If you are purchasing a pre-cut watermelon that has already been sliced into halves or quarters, choose the flesh that is deepest in color and lacks any white streaking. If the watermelon is seeded, the seeds should also be deep in color, or white.
When purchasing a whole, uncut watermelon, there are several features to you'll want to evaluate. The first is its weight. A fully ripened watermelon will feel heavy for its size. Heaviness in a watermelon is a good thing because the water content of a watermelon will typically increase along with ripening, and a fully ripened watermelon will be over 90% water in terms of weight, and water is one of the heaviest components in any food
Second, look for a watermelon with a relatively smooth rind that is slightly dulled on top. The top and the bottom of a watermelon are worth determining and examining on a watermelon. The bottom or "underbelly" of a watermelon is the spot where it was resting on the ground. If that "ground spot" is white or green, the watermelon is unlikely to be fully ripe. A fully ripened watermelon will often have a ground spot that has turned creamy yellow in color. Opposite from the ground spot will be the top of the watermelon. In a fully ripened watermelon, that spot will typically not be shiny but somewhat dulled. The green color may appear in many different shades, however, from light green to deeper shades.
Perhaps most controversial about ripeness testing of a watermelon is whether or not to give it a thump. We've read many arguments both pro and con. However, among experts who recommend thumping, most seem to agree that a fully ripened watermelon will have a deeper, hollower "bass" sound rather than a solid and shallow "soprano" sound.
Finally, some grocers will be willing to core an uncut watermelon so that you can have an actual taste. (If you decide not to purchase the melon, the grocer can slice it up and sell it in sliced form.) So consider requesting this if you are uncertain as to the quality.
Uncut watermelons are best stored at temperatures of 50-60°F (10–16°C). In many regions, room temperatures will typically be warmer than 60°F and may be less than ideal for whole watermelon storage due to increased risk of decay. Better storage temperatures will typically be found in cellars or basements that are partly or completely below ground level. While we've seen one study showing increases in lycopene content when whole watermelon was stored at a temperature of 68°F (20°C), we believe that a fully-ripe or close-to-fully-ripe melon will already have outstanding lycopene content and that it would be better for you to err on the safe side in terms of decay risk if you are planning to wait several days before slicing open your watermelon.
Like temperatures above 60°F (16°C), temperatures much below 50°F (10°C) are not recommended for storage of uncut watermelons. This is due to increased risk of chilling-type injury that can decrease shelf life and flavor. (Therefore, the refrigerator would not be a good place for you to store a whole, uncut watermelon for this reason.)
With uncut, whole watermelon, one final storage precaution would be the avoidance of contact with high ethylene-producing foods like passion fruit, apples, peaches, pears, and papaya. Watermelons are ethylene-sensitive fruits that may become overly ripe too quickly under these circumstances.
Once cut, watermelons should be refrigerated in order to best preserve their freshness, taste, and juiciness. Store your cut watermelon in a sealed, hard plastic or glass container with a lid.
By Source : http://www.whfoods.com/
By Source : http://www.whfoods.com/