Very late to this discussion and none of you are probably even going to see this, but perhaps the way the quality increase works is that there's a cap of 100 quality, and the bonus from Tasting is added immediately before the quality from the cooking process? Or in other words, with rank 1 Tasting you're guaranteed to get a minimum of 15 quality on everything you cook, but if you were to cook a dish that's say, 90 quality, you'd total out at 105 which gets lowered to 100 and then the random aspect is applied. This might explain why there doesn't seem to be any effect? It's being overwritten by the other aspects of Cooking, it appears. I'm just speculating though since I haven't gone in-depth with it like some of you have!