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

for our water activity

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

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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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PRODUCTS

AwTher m

Temperature-stabilized measurement

The AwTherm is a professional high-end laboratory analyser for temperature-stabilized measurement of water activity in the food,

pharmaceutical, cosmetics and other industries.

The wide control range permits measurements to be integrated directly in the temperature controlled manufacturing or storage

process. Water activity measurement reacts ver y sensitively to variances in temperature. Stabilizing the temperature prevents im-

precise results due to external temperature influences. Tested at 25 °C, AwTherm therefore fulfills the requirements of ISO 21807

(Microbiolog y of food and animal feeding stuffs – Determination of water activity), which requires measurement at 25 °C.

Order code

AwT herm-PS14

AwT herm-PS40

AwT herm-SET

AwT- MHS

AwT-PS14

AwT- PS40

!

Interchangeable measurement head

A further advantage of AwTherm is the removable measurement head, which means

that the probe can be temperature calibrated or adjusted to achieve high precision.

User friendliness

In stand-alone use, the AwTher m excels with its easy handling and clarity and, together

with the Rotronic HW4 software (FDA 21 CFR part 11 compliant), should be available in

any laboratory.

Features

• Accuracy: ±0.005 aw, ±0.1 K

• Temperature control range: 0...60 °C

• High temperature stability: ±0.01 °C / min

• Measurement repeatability: 0.002 aw

• Variable sample container sizes: 14 / 40 mm

• Interchangeable reference probes for cleaning or calibration

• Aw Quick function for fast measurement results

(typically 4-5 minutes after reaching a stable temperature)

• Aw Equilibrium method available

AwT-MHS: Interchangeable measurement head

Fully automatic aw measurement can be planned if the AwTherm is connected to the HW4 soft­ware. The instrument then moves to preset temperature points automatically and carries out a
pre-selected Aw Quick or Aw Equilibrium measurement.

Rotronic – Water activity measurement

5

PRODUCTS

HygroLab C1

Laboratory application

The HygroLab C1 is a laboratory analyzer for water activity measurements with up to four interchangeable measurement heads.

The possibility to combine measurement heads and insertion probes makes the HygroLab C1 extremely flexible.

Order code

HygroLab C1

Hygr oL ab C1-SET-40

Validated software

The HygroLab C1 is easy and intuitive to use. It offers a high degree of user friendli-

ness and the possibility to connect the benchtop display unit to a PC running Rotronic

HW4 software (included in the SET) using a USB cable and via the Ethernet.

The HW4 sof tware can be used to configure instruments and as a remote control for

the complete system.

Features

• 4-channel benchtop display unit for the measurement of water activity,

relative humidity and temperature

• Aw Quick function for fast measurement results (typically 4-5 minutes)

• Aw Equilibrium method available

• Multi-channel display

• Suitable for applications throughout industr y

• Audible alarm to indicate completed aw measurement

HygroPalm23-AW-A

Mobile application

As a mobile laboratory unit, the HygroPalm HP23-AW-A is perfect for on-site water activity measurements to determine the sta-

bility and preservability of the sample being analyzed. Like the HygroLab C1, the HP23-AW-A can also be used with measurement

heads or insertion probes (two can be connected). The HygroPalm can be controlled externally using the HW4 software running

on a PC.

Order code

HP23-AW-A

HP 23 -AW-SE T-14

HP23-AW-SET-40

6

Rotronic – Water activity measurement

Portable and handy

The handheld instrument for measurement of water activity has the same functions

as the HygroLab C1, but is handier in its portable version.

Features

• 2-channel handheld instrument with multi-channel display for measurement

of water activity, relative humidity and temperature

• Aw Quick function for fast measurement results (typically 4-5 minutes)

• Aw Equilibrium method available

• Audible alarm to indicate completed measurement

• Saves up to 10,000 measured values

• Battery charging function via a USB mains adapter cable (AC1212)

Aw measurement head HC2-AW

PRODUCTS

The aw measurement head was developed for use in combination with the HygroLab C1

and the HP23-A-AW handheld analyser. This digital probe enables quick and easy

measurement of water activity. It can be calibrated via the HygroLabC1, HP23-A-AW

or via the HW4 PC software.

