More on squeezing and storing citrus juice. → July 24, 2013 by Kevin Upthegrove One possible explanation as to why a slight (4-hour) aging on fresh hand-squeezed juice may be preferable to just-squeezed. Enzymatic Bittering. My favorite explanation for the decrease in tartness of aged lime juice. Bartender Stephen Shellenberger explained to me that all citrus fruits contain an enzyme that will produce the bitter compound limonin in the hours immediately after juicing. As we’ve covered before, a very small amount of bitter flavor can mildly suppress sourness. Science. Part of successful cocktails.