Ripe red plums are sweet and soft. Plums picked early in the season have tarter skins than plums picked later in the season. Plums with deep red flesh provide more antioxidant nutrition than plums with yellow flesh, according to Texas A&M University.
Plums are low in calories and contain small amounts of vitamins and minerals. One medium-sized plum delivers approximately 2 percent of the average daily requirement of vitamin A, niacin and riboflavin. An average plum delivers 1 to 5 percent of the daily calcium, magnesium, phosphorus and potassium required by adults. Plums provide trace amounts of copper, manganese and zinc.