How Espresso is Made Using Espresso Machine?
Moltio Focus Super automatic espresso machine HD8767 47 from Espresso Machine, source:usa.philips.com
The Espresso Machine’s Role
The espresso machine’s task is to deliver water to the grounds in a predetermined pattern of temperatures and pressures. These patterns are known as tempemture profiles and pressure profiles. A quality espresso machine should be able to produce consistent temperature and pressure profiles every shot, even under heavy use.
The Phases of Espresso Percolation
- Preirifusion. Once the pump is engaged, the first phase of espresso percola tion is a brief, low-pressure preinfusion. (Some machines skip this step and go directly to the second phase.) During preinfusion the grounds are wetted by a slow, low-pressure flow, which allows the coffee bed to reorganize itself and create a more even flow resistance.
- Pressure increase. In the second phase, the pressure increases, compacting the coffee bed and increasing the flow rate. Machines without a preinfusion cycle start at this phase; such machines can make great espresso, but they are more fickle and less “forgiving” of inconsistencies on the part of the barista.
- Extraction. In the third phase, extraction begins, and espresso flows from the filter basket. Extraction is primarily accomplished by the washing, or erosion, of solids from the surfaces of the ground coffee particles by the brewing water.
The eluted extract starts out relatively dark and concentrated with solids and be comes more dilute and yellow as extraction progresses. Throughout extraction, solids are removed from the coffee bed in a mostly top-down fashion; solids are preferentially removed from the upper layers of grounds. As solids are transported through the coffee bed, some settle lower in the bed, some get deposited in the com pact layer, and others get extracted from the bed into the cup.
Brew Strength and Yield: Espresso
The brew strength of an espresso refers to its concentration of solids, which is be tween 20-60 mg/ml when using traditional Italian standards. The solids yield of an espresso is the percentage of mass removed from the grounds during extrac tion; solids make up about 90% of the extracted material in an espresso. Please note: when discussing espresso it is common to refer to solids concentration and solids yield, whereas when discussing drip coffee it is more appropriate to focus on solubles concentration and solubles yield.
Brew strength and yield have no direct relationship. For instance, using higher water temperature simultaneously increases brew strength and yield, while run ning extra water through a bed of grounds decreases strength and increases yield.