Volatility (chemistry)

In chemistry and physics, volatility is the tendency of a substance to vaporize. Volatility is directly related to a substance’s vapor pressure. At a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with a lower vapor pressure.

In specialty coffee, volatility is particularly important because coffee taste and aroma are influenced by certain compounds that are relatively volatile. The more volatile the compound is the faster it will vaporize. This is why the coffee brewing temperature is so important; it allows proper and fast extraction of nonvolatile components, while preserving the volatile ones. Espresso extraction is a few degrees lower than drip coffee. Pressure helps extract more TDS at a lower temperature, while preserving volatile components. This is why various compounds such as coffee oils and the compounds cafestol and kahweol are present in espresso brewed coffee but are absent in filter brewed coffee.

Cold brew coffee is a brewing process that uses no heat at all and instead relies on time for extraction. This makes the brewed beverage much less volatile. It is much slower to oxidize and to spoil. Various volatile compounds from the coffee bean can be found in cold brew coffee that aren’t present in hot coffee because the higher brewing temperature has caused these compounds to vaporize.