Water
Activity of Foods
Water activity refers
to the availability of water in a food or beverage and represents
the amount of water that is available to microorganisms. Pure
water has an aw of 1.00.
Most microorganisms
grow well at 0.91 to 0.99. Clostridium botulinum will grow
and produce deadly botulism toxin if the pH is above 4.6 and
the water activity is above 0.85.
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aw
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Microorganisms grow at this aw
and above
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Food examples
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0.95
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Pseudomonas,
Escherichia, Proteus, Shigella, Klebsiella,
Bacillus, Clostridium perfringens, some yeasts
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Highly
perishable foods (fresh and canned fruits, vegetables, meat, fish),
milk, cooked sausages, breads, foods with up to 4 oz sucrose or
7% NaCl
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0.91
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Salmonella, Vibrio parabaemolyticus, C. botulinum,
Lactobacillus, some molds
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Some
cheese (Cheddar, Swiss, Provolone), cured meat, fruit juice concentrates
with 55% sucrose or 12% NaCl
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0.87
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Many
yeasts, Candida, Torulopsis, Hansenula micrococcus
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Fermented
sausage, sponge cakes, dry cheese, margarine, foods with 65% sucrose
or 15% NaCl
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0.80
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Most
molds, most Saccharomyces spp., Debaryomyces, Staphylococcus
aureus
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Most
fruit juice concentrates, condensed milk, syrup, flour, high-sugar
cakes, pulses containing 15-17% moisture
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0.75
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Most
halophilic bacteria, Mycotoxigenic aspergilli
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Jam,
marmalade, glace fruits, marzipan, marshmallows
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0.65
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Xerophilic
molds, Saccharomyces bisporus
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Rolled
oats with 10% moisture, jelly, molasses, nuts
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0.60
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Osmophilic
yeasts, few molds
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Dried
fruits with 15-20% moisture, caramel, toffee, honey
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0.50
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No
microbial proliferation
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Noodles
with 12% moisture, spices with 10% moisture
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0.40
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Whole
egg powder with 5% moisture
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0.30
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Cookies,
crackers, bread crusts with 3-5% moisture
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0.03
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Whole
milk powder with 2-3% moisture, dehydrated soups
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