Why are the first batches of French-fries, produced in fresh oil, always too light colored and not crispy enough?

This can be answered with the physical properties of the deep-frying oil. Oil and water are unmixable by nature. During the deep-frying the food loses moisture in form of steam. This steam builds a barrier around the food so that the impact of the hot oil to the food is limited. The surface tension of the oil has a peak when it is very fresh. Therefore, the unmixability of oil and water makes the steam barrier very effective. This leads to lack of coloration and crispiness with the first batches. After a while of heating the physical changes decrease the surface tension of the oil and degradation products that act like emulsifiers increase the mixability of oil with water. That leads to lower effectiveness of the steam barrier and a higher impact of the hot oil to the food. By the way: deep-frying oils that contain the Maxfry® ingredients deliver perfect performance from the first to the last batch as the described effects are worked around by a general improvement of the heat mass transfer.