Going Large: Making Two and Four Drinks at a Time
The quantity of foam in a cup changes the flavour intensity of a drink considerably. We know from research by Nestle on the subject of crema that the bubbles contain a considerable amount of aromatic gases which are released into the mouth as we swallow (Barronet et al 2012). The dilution and mixing of intense coffee aromas with very mild milk aromas accounts for the reduction in coffee flavour intensity in milk drinks.
One means of achieving a more concentrated coffee flavour is to increase your milk foam aeration level. The more volume taken up in a cup by foam, the higher the concentration of coffee solids in the milk. For example, a 50% air fraction will deliver a stronger coffee flavour than a 20% air fraction.
The drainage process in steamed milk can take minutes to finish, but it begins immediately. The milk at the bottom of a freshly steamed pitcher of milk will always contain fewer air bubbles than the milk at the top. This means that even if you are working very quickly, you shouldn’t just pour the top half of your pitcher of milk into the first drink and the bottom half into your next drink — you need a strategy to distribute the foam evenly, in the least-time-consuming manner possible, in order to efficiently deliver consistent coffee flavour intensity. If you do pour immediately without taking this into account, the first drink will always have more foam. One strategy to avoid this is to split your milk into two separate pitchers, using the ‘Four Quarters Method’.
The Four Quarters Method
The Four Quarters Method is the one way to achieve even foam distribution. The goal is to mix the foamiest part of your milk (the top quarter) with the least foamy part (the bottom quarter.) The system works on the assumption that the milk in the second-highest quarter and the second-lowest quarter will be similar in air content to the milk combined from the top and bottom quarters.