- Much is done to keep numbers of bacteria in milk as low as possible; the milking equipment is sterilised, the cow’s udders are washed before milking and most milk is cooled rapidly to slow the growth of bacteria. It is then pasteurised.
- If bacteria have everything they need (food, oxygen and warmth) they can grow into a colony of millions in a few days.
- We say the population of bacteria grows exponentially. In the right conditions bacteria can divide by binary fission every 20 minutes.
- The number of bacteria in a sample can be measured using resazurin dye which turns blue in high levels of oxygen. As the concentration of oxygen decreases it changes to lilac, mauve then pink and eventually colourless. The more bacteria there are, the more quickly oxygen levels fall.