In general, a food is considered to have a high oxalate level if there are more than 10 milligrams of oxalates per serving of the food. High oxalate fruits include many berries, including blackberries, blueberries, raspberries and strawberries. Red or purple grapes also tend to contain a high level of oxalates. Plums, currants, kiwis and tangerines also top the list for high-oxalate foods.