Council Decision of 14 November 1992 laying down methods for the analysis and testing of heat-treated milk for direct human consumption (92/608/EEC) (c. 608)

ANEX II U.K.

I. DETERMINATION OF TOTAL SOLIDS CONTENT U.K.

1. SCOPE AND FIELD OF APPLICATION U.K.

This procedure specifies the reference method for the determination of the total solids content of milk.

2. DEFINITION U.K.

Total solids content: The mass remaining after completion of the specified drying procedure and expressed as a percentage by mass.

3. PRINCIPLE U.K.

Evaporation of the water from a test portion at a temperature of 102 ± 2 ^oC in a drying oven.

4. APPARATUS AND GLASSWARE U.K.

Usual laboratory equipment and, in particular:

4.1.

Analytical balance

4.2.

Desiccator, provided with an efficient desiccant (for example freshly dried silica gel with a water content indicator).

4.3.

Drying oven, ventilated, thermostatically controlled at 102 ± 2 ^oC throughout the total working space.

4.4.

Flat-bottom dishes, of height 20 to 25 mm, diameter 50 to 75 mm, and of appropriate material provided with well-fitting, readily removable lids.

4.5.

Boiling water bath

4.6.

Homogenizer

5. PREPARATION OF THE TEST SAMPLE U.K.

Bring the sample of milk to a temperature of 20 to 25 ^oC. Thoroughly mix to ensure a homogeneous distribution of the fat throughout the sample. Avoid agitating so vigorously as to cause frothing of the milk or churning of the fat. If it is found difficult to disperse the cream layer, warm slowly to between 25 and 40 ^oC and with careful mixing, incorporate any cream adhering to the container. Cool the sample quickly to 20—25 ^oC.

If desired, a homogenizer may be used to assist the dispersion of the fat.

Correct results cannot be expected if the sample contains separated liquid fat or visible separate irregularly shaped white particles adhering to the walls of the container.

6. PROCEDURE U.K.

6.1. Preparation of the dish U.K.

Heat a dish (4.4.) with its lid placed next to it in the oven (4.3.), controlled at 102 ± 2 ^oC, for at least 30 minutes. Place the lid on the dish and immediately transfer to the desiccator (4.2.), allow to cool to room temperature (i.e. for at least 30 minutes) and weigh to the nearest 0,1 mg.

6.2. Test portion U.K.

Immediately weigh, to the nearest 0,1 mg, 3 to 5 g of the prepared test sample (5.) into the prepared dish (6.1.).

6.3. Determination U.K.

6.3.1. Pre-dry the dish for 30 minutes by heating it on the boiling water bath (4.5). U.K.

6.3.2. Heat the dish, with its lid alongside, in the oven (4.3), controlled at 102 ± 2 ^o C, for two hours. Place the lid on the dish and remove from the oven. U.K.

6.3.3. Allow to cool in the desiccator (4.2.) to room temperature (i.e. for at least 30 minutes) and weigh to the nearest 0,1 mg. U.K.

6.3.4. Heat the dish again, with its lid alongside, in the oven for one hour. Place the lid on the dish and remove from the oven. Allow to cool for approximately 30 minutes in the desiccator and weigh to the nearest 0,1 mg. U.K.

6.3.5. Repeat the operations described in 6.3.4. until the difference in mass between two consecutive weighings does not exceed 0,5 mg. Record the lowest mass. U.K.

7. EXPRESSION OF RESULTS U.K.

7.1. Calculation and formula U.K.

Calculate the total solids content as a parcentage by mass from:

where

W_T

=

the total solids content in g per 100 g,

m₀

=

the mass, in grams, of the dish and lid (see 6.1.),

m₁

=

the mass, in grams, of the dish, lid and test portion (see 6.2.),

m₂

=

the mass, in grams, of the dish, lid and dried test portion (see 6.3.5.).

Round the value obtained to the nearest 0,01 % (percentage by mass).

7.2. Precision U.K.

7.2.1. Repeatability (r): 0,10 g of total solids per 100 g of product. U.K.

7.2.2. Reproducibility (R): 0,20 g of total solids per 100 g of product. U.K.