Effect of Filtering Ozone-Polluted Dryer Air Through Activated Charcoal on the Flavor of Foam Spray-Dried Whole Milk

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Abstract
To determine whether the flavor of dried milk manufactured with ozone-polluted air could be improved by filtering the air through activated charcoal, a series of foam spray-dried whole milks were manu- factured using, alternately in each experi- ment, standard cellulose dust filters and activated charcoal filters in the dryer air inlet. Using cellulose filters, ozone levels of air entering the dryer were 4-17 parts per billion (average 8 ppb) and powder flavor 0.6-4.0 flavor points (average 2.0 points on a 10-point scale) lower than their parent concentrates. Using charcoal filters, ozone levels of air entering the dryer were zero, and powder flavor varied from 0.2 point higher to 0.7 point lower (average 0.1 point lower) than concentrates. Ozone levels as low as 6 parts per bil- lion, if added to charcoal-purified air, had a definitely damaging effect on the pow- der's flavor. Powder manufactured in ozone-free air, and cooled before exposure, retained its high flavor quality during moderate subsequent exposure to polluted air. The flavor quality of milk powders manufac- tured in our Dairy Products Laboratory has varied seasonally for years (3). Powders made during cold weather have been consistently good, while those made during the hot-weather season have been variable in quality. ~/(ore- over, the excellent flavor quality of powders made during a period of low background levels of ozone could be seriously damaged by adding ozone to the dryer air in concentrations re- ported by others as occurring naturally in the Washington, D.C., area during the summer. Our earlier work inferentially associated the hot-weather flavor problem with ozone in pol- luted air. Ozone decomposes to some extent on most surfaces. Activated charcoal has been used to provide ozone-free air for the study

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