This paper discusses causes of flavor deterioration, i.e. a loss of freshness, in foods during storage. Freshness may be lost for several reasons including: a loss of specific aroma compounds that are 'fresh' in character; the loss of characterizing aroma compounds (e.g. bready, beany, etc); or the masking of a fresh flavor due to the development of off-flavors. The hypothesis that "fresh" aroma compounds are lost during storage may be true but is difficult to prove since there are few, if any, aroma compounds identified to date that are characterized as being "fresh". The validity of each of these hypotheses is discussed and evidence from the literature is presented in support of the discussion.