Overview
ISO 2172:1983 specifies the pycnometric method for determining the soluble solids content of fruit juice by measuring relative density at 20 °C. The method converts a measured density to sucrose concentration (expressed in g/100 g or g/100 ml) using a reference table. It is intended for clear fruit juices and clear concentrated products that contain no suspended matter. For other fruit and vegetable products, ISO 2173 (refractometric method) is recommended.
Key topics and technical requirements
- Core principle: measure the relative density of a test portion at 20 °C using a pyknometer (pyknometric method) and convert density to soluble solids (sucrose) via a standard table.
- Apparatus: 50 ml pyknometer, pyknometer funnel, water bath controllable at 20 ±0.2 °C, calibrated thermometer (0.2 °C or 0.1 °C divisions), analytical balance.
- Sample preparation:
- Thoroughly mix laboratory sample.
- Degas juices with high CO2 by shaking or filtration through cotton wool.
- Dilute concentrated juices (typically to ≈20–25% soluble solids; sometimes 8–10% is useful) in a one‑mark 100 ml volumetric flask.
- Clarify turbid samples by filtration or centrifugation.
- Remove significant ethanol (>0.5 g/100 ml) by partial evaporation and reconstitution as specified.
- Procedure highlights: rinse and dry pyknometer, determine masses for empty, water-filled and sample-filled pyknometer at 20 °C, calculate relative density, then read sucrose concentration from the table.
- Quality and reporting: perform two determinations and report the arithmetic mean (one decimal place). Repeatability requirement: difference between the two determinations must not exceed 0.1% of the mean relative density. Report method used and any non‑standard conditions.
Applications and users
- Who uses it: analytical laboratories, juice manufacturers, quality control teams, regulatory bodies and food technologists requiring an official density-based measure of soluble solids in clear fruit juices and clear concentrates.
- Practical uses: product specification and labeling, quality control of juice concentration, checking compliance with trade standards, calibration of other soluble-solids measurement techniques.
Related standards
- ISO 2173 - Fruit and vegetable products: soluble solids determination by refractometric method (recommended for turbid or other products).
- Use ISO 2172 in combination with good laboratory practice for accurate, traceable measurements of soluble solids content.
Keywords: ISO 2172:1983, pycnometric method, fruit juice, soluble solids, relative density, pyknometer, sucrose concentration, soluble solids content, ISO 2173.