The sample holder size is reduced to a minimum, thereby making it possible for

humidity equilibrium to be reached quickly for all products being tested, while the

metal housing ensures high temperature stability. All critical surfaces are made of

chrome steel for minimal soiling.

You can find information on sample holders, disposable plastic sample containers

and the clamp sealing mechanism under Accessories on the Rotronic website and in

the main catalogue.

Aw measurement head HC2-AW-USB

This USB measurement head can be connected directly to a PC and comes in a set

including software or as a single instrument for addition to a system.

The set HC2-AW-USB-SW contains the HW4 software with AW Quick function,

thereby opening up all the possibilities of water activity measurement. It can be ex-

tended into a multi-station application with up to 64 measurement heads used with

a powered USB hub.

Order code

HC2-AW

Order code

HC2-AW-USB

HC2-AW-USB-SW

Features

• Measurement range: 0…1.00 aw (0…100 %RH), -40…85 °C

• Direct USB PC connection

Clamp sealing mechanism

Under certain circumstances additional mechanical sealing of the AW measurement

station and sample holder may be necessary to prevent external conditions influenc-

ing the sample. The AW-KHS ensures a strong mechanical seal and is compatible with

the WP-40 and WP-40TH sample holders.

Order code

AW-KHS

Rotronic – Water activity measurement

7

PRODUCTS

AW insertion probes HC2-P05, HC2-HP28, HC2-HP50

Direct measurement

This probe is suitable for direct measurement of water activity in bulk material sam-

ples such as powder, granulated materials, corn and grain. The HC2-HP is equipped

with a robust stainless steel probe with a diameter of 10 mm and interchangeable

sinter steel dust filter for measurement in dusty bulk materials. The HC2-P05 is the

ideal measuring instrument for dust-free applications such as tablets, gel capsules

and granulated plastics.

Features

• 5 mm insertion probe, for water activity measurement

in dust-free bulk materials (P05)

• 10 mm insertion probe for water activity measurement

in dusty bulk materials (HC2-HP28 and HC2-HP50)

Water Activit y sets

The different aw start sets contain ever ything needed

to measure water activit y and calibrate the measuring

instruments to confirm sensor performance.

HP23-AW-SET-40

Order code

HC2-HP05

HC2-HP28

HC2-HP50

HP28

Order code

HP 23 -AW-SE T-14

HP23-AW-SET-40

HygroLab C1-Set-40

AwT herm-Set

P05

HP50

Sample holders and disposable sample containers

Sample holders and disposable sample containers

The sample holders ensure optimal temperature stability for the product. The WP-40TH

sample holder can be combined with a water jacket for additional stabilization of the

temperature.

The disposable sample containers (PS-14 and PS-40) ensure optimal utilization of

the volume in the sample holder. They prevent the sample holders from coming into

direct contact with the product being tested, thereby preventing soiling or cross con-

tamination. The disposable sample containers also provide a convenient means of

collecting and storing samples.

PS-40PS -14

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Rotronic – Water activity measurement

WP -14-S WP-40 WP-40TH

Order code

PS -14

PS-40

WP -14-S

WP-40

WP-40TH

HW4 sof tware

AwQuick Mode

Batch Number: 1443
Product Name: Cereals
Comments: Cereals stored in ambient conditions

Dwell Time: 4[min]

Temperature stability: 0.04[°C/min]
Date: Dienstag, 22. November 2016
Time:09:11:04

Input Name: AW-USB

Probe S/N: 0060985604
Elapsed Time: 00:04:27
Water Activity: 0.7975Aw

Temperature: 22.43°C

______________________________________________________________________
Configured by
HW4 User name: Rico Hasler

User description: Admin

User ID number: 1453247
______________________________________________________________________
HW4 Information

Version:V3.8.0.16151

HW4 ID:01 33818116
_______________________________________
User Events File

c:\users\rico.hasler\appdata\roaming\rotronic_hw4\event\HW4USER_2016.evt
______________________________________________________________________

SOFTWARE

Full compatibility

The HW4 sof tware is compatible with all Rotronic products with USB, UART or Ether-

Order code

HW4-P-Quick

net interfaces and runs on all WINDOWS 7/8/10 operating systems.

