A Comparison of Vacuum and Steam Distillation for Determining the Volatile Acidity of Evaporated Milk

Summary 1. A method of determining formic acid and volatile acid values in heated milk by means of vacuum distillation at constant volume is presented. Results of experiments to determine the recovery of added formic acid from sterilized evaporated milk by the steam and vacuum distillation procedures are discussed. 2. The formic acid content of reconstituted evaporated milk averaged about 32 mg./l. by steam distillation and about 40 mg./l. by vacuum distillation. 3. The total volatile acid content of reconstituted evaporated milk, expressed as formic acid, averaged 134 mg./l. by steam distillation and 70 mg./l. by vacuum distillation. 4. The vacuum and steam distillation procedures both gave satisfactory recovery of added formic acid from sterilized evaporated milk by the gravimetric method. 5. There was no evidence of production of formic acid during steam distillation as far as the accuracy of the methods could detect. 6. Titrations of volatile acids on the steam distillates were considerably higher than on the vacuum distillates. The difference could be due to continuous evolution of carbon dioxide from the milk during steam distillation, the more rapid distillation rate of butyric and caproic acids with steam, and/or splitting of glycerides of fatty acids during steam distillation. 7. The addition of formic acid to the milk appeared to reduce the amount of volatile acids not formic obtained by steam distillation. 8. The vacuum distillation showed an advantage over steam distillation where a consideration of the total volatile acids in the distillate was desired.