Overview
ISO 7973:1992 - "Cereals and milled cereal products - Determination of the viscosity of flour - Method using an amylograph" - specifies a standardized laboratory method to measure the viscosity of flour suspensions using an amylograph. The test records viscosity while a flour‑water suspension is heated at a controlled rate from 30 °C to the temperature at which viscosity reaches its maximum and then begins to fall (≈95 °C). The method applies to wheat and rye flour and to wheat and rye grain (after milling).
Key topics and technical requirements
- Purpose: Assess starch gelatinization behaviour and detect alpha‑amylase activity via the amylograph viscosity profile.
- Apparatus: Brabender‑type amylograph (specific characteristics required - heater coils around the bowl, torque‑measuring head changeable). Key instrument settings:
- Spindle speed: 75 ± 1 rev/min
- Temperature rise: 1.50 ± 0.03 °C/min
- Recorder linear speed: 0.50 ± 0.01 cm/min
- Sample preparation:
- Use representative laboratory samples (sampling guidance referenced to ISO 950 and ISO 2170).
- Adjust test portion mass according to actual moisture content so it corresponds to the specified dry mass (tables and a formula are provided in the standard for adjustment).
- Typical test portion: equivalents of 80 g flour (wet mass adjusted) or 90 g for milled grain procedures.
- Test procedure: Prepare a uniform flour‑water suspension, pour into the amylograph bowl, heat from 30 °C at the specified rate, record the amylogram and determine maximum amylograph viscosity in amylograph units (AU) and the temperature at peak viscosity.
- Calibration and precision:
- Annex A describes amylograph calibration procedures.
- Precision data (inter‑laboratory): repeatability and reproducibility limits are provided (e.g., absolute difference limits in the test range 197–693 AU).
Applications and users
- Practical uses:
- Quality control in flour and milling operations to monitor starch behavior and enzyme activity.
- Baking and food formulation prediction - relates to dough/starch performance during processing.
- Breeding and research - characterizing varietal differences in starch gelatinization.
- Grain trading and specification - objective viscosity data for contracts and specifications.
- Typical users: cereal and flour laboratories, millers, baking ingredient suppliers, food scientists, grain traders, and research institutions.
Related standards
- ISO 712 - Determination of moisture content (routine reference method) - used for moisture adjustment.
- ISO 3093 - Milling requirements for grain preparation.
- Sampling references: ISO 950 (grains), ISO 2170 (milled products).
Keywords: ISO 7973, amylograph method, flour viscosity, starch gelatinization, wheat flour testing, rye flour testing, amylograph units, viscosity measurement.