ISO 8967:2005

Overview

ISO 8967:2005 (IDF 134:2005) specifies a standardized laboratory method for the determination of bulk density of dried whole milk, partly skimmed and skimmed milk powders - both non-instant and instant. The method is also applicable to dried whey, dried buttermilk, dried milk-based infant foods, and powders where milk fat has been replaced by another fat or where roller-drying is used.

The document defines three density expressions used in quality control: poured bulk density, loose bulk density (after 100 tappings) and bulk density (after 625 tappings), expressed in grams per millilitre (g/ml).

Key Topics

• Principle: A test portion of powder is transferred into a 250 ml measuring cylinder and the volume is recorded after transfer and after defined tapping sequences. Bulk density is calculated as mass divided by measured volume (m/V).
• Test portions: Typically 100 g ± 0.1 g; if the powder does not fit, 50 g ± 0.1 g may be used.
• Tapping sequence: Volumes are recorded after transfer (V0), after 100 tappings (V100) and after 625 tappings (V625). Densities are reported to three decimal places.
• Apparatus: Standard laboratory balance (0.1 g), 250 ml graduated measuring cylinder (specified dimensions and mass), bulk density tapping apparatus (mechanical tapping device able to deliver up to 625 taps with an interval-counting device), funnel, spatula, beaker and brush.
• Precision: Interlaboratory studies define repeatability and reproducibility limits. Repeatability: the absolute difference between two single test results in the same lab should not exceed 0.025·ρ in more than 5% of cases. Reproducibility: difference between labs should not exceed 0.04·ρ in more than 5% of cases.

Applications

• Quality control of powdered dairy products during production and prior to packaging.
• Specification checks for powder handling, storage, and shipping (bulk density affects packing efficiency and transport costs).
• Process optimisation in spray-drying and roller-drying operations where concentration, homogenization and drying conditions influence powder volume and density.
• Comparative testing of product variants (e.g., fat replacements, instant vs non-instant powders).

Related Standards

• ISO 707 | IDF 50: guidance on sampling of milk and milk products (recommended sampling method).
• ISO 787-11: refers to tamped volume apparatus and provides compatible tapping apparatus details.
• ISO 5725 (withdrawn): interlaboratory test precision methods referenced for repeatability and reproducibility assessment.

This standard supports reproducible measurement of poured, loose and tapped bulk density for dairy powders, providing actionable data for production control, specification compliance and efficient packing strategies.