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The Oxygen Content of the Atmosphere in Containers of Dried Milk Packed in Nitrogen

Division of Dairy Research Laboratories, Bureau of Dairy Industry, Agricultural Research Administration, U. S. Department of Agriculture

ABSTRACT

The results confirm those previously obtained by direct measurement of the amounts and composition of the container gases, with respect to the relative importance of time, temperature, and degree of evacuation in reducing the oxygen concentration of the container gases. That the amounts of adsorbed gases do not decrease to a great extent with increases in the value of these factors within practical limits is also indicated by the desorption values obtained. If equilibrium had been attained in each case, the rate of decrease of the final oxygen content in the containers should have been of a logarithmic nature, since the percentage oxygen removed in each evacuation is a constant. However, the rate obtained practically is not of a logarithmic nature, due presumably to the fact that the values for the per cent oxygen in the container atmospheres are not equilibrium values.

The relatively high efficiency of a second evacuation stage in decreasing the per cent oxygen content of the container gases is indicated. However, the rate of desorption seems to vary with different dried milks; hence, the efficiency of gasing procedures should be established for the product concerned in each case.

In our experience the use of two stages of evacuation at 3 mm. pressure with a 3- to 4-day intervening holding period will produce a final oxygen concentration in the container of approximately 1 per cent. Increasing the duration of the holding period will reduce further the final oxygen concentration.