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