For the past few decades the natural holes in the Swiss cheese have long been the point of debate between scientists and microbiologists. Since the first study carried out on the subject in 1917 , the researchers were practically at a loss for the explanation of the holes that marked the appearance of the Swiss Cheese. For a long time it was believed that the Carbon dioxide releasing bacteria that was found in the cheese might have actually caused the presence of the holes after all. But in a recent study all these myths were nullified because the holes were in reality caused by the inadvertent addition of hay in the milk. In olden times milk was collected in metal buckets and some traces of hay were known to have fallen in the milk. And when the cheese fermented, these particles of hay resulted in uneven holes all over the cheese.
But with the advent of technology , newer and more sophisticated collecting methods including sealed milking machines were used causing a remarkable reduction in the appearance of the holes. This is attributed to the fact that with the sealed collecting utensils it was quite impossible for the hay to get processed along with the milk, hence no or less holes.