ISO 18787:2017

Overview - ISO 18787:2017 (Water activity in foodstuffs)

ISO 18787:2017 specifies principles and requirements for determining water activity (aw) of food products for human consumption and animal feed over the measurement range 0 to 1. The standard defines measurement principles (dew‑point, electrical conductivity of an electrolyte, or polymer permittivity), sampling and sample preparation, apparatus and calibration requirements, result expression, and precision criteria. It excludes products stored below their freezing point, water‑in‑fat emulsions, and crystalline products (e.g., sugars, salts, minerals). Annex A provides saturated salt solution values and Annex B reports interlaboratory study results.

Key topics and technical requirements

• Measurement principles
  • Dew‑point measurement: condensation on a cooled mirror to determine dew‑point and sample surface temperature.
  • Electrical/permittivity sensors: change in electrolyte conductivity or polymer permittivity to infer relative humidity (equals aw when sensor and sample temperatures match).
• Instrument and performance
  • Measurement at 25 °C ±1 °C (unless otherwise justified).
  • Internal resolution ≥ 0.0001 aw, display at least 0.001 aw.
  • Final point defined by a plateau with maximum amplitude 0.0003 aw (three consecutive readings or stability over 1 minute).
  • Linearity within calibration range; ability to remove interference from volatiles (e.g., alcohol) where needed.
• Calibration and standards
  • Use of saturated salt solutions (Annex A) or certified commercial standards; known uncertainty required.
  • Instrument check before each analytical series; adjustment if mean deviation > 0.005 aw.
• Sampling, preparation and storage
  • Sampling per sector‑specific rules; ensure representative test portions.
  • Prepare samples to uniform aw when needed; avoid procedures that alter aw (heating, freezing, crystallization).
  • After preparation, measurement should be performed within 4 hours and samples stored airtight at measurement or ambient temperature.
• Scope exclusions & special cases
  • Not applicable to frozen or crystalline products or water‑in‑fat emulsions.
  • Products containing volatiles (alcohols) may require equipment adaptations.

Applications and who uses this standard

ISO 18787:2017 is used for:

• Food safety and shelf‑life assessment - predicting microbial stability, spoilage risk, and chemical reactions.
• Quality control and product development - moisture control in snacks, dried foods, pet food, baked goods, and ingredients.
• Regulatory compliance and specification testing - contract labs, manufacturers, and auditors specifying aw measurement methods. Key users include food manufacturers, feed producers, analytical laboratories, quality assurance teams, and R&D groups focused on moisture management and product stability.

Related standards

• ISO 3696 - Water for analytical laboratory use (referenced for reagent water quality).
• Other sector‑specific sampling or moisture standards (as applicable).

Keywords: ISO 18787:2017, water activity, aw, foodstuffs, dew‑point measurement, electrical conductivity, polymer permittivity, food safety, shelf life, moisture control, animal feed.