A reddish-brown, frothy substance, which settles on top of a shot or cup of espresso, giving it extra flavor and fragrance, is known as crema. A well formed crema is an indication of a well-made shot of espresso. It signifies the good quality coffee grounds used to make the coffee and the skilled procedure behind making it. The quantity of crema is usually one-tenth of the quantity of the espresso. How good the crema formation takes place usually depends on factors such as extraction of the beans, coarseness of the beans, size, and roasting of the beans and more. The high pressure of hot water, striking the coffee beans, causing the water to emulsify the oils present in the coffee beans, results in the formation of a perfect layer of crema on top of a shot of espresso. The process usually takes 20 to 30 seconds.