When milk is spilled, the occurrence of bad smell is a matter of time. If the milk stays untouched for awhile, the odour of spoiled milk will be quite sensible after a day or two. To minimize the stench, you should mop up the mess as soon as you notice it. Since the smell of rotting milk is caused by bacteria, spilled milk responds better to natural cleaning products. Commercial cleaners may actually cook the milk onto the carpet, causing a permanent staining.
