PURPOSE: To rapidly measure the content of air with high accuracy by melting a plastic oils and fats lump containing air under heating without dissipating air and reducing pressure to a constant pressure to expand air bubbles to calculate a vol. change or calculating a vacuum degree when pressure is reduced so as to obtain a constant vol. change.

CONSTITUTION: Several grams of a sample is taken from a butter lump to be weighed and cooled to about 5°C. Alcohol of about 70°C or higher is sprayed on the sample to remove surface waterdrops and the sample is put in a U-shape pipe 4 along with cooled degassed water 5 to be hermetically sealed with grease. Next, the U-shape pipe 4 is heated to about 50°C in a thermostatic tank 7 to melt butter 5 and evacuated by a vacuum pump 1 to expel the air in the sample into water and the sample wherein butter, water and air are separated is cooled in a thermostatic tank 6 of about 20°C and the initial graduations of the U-shape pipe 4 in the horizontal state and the temp. of the thermostatic tank 6 are measured. Further, the Ushape pipe 4 is evacuated to about 150-160 Torr in the horizontal state and the graduations and pressure in this state are measured. The air content of butter can be calculated from the vols., pressure changes and wts. of a standard state and a vacuum state.