Forbes magazine estimates that we throw away 113kg of food per person each year, about a quarter of the total food supply sold each year. Keeping a food waste diary can help you figure out what doesn't get eaten and why so you can adjust your shopping, cooking and eating habits to reduce this waste to a minimum.
Frugality weblog Squawkfox estimates that completely reducing your food waste can save up to $1500 each year. Few of us are going to completely eliminate that waste, but can work to reduce by using tools such as a food diary.
Anytime you end up throwing out any type of food, record it on the diary. You'll list the type of meal it came from, food item, amount, how you disposed of the item (garbage, compost, fed to pet, etc), why you threw it out, and the money wasted by throwing this out. This can get pedantic if you list every last morsel wasted (the example on the pdf lists ⅛ cup of milk leftover poured down the sink from breakfast cereal, a loss of 20c) but the idea is sound. It's basically like tracking your spending or keeping a budget so you can see where you get off track and how you can change your habits.
For other ways of reducing food waste check out our guide to how to stop wasting so much food in the kitchen.
Save money by keeping a Food Waste Diary [Squawkfox]