![]() Ideally, you will be pulling between 1.5 and 1.75 ounces of espresso from your double portafilter. However, there should not be large yellow streaks in the crema (blonding which is a tell-tale sign of over-extraction and channeling). This crema should not be a pale brown, or a yellowish color, but like the above example should be a deep brown with speckling of darker brown or black in the crema itself. ![]() This means at the end of pulling a shot of Full Cycle or Ernesto's, you should be seeing at least a half inch of crema on top of the espresso. Ideally, we are looking for espresso with good, thick crema. In order to dial in our espresso by sight, it is important to look for a few benchmarks in the appearance of the crema, the volume of the liquid, and the amount of time it takes to pull that volume of liquid. These help form the dark speckling on a good espresso. Finally, actual bits of the coffee's cellulose and lignin fiber will be stripped off the grounds and held in solution (called fines). Additionally, the non-water-soluble compounds, like oils, held within the coffee grounds will begin to be emulsified in the hot water. This list includes mineral salts, organic acids, volatile aromatic compounds, sugars, caffeine, sugar browning byproducts, alcohols, esters, and many many more. In addition to CO2, a number of different organic compounds will begin to dissolve and be held in solution in the beverage. This is why it is important to let the coffee rest a few days so it can de-gas, ensuring that there will not be an over-abundance of CO2 in the solution (we let ours rest 5 days). This gas will begin to dissolve and be held in solution within the espresso. The first of these compounds to be removed by the hot water will be carbon dioxide. This will result in a very intense flavor which many will identify as being bitter, woody, and acrid.ĭuring the process of extraction, as with most brewing processes, a series of compounds will be removed from the ground coffee. ![]() On the other hand, sometimes the espresso is ground too finely and the water will not be able to pass through quickly enough, and the shot will pull slowly causing over-extraction. This under-extraction causes a weak shot, with a sour/salty flavor in the espresso. Often, espressos will be ground too coarsely and the water will flow through too quickly leaving the grounds under-extracted. Another common problem deals with how to dial in the shot. What this leads to is over-extraction along the grounds near the channel, and under-extraction for the rest of the puck. As I often tell people during training, water will always find the spot of least resistance and will exploit it. This is where a crack, hole, place of differing density, or weak spot causes water to run more quickly through those grounds than it does the rest of the puck. One of the most common issues in espresso extraction is called channeling. Espresso extraction occurs when water which is around 200-202 F is pushed through a compact bed of coffee (the puck) at 9 bars of atmospheric pressure, which equates to 9 times the atmospheric pressure or roughly 140 psi, and a 58 mm basket is 4.1sq in of area making it a total of 574 lbs of force (also why you can never out-tamp a professional espresso machine)! Because of this high pressure, certain issues can occur during the brewing process that can ruin the flavor of the shot. The difference with espresso is that this reaction occurs under pressure. As with most brewing methods, there are a series of reactions that occur when the hot water comes in contact with the coffee grounds and begins to extract the solids, liquids, and gasses which create the drink we know as coffee.
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