ANNEX IV

Method for measuring the oil content in olive cake and residues

1. MATERIALS

1.1. Apparatus

— suitable extraction apparatus fitted with a 200 to 250 ml round-bottomed flask,

— electrically heated bath (e.g. sand bath, water bath) or hotplate,

— analytical balance,

— oven regulated to a maximum of 80 °C,

— electrically heated oven fitted with a thermostatic device regulated to 103 ± 2 °C and one that can be swept with a stream of air or operated at reduced pressure,

— mechanical mill, easy to clean, and one that allows the olive residues to be ground without a rise in their temperature or any appreciable alteration in their content of moisture, volatile matter or substances extractable with hexane,

— extraction thimble and cotton wool or filter paper from which substances extractable with hexane have already been removed,

— desiccator,

— sieve with 1 mm diameter apertures,

— small particles of previously dried pumice stone.

1.2. Reagent

Normal hexane, technical grade, which must leave a residue of less than 0,002 g per 100 ml, on complete evaporation.

2. PROCEDURE

2.1. Preparation of the test sample

If necessary, use the mechanical mill, which has previously been properly cleaned, to grind the laboratory sample in order to reduce it to particles that can pass completely through the sieve.

Use about one twentieth of the sample to complete the process of cleaning the mill, discard the ground material, grind the remainder and collect, mix carefully and analyse without delay.

2.2. Test portion

As soon as the grinding operation has been completed, weigh out about 10 g of the sample to the nearest 0,01 g for testing.

2.3. Preparation of the extraction thimble

Place the test portion in the thimble and plug with cotton wool. If a filter paper is used, envelope the test portion in it.

2.4. Preliminary drying

If the olive residues are very moist (i.e. moisture and volatile matter content more than 10 %), carry out preliminary drying by placing the loaded thimble (or filter paper) in the oven heated for an appropriate time at not more than 80 °C in order to reduce the moisture and volatile matter content to less than 10 %.

2.5. Preparation of the round-bottomed flask

Weigh to the nearest 1 mg the flask containing one or two particles of pumice stone, previously dried in the stove at 103 ± 2 °C and then cooled in a desiccator for not less than one hour.

2.6. Initial extraction

Into the extraction apparatus insert the thimble (or filter paper) containing the test portion. Pour into the flask the requisite quantity of hexane. Fit the flask to the extraction apparatus and place the whole on the electrically heated bath. Adjust the rate of heating in such a way that the reflux rate is not less than three drops per second (moderate, not violent boiling). After four hours extraction, allow to cool. Remove the thimble from the extraction apparatus and place it in a stream of air in order to drive off most of the impregnating solvent.

2.7. Second extraction

Tip the contents of the thimble into the micro-grinder and grind as finely as possible. Return the ground mixture to the thimble without loss and place it back in the extraction apparatus.

Continue the extraction for a further two hours using the same round-bottomed flask containing the initial extract.

The resultant solution in the extraction flask must be clear. If not, filter it through a filter paper and wash the original flask and the filter paper several times with hexane. Collect the filtrate and the washing solvent in a second round-bottomed flask which has been dried and tared to the nearest 1 mg.

2.8. Removal of solvent and weighing of extract

Remove the greater part of the solvent by distillation on an electrically heated bath. Remove the last traces of solvent by heating the flask in the oven at 103 ± 2 °C for 20 minutes. Assist the elimination process either by blowing in air, or preferably an inert gas, at intervals or by using reduced pressure.

Leave the flask in a desiccator to cool for at least one hour and weigh to the nearest 1 mg.

Heat again for 10 minutes under the same conditions, cool in a desiccator and reweigh.

The difference between the two weightings shall not exceed 10 mg. If it does, heat again for periods of 10 minutes followed by cooling and weighing until the weight difference is 10 mg or less. Note the last weight of the flask.

Carry out duplicate determinations on the test sample.

3. EXPRESSION OF RESULTS

3.1. Method of calculation and formula

(a) The extract expressed as a percentage by mass of the product as received is equal to: where: S = is the percentage by mass of extract of the product as received, m0 = is the mass, in grams, of the test portion, m1 = is the mass, in grams, of the extract after drying. Take as the result the arithmetic mean of the duplicate determinations, providing the repeatability conditions are satisfied. Express the result to the first decimal place.

(b) The extract is expressed on a dry matter basis by using the formula: where: S = is the percentage of extract by means of the product as received (see point (a)), U = is its moisture and volatile matter content.

3.2. Repeatability

The difference between the duplicate determinations carried out simultaneously or in rapid succession by the same analyst shall not exceed 0,2 g of hexane extract per 100 g of sample.

If this condition is not satisfied, repeat the analysis on two other test portions. If, in this case too, the difference exceeds 0,2 g, take as the result the arithmetic mean of the four determinations.