Why does milk work with coffee? Dairy products are classic enhancers of some of the flavour notes found in coffee, and milk and they also softens bitterness. The three components of milk that have an impact on its flavour and texture are sugar (lactose), protein and fat.
The quantity and quality of the foam you create in your milk is dependent on the techniques you employ to incorporate the air into the milk as well as the type of milk you use. The process of adding milk to air is called foaming or stretching because it increases the volume of the milk.
Bubbles in milk can range in size enormously but if you foam well the bubbles will be so incorporated into the milk that they won’t even be apparent as bubbles. Microfoam is the term used to describe frothed milk where the bubbles are so small and numerous that they can’t even be seen, though they can be sensed on the palate as a lovely velvety texture. The milk will appear thicker and creamier
Creating stable milk foam involves a careful reaction between the desirable foaming properties of milk proteins with the destabilising properties of milk fat.
The taste impact of lactose One of the things many baristas get wrong (often as a result of customer demand) is the temperature to which they heat the milk - too hot and its flavours alter.
Lactose doesn’t taste particularly sweet but when excessively heated it breaks down in to its composite sugars, glucose and galactose, making it taste sweeter. Heating milk over 70˚C also “denatures” the proteins giving you the characteristic eggy custardy flavour of cooked milk.