GEA Niro Method No. A 11 b Revised: September 2005

1.         Definition

Particle density (g/ml) is defined as the mass of particles having a total volume of 1 ml.

Occluded air (ml/100g) is defined as the difference between the volume of a given mass of particles and the volume of the same mass of air-free solids.

Interstitial air (ml/100g) is defined as the difference between the volume of a given mass of particles and the volume of the same mass of powder tapped 100 times (100x tapped powder).

2.         Scope

This method may to be used for all powders.

3.         Principle

The weighted amount of powder is added to petroleum ether in a measuring cylinder. The weight of the powder divided by the volume increase of the petroleum ether gives the particle density.

4.         Apparatus

1.    Analytical balance, capable of weighing to 0.1 mg.

2.    Calibrated 100 ml measuring cylinder with glass stopper.

3.    Rubber spatula.

4.    Pipettes – 10 ml and 50 ml

5.         Reagents

Petroleum ether.

6.         Procedure

1.    Weigh out 25 g powder into the measuring cylinder.

2.    Add 50 ml petroleum ether with a pipette and shake the measuring cylinder gently until all the powder is suspended.

3.    Using the rubber spatula, scrape down all the powder particles on the wall of the measuring cylinder. Rinse with a further 10 ml of petroleum ether from a pipette.

4.    Read the total volume of petroleum ether with suspended powder.

5.    Determine the moisture content (Method A1a), the fat content (Method A9a) and the 100x tapped powder bulk density (Method A2a).

7.         Result

8.         Reproducibility

Particle density ± 0.03 g/ml

9.         Remarks

1.    When calculating powder of different compositions, the density and the amounts of the constituents must be taken in consideration. For this purpose, the following values may be used.

 Powder material, moisture free Density at 20° C Whole milk powder (28% fat) 1.280 Non-fat milk solids 1.520 Milk fat in powder 0.940 Ca-caseinate phosphate complex 1.390 Amorphous lactose 1.520 Beta-lactose 1.590 Alpha-lactose monohydrate 1.545 Anhydrous alpha-lactose 1.545 Spray dried whey powder 1.580 Residual whey components 1.800 Demineralized whey powder 1.525

10.       Literature

·         Buma T.J.: 'The true density of spray milk powder and of certain constituents' (Netherlands Milk and Dairy Journal, 1965, 19, pp. 249-265)