<span>The answer is: the winter months produced less food. </span> The word "storage of food is most important" that start the passage telling that storing food in ideal condition is important. The word "a valuable source of protein in the long winter season" signifies the need to keep the food in a long time. The reason why you need to store food for the winter season is that the land produces less food than demand, so you need to supply it from storage
It is only active at a pH of around 2 because that is around the same pH as the gastric juices in the stomach which is where pepsin is used to break down proteins.