Direct gas‐fired heating experiments were carried out during spray drying of milk using a ‘low‐NOx' burner in order to minimize contamination of the drying air by the combustion products in the flue gases from the burner. The burner, model CXA (Urquhart Engineering Co Ltd, England) was of the ‘excess air’ type, and was fuelled by natural gas. There was no significant difference between the mean values of the nitrate content of the skim milk powders produced by direct firing, electrical heating and the factory produced (indirect heating) sample. Only with nitrite content (NO2) was there a significant difference between the direct gas fired (0.811 ppm NO2‐) and the factory (0.460) samples, but the range of values encountered was very small (0.24–1.68). Direct gas‐fired heating using the low NOxburner did not contribute to the levels of N‐nitrosodimethylamine (NDMA) detected in the test powders when compared to the levels found in the control samples (trac