Green peppercorns are the unripe berry of the piper nigrum vine, from which both black and white pepper are produced. Green peppercorns are most commonly sold pickled in brine or vinegar, or freeze-dried. But fresh green peppercorns are sometimes called for in Thai cooking, and are said to complement game and duck dishes, terrines and creamy sauces very well.
A couple of recipes we have seen call for "slathering" a piece of meat in a green peppercorn butter, or making a cucumber and yogurt salad spiked with peppercorns. They have a flavor that is described as piquant and fresh, and the aroma, bright.
Peppercorns are not often available fresh because they tend to darken with age and grow moldy. At this point, however, all your options are still open - use your peppercorns fresh, pickle your peppers like Peter Piper, or dry them in the hot sun, a dehydrator, or a very low-temperature oven (drying them in the sun is essentially what turns unripe peppercorns into grindable black peppercorns).
You can freeze almost anything, but a bag of frozen peppercorns is - in our experience - likely to work its way back to the darkest recesses of the freezer and remain there until the start of the next millennium.