SOP: Crismer Test for Oils
GIFSQ — Global Institute for Food Safety & Quality
Principle
The Crismer test determines the miscibility of the oil sample with a standard amyl-ethyl alcohol reagent: the temperature at which definite cloudiness appears on cooling (the turbidity temperature) is characteristic, within certain limits, for each kind of oil. The observed value is corrected for the free fatty acid content of the oil.
Apparatus required
- Test tube (1.3 × 12.7 cm), etched to indicate 2 and 4 ml capacities
- Thermometer, 0–60°C, marked to 0.5°C
- Cork with a centre hole and a side notch for a small stirrer
- Small stirrer
- Water bath
- Chilled water (15°C)
Reagents
a. Amyl-ethyl alcohol reagent: mix equal volumes of ethyl alcohol and amyl alcohol; determine the temperature at which turbidity appears when tested with almond oil as described below; adjust the alcohol mixture with water, after correction for acidity, until it becomes turbid at 70°C; use this mixture for further tests.
b. Anhydrous sodium sulphate — for drying the oil.
Procedure — Standardising the alcohol reagent
Mix equal volumes of ethyl and amyl alcohols
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Determine the temperature at which turbidity appears when tested with almond oil as described in the procedure below; adjust the alcohol mixture with water, after correction for acidity, until it becomes turbid at 70°C
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Use this standardised mixture for further tests
Procedure
Dry the oil or melted fat to be tested using anhydrous sodium sulphate; filter and heat on a water bath
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To the test tube etched at 2 and 4 ml, transfer the hot sample to the 2 ml mark; add amyl-ethyl alcohol reagent to the 4 ml mark
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Fit the test tube with the cork, passing the thermometer through the centre hole and the stirrer through the side notch; ensure that the bulb of the thermometer is covered by the liquid and suspended about equidistant from the sides and bottom
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Heat the water bath and the sample slowly, moving the stirrer up and down, until the mixture is clear; continue heating until the temperature is approximately 5°C above the point of clarification
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Raise the stirrer from the liquid without removing the cork; stop heating and allow to cool
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Observe the temperature at the first point of definite cloudiness (the turbidity temperature)
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Repeat the procedure using a new sample; duplicate readings must agree within 0.5°C
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Determine the free fatty acid content as oleic acid by the acid value method; apply the correction for acidity using the correction factors for the class of oil (drying oils: linseed, sunflower, soybean — 2.05; semi-drying: cottonseed, sesame, corn — 2.03; rapeseed — 1.61; non-drying: almond, olive, groundnut — 2.07; coconut, palm kernel — 2.01; palm — 1.72; butter fat — 1.54, each per 1% acidity)
Calculation
Crismer value = Turbidity temperature + (% acidity × correction factor)
Note: the printed equation in the source is garbled at this point; the calculation is carried here as the source describes it in words. The corrected Crismer values vary more or less within a narrow range for a given kind of pure oil. As a guide, the Crismer value of rapeseed oil should be 80–85 (Codex specifications CAC/RS 34-1970).
References
Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.
Official and Tentative Methods, 3rd edn., American Oil Chemists’ Society, Vol. 1, Cb 4-35 (1975) — correction factors reproduced with the permission of AOCS.