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Cider Digest #0720
Subject: Cider Digest #720, 25 January 1998
From: cider-request@talisman.com
Cider Digest #720 25 January 1998
Forum for Discussion of Cider Issues
Dick Dunn, Digest Janitor
Contents:
Cranberry juice fermentation (Andrew Lea)
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Subject: Cranberry juice fermentation
From: Andrew Lea <andrew_lea@compuserve.com>
Date: Sat, 24 Jan 1998 18:21:41 -0500
There have been several mentions of cranberry juice in the Digest over the
past year, from people who are blending it with cider and either can or
cannot get it to ferment! The received wisdom is that cranberry juice
contains benzoic acid at say 100 ppm, and therefore doesn't ferment because
it's inhibitory to the yeast - however, several contributors to these pages
have reported that it DOES!
Recently I've been doing some professional scientific work on cranberries
and I think I can now explain the mystery. It turns out that the benzoic
acid in fresh cranberries is mostly tied up in the berries as a sugar ester
called 'vacciniin'. This ester is NOT inhibitory to yeast - however, the
benzoic acid which is liberated from it IS. The liberation is effected by
a glucosidase enzyme, so the key is the activity of this enzyme.
If the cranberry juice is prepared and pasteurised immediately, then the
enzyme doesn't have time to work and little free benzoic acid is produced.
If the juice is allowed to stand for some time (maybe only a few minutes),
the enzyme will start to generate benzoic acid. This is especially the
case if frozen cranberries are used, because the act of freezing disrupts
the cell structure, thus bringing both enzyme and substrate into intimate
contact. As the fruit thaws, enzymic degradation in the ruptured fruit can
occur very quickly, so that by the time the fruit is back up to room
temperature ALL the vacciniin is converted to free benzoic acid - we found
over 1000 ppm in some samples of thawed fruit. That juice will then be
very inhibitory to yeast.
Hence the amount of free benzoic acid in a cranberry juice (and hence its
inhibitory powers) depends on its processing history! It will also depend
on whether or not additional enzymes have been used during commercial juice
preparation (as they often are). It seems if you want to be sure the
cranberry juice will ferment, the best route is likely to be to take fresh
cranberries and cook them quickly yourself to inactivate the enzyme -
although even then it may be impossible to avoid the presence of enough
free benzoic acid to have some inhibitory properties.
Andrew Lea, nr Oxford, UK
http://ourworld.compuserve.com/homepages/andrew_lea
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End of Cider Digest #720
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