As I mentioned in post about how to buy a Pineapple, “I’m always confused about how to pick out produce. It seems like every fruit and vegetable has its own method.” Water melon is no exception.
There are a lot of theories out there about how to pick one out. Everything from examining the strips on the melon to beating like a drum.
This last weekend we bought a nice sweet one using the following methods.
How to pick a Watermelon
1) Pick a dull looking watermelon.
I would say you could do this in a field or farmers market. In a grocery store where everything is ‘shined up’ for eye appeal this may be a bit harder.
2) Tap on it and listen.
This point is a bit debatable. The theory with this point is that amount of water in the melon will have an impact on the sound produced. A dull thud being less desirable than a sharp one. This method a very subjective and questionable method at best.
3) Pick it up and inspect it.
a) It should be uniform in shape. If it is narrow on one end or misshapen in some other way that would indicate less than ideal growing conditions.
b) It should appear to be heavy for its physical size since watermelons are about 92% water.
c) Look at the ‘field spot’ or ‘ground spot’ This is the spot on the bottom of the watermelon where it sat on the ground as it grew. The field spot should be a creamy yellowish color. The darker the color the longer it was on the vine sweetening up. If it is white or absent it wasn’t on the vine long enough and won’t be sweet.
Storing a watermelon
Uncut
Watermelon can be stored for up to 1-2 weeks, maybe even 3 if kept cool.
(researchers have found that whole watermelons kept in a cool, dark place around 55-60 degrees keep longer than refrigerated watermelons kept around 41 degrees.)
Don’t store below 40 degrees Fahrenheit otherwise the fruit will be damaged.
Keep at room temperature if you want to try and ripen it after purchase. It may look better but won’t likely get any sweeter due to being picked early.
Cut
Cut they can be stored for 3 to 4 days.
If it is cubed or sliced keep it in an air tight container.
If it is cut on one end cover that end with plastic wrap.
Covering the exposed flesh keeps it from drying out and absorbing other flavors in the refrigerator.
Cutting a watermelon
Put it in the refrigerator about 3 hours before you plan 
to eat it in order for it to cool down to the ideal eating temperature.
My preferred method is simply to
1) quarter the watermelon length wise
2) slice across each quarter to form triagulrar wedges
This video from the Chew demonstrates a quick way to cut one into cubes
Jaques Kitchen 