AbstractEighteen commercial silages from ten different farms located in south‐east Scotland were exposed to air in polystyrene containers over a 9‐day period. The silages were subjected to detailed biochemical and microbiological analyses prior to aeration. All the parameters used to measure aerobic deterioration, pH rise, maximum temperature above ambient and sum of temperature rise showed a good correlation with dry matter loss. In a comparison of silage parameters with deterioration measurements, only ammonia nitrogen contents were correlated with all the measurements. The results of microbial counts are inconclusive. Yeast counts increased during the 9‐day aeration period whether dry matter losses were high or not.