The condition that has been chosen as the independent variable is acidity, as it is simple to be held at a constant value throughout the investigation, unlike many of the other factor which will likely fluctuate.

A risk assessment must be undertaken prior to the experiment, as the chemicals that will be used to alter the pH levels can be harmful to people

All other conditions that may affect the growth of microbes in yoghurt should be kept constant throughout all of the trials

Any things that are added to the yoghurt starter such as flavours, colours or fruits may affect the ways in which the bacteria grows.

Bacteria ferments the milk into yoghurt by producing lactic acid