Anton, welcome to the forum!
I'm afraid I have never made Valencay, nor have I had any, so I do not know the answer to your question.
However ... is this type of cheese anything like a camembert or brie? If so, it is likely that the acidity is simply allowed to go to the maximum. During the making of camembert or brie, the pH drops to 4.5-4.6 or so, about as low as it will go under the action of the lactic bacteria. But then while aging the pH rises back up, I think above 6, due to the action of the Penicillium Candidum.
Again, I may be completely on the wrong track, since I am not familiar with Valencay, so feel free to disregard!