Basic knowledge of Fine Coffee about some commonly used words in extraction

Blonding: Describes the process by which the effluent changes from a dark brown with tiger stripes to a uniform pale yellow. This usually occurs in the last 1/3 of the paragraph, indicating that the extraction operation can be completed. The over-yellowing part of the espresso has a weak taste and little aroma. If it lasts too long, it will dilute the alcohol and no longer be a pleasant taste sensation.

Channeling: Water flows rapidly through cracks in the coffee cake, resulting in a thin, under-extracted espresso. When this happens, a sudden yellow streak is often seen in the coffee stream; sometimes the channeling effect leaves a pencil-lead-sized hole in the coffee cake.

Coffee oil (Crema): is a signal confirming proper espresso making (on coffee machines where coffee oil is not forced to be produced), the result of various gases-air and carbon dioxide-being distributed in water under high pressure. The liquid also includes emulsified oil. It forms a dark golden-brown frothy substance on the surface of the espresso coffee.

Golden rule: A common term used to describe the ideal time and volume for espresso extraction. The Instituto Nationale Espresso Italiano provides a practical definition of the ideal espresso characteristics, although these parameters are more like "golden rules" than mandatory regulations. A simple definition is: use about 16-18 grams of coffee to produce a 60 ml double in 22 - 27 seconds (counting from the outflow of coffee).

Over-extraction: Excessive coffee solids are extracted, producing a strong, pungent aroma. Visually, the coffee is low in volume, and the coffee oil is a thin layer of black. The dark circles around the rim of the cup are another typical indicator of over-extraction or extraction water temperatures that are too high.

Pre-infusion: The act of pre-impregnating coffee powder inside an espresso machine before it actually begins to extract coffee. Some coffee machines are achieved by a pump; the pump works for 1 to 2 seconds and stops for 1 to 2 seconds. Then start again to extract coffee. Fully automatic machines and some automatic machines use this method. Another type called "natural" or progressive pre-impregnation is the machine equipped with the E61 outlet head. After the pump is started, the second chamber must be filled before the pressure is fully applied to the coffee cake. The coffee powder is allowed to soak for 3 to 7 seconds before pressure builds up. This type of prepreg is more popular. There is a truckload of claims explaining that progressive pre-wetting improves coffee extraction.

Tiger stripes and mottled spots: the main visual cue for good extraction. Tiger spots are formed by contrasting dark and light coffee oils in the coffee stream; ideally, they appear at the beginning of the coffee stream and last until the end. "Mottled spots" are the appearance of a good extract in the cup; refers to small dark brown spots and reddish brown markings that form on the surface of coffee oil.

Underextraction: Insufficient extraction of coffee solids, resulting in a weak, bland aroma. Visually, it is a fast, large-volume extraction, and the coffee oil is evenly pale yellow.