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Ristretto is a very short shot of espresso coffee. Originally this meant pulling a hand press (shown at right) faster than usual using the same amount of water as a regular shot of espresso. Since the water came in contact with the grinds for a much shorter time the caffeine is extracted in reduced ratio to the flavorful coffee oils. This is counterintuitive since caffeine is far more soluble than coffee oils. The resultant shot could be described as bolder, fuller, with more body and less bitterness. All of these flavors are usually attributed to espresso in general, but are more pronounced in ristretto. Today, with the hand press out of favor and modern automated machines generally less controllable, ristretto usually just means less water; a double espresso shot is typically around 60 ml (2 fl oz), while a double ristretto is typically 25-30 mls (1–1.5 fl oz). One shot of espresso is 8grams of coffee in 30 ml of water, while one shot of ristretto is normally 8grams of coffee in 15ml of water, making ristretto very strong.
One modern method of pulling a ristretto shot is to grind the coffee finer than that used for normal espresso, and pull the shot for the same amount of time as a normal shot. The smaller spaces between the particles of finer-ground coffee allow less water to pass through, resulting in a shorter shot. However, this can also lead to a gritty taste, if the coffee is so fine so as to allow the insoluble components to pass through the filter-basket. This is often a problem in poorer grinders, where the grind is not as even.
Another modern method for pulling a ristretto is to simply stop the extraction early, so less water has time to pass through the ground coffee. This produces a slightly different taste than the fine-grinding, equal-time method, and is often preferred in fast-paced cafes because it does not require the barista to change the settings on the coffee grinder.
A third modern method, that serves as a compromise between the previous two, is to prepare the shot without adjusting the grind but to use the tamp more firmly. The firmer tamp will compact the grinds in the filter basket allowing for a shot time comparable to a regular espresso. This method has the added benefit that adjusting the coffee grinder is not necessary while keeping much of the body and flavor of the fine-grinding, equal-time method.
As the amount of water is increased or decreased relative to a normal shot, the composition of the shot changes, because not all components of coffee dissolve at the same rate. For this reason, an excessively long or short shot will not contain the same ratio of components that a normal shot contains. Therefore, a ristretto is not simply twice as strong as a regular shot, nor is a lungo simply half the strength.