Q. Determine the percentage of total solids in the given samples of milk

After undertaking this activity, you will be able to:

• explain the technique of determination of the total solids in the samples of milk and milk products, and

• analyze the percentage total solids in different types of milk available.

Materials Required

Two samples of milk (toned/double toned and full cream) Shallow flat bottom dishes of aluminium alloy, nickel, stainless steel, porcelain/silica about 7-8 cm in diameter and 1.5 cm in height.

Air oven maintained at temperature 100°C

Weighing balance

Principle

The knowledge of the fat content and the specific gravity of the milk can determine total solids in milk. The percentage of total solids can be measured by the application of a simple formula as given below:

T = 0.25 G + 1.2 F + 0.14

where,

T represents the percentage of total solids

G represents the specific gravity (in degrees)

F represents the percentage of fat

The gravimetric method as discussed in sub-section 5.3.6 earlier in this practical would be used in this exercise for the determination of total solids. Write down the principle of gravimetric method here in the space provided:

Procedure

Now carry out the experiment step-by-step as enumerated herewith:

1) Weigh accurately the clean, dry empty dish with the lid.

2) Pipette into the dish about 5 ml of the prepared sample of milk and weigh quickly with the lid on the dish.

3) Place the dish uncovered on a boiling water bath.

4) Keep the base of the dish horizontal to promote uniform drying and protect it from direct contact with the metal of the water bath.

5) After at least 30 minutes remove the dish, wipe the bottom and transfer to an air oven maintained at 100°C ± 2°C.

6) At the end of one hour, remove the dish to a dessicator and allow to cool completely before weighing again.

7) To ensure the constancy of weight, the dish must be replaced in the air-oven for successive periods of 30 minutes, with intermediate weighing, until two consecutive weighing differ by less than one milligram.

8) Note the lowest weight.

9) Calculate the total solid percent by weight using the formula given herewith.