasing amount of lactic acid, more and more milk casein coagulated and the milk became thicker and thicker. Now and then I checked the consistency by turning the bottle up-side-down while watching how fast the air bubble moved.
After 18 hours the fermented milk appeared to be done and I opened the bottle. The top layer of the milk was very thick. Beneath this layer the milk hadn't become that very thick. It smelled a combination of yogurt and milk powder.
I poured up the fermented milk in a cup, blended and had it for snack. The image below on the left shows the stripes of the coagulated casein on the wall of the cup. It tasted similar to yogurt. Even though it was tasty, it could have been much tastier if it would have contained fat. Of course it's never guaranteed risk free to eat a product from an experiment. No gastro-intestinal symptoms were detected, that could be affiliated with the consumption of the fermented milk. The experiment shows that media based on milk powder can work very well. This knowledge will probably be very useful in future experiments.
References
- Wikipedia article about crème fraîche
- Toqeer Ahmed, Rashida Kanwal and Najma Ayub; Influence of Temperature on Growth Pattern of Lactococcus lactis, Streptococcus cremoris and Lactobacillus acidophilus Isolated from Camel Milk
- http://aem.asm.org/content/64/5/1950.full
- http://www.dairyconnection.com/Page3.html
- http://en.wikipedia.org/wiki/Lactic_acid_fermentation
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