ISO 23291:2020

Overview

ISO 23291:2020 - “Milk and milk products - Guidelines for the application of in-line and on-line infrared spectrometry” provides guidance for applying infrared (IR) spectrometry in dairy processing for real‑time and near‑real‑time quality control. The standard is focused on in-line and on-line IR systems (distinct from ISO 21543 | IDF 201) and covers use of near infrared (NIR) and mid infrared (MIR) spectrometry to estimate constituents such as protein, fat, total solids and moisture in liquid, semi‑solid and powder dairy matrices.

Key topics and technical requirements

• Scope of measurements: Determination of protein, fat and total solids in liquid milk and milk products (MIR and NIR); protein, fat and moisture in powders, butter and semi‑solids using NIR.
• Definitions: Clear differentiation of in‑line (probe directly interfaces with the product stream) and on‑line (subsampling via bleed loop or automated sampler) analysis.
• Principle & apparatus:
  • Measurement modes: transmission, reflectance, attenuated total reflectance (ATR).
  • Instrument technologies: dispersive (grating), interferometric (FTIR) or diode‑array devices.
  • Spectral ranges as specified: NIR (approx. 400–2 500 nm / indicated cm−1 ranges) and MIR (approx. 4 000–400 cm−1).
  • Instruments should include diagnostic tests for photometric noise, wavelength accuracy and precision.
• Installation & sampling:
  • Protect instruments from cleaning regimes, vibration, dust and temperature extremes.
  • Food‑contact material compliance (e.g., Regulation (EC) No 1935/2004 or US 3A) for probes and cells.
  • Ensure representative sampling, consistent cleaning, stable interface and correct probe placement.
  • Match spectra with reference analyses - sampling in steady‑state and minimal time lag (preferably < 1 day) to reduce sampling uncertainty.
• Calibration, validation & monitoring:
  • Use representative reference sets to build calibration models.
  • Validate and monitor long‑term performance, and apply calibration adjustment procedures.
• Performance statistics: Guidance on metrics for measurement performance and ongoing verification.

Applications and users

ISO 23291:2020 is practical for:

• Dairy process engineers and plant automation teams implementing in-line or on-line process analytics.
• Quality control and laboratory specialists integrating NIR/MIR spectroscopy for fat, protein and solids monitoring.
• Instrument manufacturers, system integrators and validation experts designing hygienic probe interfaces and calibration workflows.
• Regulatory and compliance personnel assessing food‑contact material and measurement traceability.

Keywords: ISO 23291:2020, in-line infrared spectrometry, on-line infrared spectrometry, dairy processing, NIR, MIR, calibration, sampling, real-time analysis, milk and milk products.

Related standards

• Note: ISO 23291:2020 is distinct from ISO 21543 | IDF 201 (other IR applications). Also references food‑contact regulations such as Regulation (EC) No 1935/2004 and hygienic design guidance (e.g., 3A Sanitary Standards).