A coffee beverage, which is very popular and favorite drink, is usually produced by blending a roasted coffee bean extract therein. Taste and flavor of a coffee beverage include bitterness, sweetness, acidity, body, rich taste and miscellaneous unpleasant taste or the like. These tastes and flavors are characterized by type of green coffee beans and a roasting method thereof for use in producing a roasted coffee bean extract.
In roasting green coffee beans, many aroma components, which are originally absent in green coffee beans, are produced by a heat treatment. For example, chlorogenic acids are known to be converted into chlorogenic acid lactones at the time of roasting. The chlorogenic acid lactones are substances giving bitterness. Since a threshold of chlorogenic acid lactones is low, one senses strong bitterness even if chlorogenic acid lactones are only slightly present.
Then, to reduce the content of chlorogenic acid lactones giving bitterness various attempts have been made and reported. As a method thereof, for example, Patent Document 1 proposes a method for converting chlorogenic acid lactones to chlorogenic acids by treating a roasted coffee bean extract with alkali; and Patent Document 2 proposes a method for reducing the content of chlorogenic acid lactones by treating a roasted coffee bean extract with an enzyme to hydrolyze the chlorogenic acid lactones or by bringing a roasted coffee bean extract into contact with a solid adsorbent.