Foam is an important aspect of coffee preparation, and it determines, or validate quality in some coffee drinks.
Coffee beans contain carbon dioxide immediately after roasting. The degassing starts right after roasting and is the process of seeping out the gasses from the beans. A lot of the CO2 leaves the beans in the first 24 hours after roasting, that is about 40%. Lighter roasts degass slower, whereas dark roasts degass faster. Gasses in the coffee beans is a sign of a freshly roasted coffee.
Filtration is commonly the mechanical or physical operation which is used for the separation of solids from fluids (liquids or gases) by interposing a medium through which only the fluid can pass. Oversize solids in the fluid are retained, but the separation is not complete; solids will be contaminated with some fluid and filtrate will contain fine particles (depending on the pore size and filter thickness).
A coffee filter is a utensil used during coffee brewing, for filtering coffee grounds from the brewed liquid. It is usually made of disposable paper with filaments approximately 20 micrometres wide. The fine paper screen only allows to pass through particles less than approximately 15 micrometres. This enables it to trap the coffee grounds that are bigger. The small water particles and the fines can flow through, resulting in clear coffee.
Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants, as well as enhancing the reward memory of pollinators.
Arabic coffee is a general name that refers to the two main ways coffee is prepared in many Arab countries: Turkish-style, and Saudi Coffee. The Turkish coffee brewing method is common in the Levant, but brewed without the addition of sugar. Cardamom is often added, or it is served plain قهوة سادة qahwah sādah (lit. “plain coffee“).
A decanter is a vessel that is used to hold the decantation of a liquid which may contain sediment. Decanters are normally used as serving vessels for wine. Decanters vary in shape and design. They are usually made of an inert material and will hold at least one standard bottle of wine (0.75 litre). A similar kind of vessel, the carafe /kəˈræf/, is used for serving wine as well as other drinks, but is not supplied with a stopper.
Espresso crema is a brown, foamy layer on top of the brewed coffee. Crema is a mix of gas bubbles, and emulsified fats, which are the signature of a good espresso. The perfect crema is a reddish-brown foam, with tiny bubbles. If the bubbles are too big, the shot was incorrectly extracted. If the colour is too light is an under-extracted shot, and if it’s too dark, the shot is over-extracted.
Ristretto is a short shot of espresso coffee made with the normal amount of ground coffee but extracted with about half the amount of water. Traditionally, a ristretto is extracted using the same amount of coffee grounds and water as a normale, but reducing the time to brew it. The result is a concentrated espresso with a different flavor and taste profile, and slightly lower caffeine content.