Functions

• Live display of current measured

values

• Recording of measured values

• Configuration of instruments

• Alarm function with e-mail

• AwQuick function (HW4-P-QUICK)

• Measurement within 4-5 minutes

• User management

• Probe calibration and adjustment

• Online calculation of humidity

and aw values

Viewing of measured values / Monitoring

Viewing of measured values is very easy and user-friendly. Files of any device shown

in the device tree can be copied and opened directly with the HW4 explorer. The data

is presented in both tabular and graphical formats. The graph module can be config-

ured by the user.

PDF report available

Instrument configuration

The HW4 P C soft ware can be use d to adjust the set tings of Rotr onic instrument s and probes. Dep ending on the instru ment and probe,

the following functions and settings can be changed:

• general device settings

• password protection of device settings

• change the system units: metric / Imperial

• AwE and Aw Quick

• aw mode settings

• validation FDA 21 CFR part 11

Water activity measurement setup with HW4 PC softwareHW4 measured values shown graphically

Rotronic – Water activity measurement

9

HygroGen2 S & XL

CALIBRATION

This mobile calibration system is appreciated around the world

as it generates stable temperature and humidity conditions

quickly and saves considerable time in the calibration of all t ypes

of humidity measuring instruments from all manufacturers.

The HygroGen2 calibrates measuring instruments across their

complete working range and fulfills strict quality and confor-

mity regulations, as a result of which it has become a lead-

ing instrument in its class par ticularly in the pharmaceutical

industr y.

The chamber volume of the XL version is 10 times greater than

that of the HygroGen2-S, making it perfect for companies that

need to calibrate a large number of probes and complete mea-

suring instruments regularly.

Calibration variant ISO 17025

Arrange a calibration appointment with our SCS team and we

will reser ve our accredited equipment for your devices. Should

your devices not attain ISO 17025 calibration, we will offer you

a factory calibration certificate.

Order code

HG2-S

HG2-XL

HG2-S

HG2-XL

Order code Nominal value Measurement

uncertainty

at 23 °C

EA00-SCS 0.5 %RH

EA10-SCS 10 %RH

±0.3 %RH

EA11-SCS 11.3 % RH

International unit

National standard

Accredited agency

End customer

Consumer

Validation: Rotronic offers validation of both the HygroLab C1 and

the AwTherm. Please contact us for further details.

SI unit

METAS

SCS 0065

Consumer

EA20-SCS 20 %RH

EA35-SCS 35 %R H ±0.4 %RH

EA50-SCS 50 %RH

±0.6 %RHEA60-SCS 60 %RH

EA65-SCS 65 %RH

EA75-SCS 75.3 %RH

±0.7 %RH

EA80-SCS 80 %RH

EA95-SCS 95 %RH ±0.8 %RH

SCS-certified humidity standards

Enables end-user calibration and adjustment of Rotronic or

third-par ty probes on site. With the Rotronic humidity stan-

dards, a calibration device, service cable and the HW4 soft-

ware running on a PC, this is easy to do. The HygroLab C1 and

HP23-A can also be calibrated and adjusted without software.

10

Rotronic – Water activity measurement

Probe and sample
holder form a tight seal
together

Sample holder
typically stainless steel

product to be measured

THEORY

White paper

WATER ACTIVITY

The measurement of water activity (aw) or equilibrium relative humidity (ERH) is a key parameter in the quality con-

trol of moisture sensitive products or materials. Water activity is by definition the free or non-chemically bound water

in foods and other products.

C

ontent

Theory 2

What is water? 2

What is water acti vity? 2

What produc ts contain water 2

Why measure water activity? 3

Water activit y (aw) of some common foods 3

Water migration wi thin a product 4

What is static equilibrium? 4

How to control water ac tivity? 4

How can water act ivity measurements be

applied in the real world? 4

Total water in a product 4

What is moisture content? 4

Is it possible to correlate water ac tivity and

moisture content? 4

What should I measure: water act ivity or

Fig 1: Fresh apple and dried apple rings (different levels of water activity).

How to carr y out a test procedure 5

How to carry out a water activity measurement 6

Temperature control 7

What measurement principle is use d? 7

How can I be sure that all of my measurement s

are correc t? 7

How long is the calibration cer tificate valid? 7

Calibration and adjust ment options 7

Is there any way to accelerate the mea surement

if it takes too long? 8

What other func tions does the software of fer? 8

Products 9

For more information 10

How to carry out a water activity measurement? Temperature control?

