Rotronic HP23-AW-A User Manual
Solutions for measurement
and monitoring of
water activity
Avoid stale surprises
INTRODUCTION TO WATER ACTIVITY
Water activity is often called “free” or “non-chemically bound” water in foods and other products. Although these terms are
easier to understand, they do not define all aspects of the concept of water activity.
The correct definition
“Water activity – a measure for the energy status of the water in a system” specifies
the relationship between the water vapor pressure of a product and the saturation
pressure of pur e water at the same temper ature. It is state d in “aw” in the range 0…1 aw
and is an important indicator for product quality in the industrial production of, for
example, plastics. The determination of water activity is also very important in the
food, tobacco, pharmaceutical and cosmetics industries. Water activity should not
be confused with the water content – the “chemically bound” water – of a product.
Tex ture Taste Color Nutritional value Shelf life
Interested?
Scan the QR code
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video or visit
www.rotronic.com/aw
Water activity influences the following properties of a product:
• microbiological stability
• chemical stability
• enzymatic stability
• color, taste and nutritional value
• protein and vitamin content
• stability of the composition
• shelf life
• storage and packaging
• solubility and texture
Contents
Introduction to water activity 2
Applications 3
Product overview 4
Products 5 - 8
Software 9
Calibration 10
Theory 11
Rotronic worldwide 12
2
Rotronic – Water activity measurement
APPLICATIONS
All forms of life depend on water. Water activity indicates the amount of water which is biologically available to microorganisms. Each
species of microorganism (bacteria, yeast, mold…) has a minimum water activity value below which growth is no longer possible.
Water activity plays an important role for product quality in
various fields, including:
• Industrial manufacturing
• Food industr y
• Pharmaceutical and Cosmetics industry
• Tobacco industry
• Seed storage
The US Food and Drug Administration (FDA) has adopted the concept of water activity for establishing limits beyond which certain
types of foods are considered susceptible to mold and bacteria and have established the following table indicating which process
control procedure can be used. It specifies pathogens of concern and control methods for various product categories (including
examples of foods that may need to be evaluated for time/temperature control needs for safety).
Product category (examples of
possible foods for evaluation)
Meats and poultry
(fermented sausage)
Fish and seafood (smoked fish) Vibrio vulnificus, Vibrio parahaemolyticus, Vi-
Cereal grains and related products
(fresh pasta, foccacia bread)
Pathogens of concern Types of process control 1
Clostridium botulinum5 and Clostridium
perfringens, Salmonella spp., enterohemmorr-
hagic Escherichia coli, Camplylobacter...
brio cholerae, C. botulinum5, L. monocytoge-
nes, Salmonella spp., Shigella spp., S. aureus
Salmonella spp., S. aureus, B. cereus, C.
botulinum5
Water activity Contaminant
aw = 0.91...0.95 Many bacteria
aw = 0.88 Many yeasts
aw = 0.80 Many mildews
aw = 0.75 Halophile bacteria
aw = 0.70 Osmiophile yeasts
aw = 0.65 Xerophile mildew
(alone and in combination)
Time/temperature, pH, aw, preserva-
tives, moisture protein ratio, fermen-
tation, heat processing
Time/temperature, harvest site control, fermentation, pH, aw, water-pha-
se salt, preservatives, drying, salting
Cooking, aw, pH, preservatives, time/
temperature
The water activity (aw) in foods can be controlled by using various additives (humectants), using satisfactor y packaging materials
and by maintaining favorable maturation and storage conditions. Should too much water be available, there is a risk of microbial
growth and water migration. Food manufacturers today must prove to the FDA that the water activity of a product has been re-
duced sufficiently so that bacteria can’t grow.
The water activity (aw) of a product will always tr y to reach equilibrium with the surrounding atmosphere. Water will migrate inside
the product from regions with a high aw value to the regions of low aw. Water will migrate until equilibrium is reached! Therefore
it is crucial to measure the water activity level of all components of a product as well as the ambient atmosphere to ensure the
quality of a product. Water migration may cause the following issues: clumping, change of texture, reduced shelf life.
Water activity data may be used when deciding whether a product requires testing or not. The United States Pharmacopeia (USP)
<1112> states that pharmaceutical drug products with water activities well below 0.75 would be excellent candidates for reduced
microbial limit testing for product release and stability evaluation. Proposals exist stating that products with a water activity of
0.6 or less would not require routine testing for objectionable organisms.
Rotronic – Water activity measurement
3
PRODUCT OVERVIEW
Rotronic offers a complete range of products for measurement of water activity. The instruments are accurate and boast high
efficiency, compatibility and simple calibration. Combine the measurement heads, insertion probes, benchtop display units and
handheld instruments as you need.
Product overview
Measurement unit
Display unit
Stationar y
Portable
Interchangeable probe
connector
Probe connector fitted
USB port/connector
Ethernet inter face
AwTherm
HygroLab C1
HP23-AW-A
HC2-AW-USB
HC2-AW-USB-SW
HC2-AW
HC2-P05
HC2-HP28
4 2
HC2-HP50
AwQuick function
Includes PC software
HW4-P-Quick
Dew and frost point
calculation
HW4 compatibility
Temperature controlled
4
Rotronic – Water activity measurement
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