Look: Ripe yellow-fleshed peaches should have a golden hue behind their reddish blush (that blush is not a sign of ripeness! just of where the sun shone on the peach). This coloration is easiest to see that the stem end, since little sun hits the peach there and they don't tend to develop any blush. Lighter yellow color means a less-ripe peach; avoid peaches that still have a green-tinge to their color. Also check peaches for bruises, scratches, or flat areas - you want none of those! Also avoid any peaches with wrinkly skin, they were probably kept chilled after harvest for too long and became dehydrated.
Smell: Most peaches should smell like what you want them to taste like. No smell usually means no taste (yet) and an under-ripe peach. Know that some varieties can have great flavor without that knock-you-out peach smell. If you're shopping at a farmers market, ask the farmer for guidance about the variety you're inspecting.
Feel: Like any fruit, peaches should feel heavy for their size. More specifically, though, the give of a peach's flesh can tell you a lot about how ripe it is. Hold the peach in the palm of your hand and gently squeeze with your whole fingers to gauge how hard or soft the peach is:
- Baseball-hard peaches should be left behind; they were picked before being ready and most likely will never ripen properly.
- Tennis ball-like peaches are not ready to eat, but are excellent candidates for taking home for ripening to eat later in the week.
- Real "give" when you squeeze means the peach can be happily eaten or left out on the counter for a day or two first. These peaches are great for baking since they hold their shape better that softer ripe specimens.
- Soft peaches will bruise slightly when you squeeze. These are ready to eat right now.
- Super-soft peaches are already bruised, just from sitting there. They are a tad over-ripe, but can make for tasty, if exceedingly juicy and messy, eating.
If you somehow end up with a mealy peach, know that they are almost always the result of peaches being picked either very green or very ripe and then chilled, then brought to room temperature. Avoid whoever sold it to you in the future!