1. As a qualitative measurement it is important that variables are eliminated when

performing measurements, this includes temperature and sample preparation.

2. Place a sample of the product to be measured into a sample cup (14 or 40 mm

deep). Recommendation: fill up to within 3 mm of the rim if possible. The less air

in the container, the faster the time to achieve equilibrium.

Important: Do not allow the sample to touch the measurement probe head!

Contamination of the measurement head will falsify all other measurements

made with other product samples.

3. Place the sample cup into the sample holder.

4. Close the lid or place the measurement head on the sample holder.

Important: the probe and sample holder must form a tight seal. Only with this

seal is the system closed and equilibrium can be achieved. Rotronic manufac-

tures a clamp sealing mechanism.

5. Water activity can be measured in two ways. Either using a predictive model or

by waiting until the water vapor pressure and the temperature have reached

equilibrium within the measurement chamber. Rotronic devices have a predic-

tive model, the AwQuick, embedded software to perform this process quickly

and repeatably.

Water activity is sensitive to tempera-

ture. Measurements can only be made

when the product sample, sample hold-

er and measurement sensors are at

stable temperatures. Many standards

require measurements to be made at a

specific temperature.

In situations where ambient tempera-

ture cannot be controlled or where you

wish to test samples at temperatures

away from ambient a temperature con-

trolled system should be used. Rotronic

provides measurement solutions for

both applications, in each case our in-

struments are designed to maintain sta-

ble temperature through the use of large

thermal mass or active thermal control.

Download the aw
Whitepaper here:
www.rotronic.com/aw

Cross section HC2-AW with WP-40

Probe with humidity and
temperature sensors

Sample cup filled with

Measurement sample not yet in equilibrium

Measurement sample in equilibrium

Rotronic – Water activity measurement

11

ROTRONIC WORLDWIDE

Rotronic is present in more than 40 countries worldwide. You can find a complete list of all our par tners on

www.rotronic.com

Rotronic International

Rotronic Par tners

SWITZERLAND

ROTRONIC AG

Grindelstrasse 6
CH-8303 Bassersdorf
Phone [phone]
Fax [phone]
www.rotronic.ch

UK

ROTRONIC Instruments UK Ltd.

Crompton Fields, Crompton Way
Crawley, West Sussex RH10 9EE
Phone [phone]
Fax [phone]
www.rotronic.co.uk

CHINA

ROTRONIC Shanghai Rep. Office

2B, Zao Fong Universe Building
No. 1800 Zhong Shan West Road
Shanghai 200233, China
Phone [phone]
Fax [phone]
www.rotronic.cn

GERMANY

ROTRONIC Messgeräte GmbH

Einsteinstrasse 17 – 23
D-76275 Ettlingen
Phone [phone]
Fax [phone]
www.rotronic.de

USA

ROTRONIC Instrument Corp.
Suite 150, 135 Engineers Road,
Hauppauge, NY 11788
Phone [phone]
Fax [phone]
www.rotronic-usa.com

JAPAN

ROTRONIC Japan KK

7th Floor, 1-13-12 Shin-Yokohama
Kohoku-ku, Yokohama
Japan 222-0033
Phone [phone]
www.rotronic.co.jp

FRANCE

ROTRONIC Sarl

56, Bld. de Courcerin
F-77183 Croissy-Beaubourg
Phone [phone]
Fax [phone]
www.rotronic.fr

CANADA

ROTRONIC Canada Inc.

236 Pritchard Rd, Unit 204
Hamilton, ON, Canada
L8W 3P7
Phone [phone]
Fax [phone]
www.rotronic.ca

ITALY

ROTRONIC Italia srl

Via Repubblica di San Marino 1
I-20157 Milano
Phone [phone]
Fax [phone]
www.rotronic.it

SINGAPORE

ROTRONIC Instrument PTE Ltd.

1003 Bukit Merah Central
#06-31 Inno Centre
Singapore 159836
Phone [phone]
Fax [phone]
www.rotronic.sg

50002E/2017-03