That's why I would not make a Kolsch with fruit, I just like Kolsch too much to put fruit in it, plus it's a beer that takes a while to really mature. I have never used apricot, but I have tried cherries and raspberry, and for my money the Oregon Fruit purees are the best. You don't have to think about sanitation and, most importantly, it will give your beer a natural fruit flavor, which I think is missing with fruit extracts. The small fruit concentrates can leave your beer tasting artificial and one dimensional, but real fruit adds complexity. I'm sure you can make a fruit good beer only using fruit concentrate but if I was putting time and effort into a brew I would the best ingredients without any shortcuts or alternatives.