10 ml samples of milk from each participant were placed in 13 ml polypropylene tubes, which were then submerged (until the water reached a level of approximately 2 centimetres over the level of milk) in a shaking water bath that was preheated to 62.5 °C. The water did not touch the caps, to avoid microbiological contamination of milk. All tubes in the batch con- tained the same amount of milk.