Hi, since we started getting our vegetable box delivered each week I began saving the ends of vegetables (leeks, carrots, onion skins, broccoli ends et cetera) and putting them into a freezer bag. When the bag is full I simmer and then reduce the whole lot as a stock and put it in a tupperware container. The problem is that the stock invariably ends up quite bitter. I'm not placing potatos, stalks or garlic into the stock so what am I doing wrong? Does anybody else make stock from vegetable peelings like this and have you got any tips to share? Many thanks, Will