Q. The shelling and consumption of barely steamed peas tossed with a little butter is a seasonal highpoint for our family. The peas we buy vary, however, in quality. Aside from opening a pod and eating its contents, what should a consumer look for when purchasing peas in the pod? Are some varieties tastier than others? If so, can one tell them apart? Why are some peas starchy and others sweet and tender? Does size matter? How are the peas one buys fresh different from those canned or frozen?

A. Whatever the pea variety, one should stick to firm pods. Those that are soft and wilted are old. The peas inside turn starchy as the sugars are enzymatically converted to starch. This conversion in the raw results in cooked peas of bland flavor and pasty texture.

The sugar-to-starch conversion is part of the normal maturing process of any seed. Corn also undergoes the same reaction if it sits in the supermarket or if left an additional day or two on the plant.

Besides firmness, an unblemished pod surface is also a quality indicator. Blemishes, which range from dried patches to brown scales, develop if the pods have been exposed to intense sunlight and/or hot, dry weather. The peas, again, undergo the sugar-to-starch conversion.

Pea variety is also related to eating quality. A hundred years ago, most pea varieties had "smooth-skinned" character. When dried, their skin did not wrinkle because they had a very high starch content. This made them perfect for drying: they lost less weight, produced more per acre, and made inexpensive soups and porridges for those of limited means.

During the latter part of the 18th century, French horticulturists developed peas of "wrinkled-skin" character. These could be eaten and enjoyed fresh, as their lower starch and higher sugar contents made them more tender and sweet. A pea party was at that time a popular pasttime.

British horticulurists, recognizing the commercial value of a pea that could be enjoyed raw, proceeded to further develop the French pea varieties. The wrinkled-skin results came to be known in this country as English peas or garden peas as opposed to the starchier field pea, which began its long, slow slide into disfavor.

There are many varieties of wrinkled-skin pea. Growers, breeders and processors differentiate them by skin toughness, color, sweetness, starchiness and pod-shattering ability (that is, how easily the pod is opened).

Fresh pea varieties are rarely the same as those used for canning and freezing. Produce handlers have found that the consumer expects a large pod and hence a large pea; the average customer chooses by pod appearance and hopes that the peas inside will be tender. And, there are many varieties of large, yet tender and sweet peas. Within a single variety, however, large size does indicate starchiness and blandness.

Canned-pea processors, on the other hand, choose varieties producing smaller peas. The pods are never seen and the consumer believes that small pea size indicates tenderness. The fanciest canned peas, the so-called French varieties or petits pois, are small and usually tender and sweet. Also, canned pea processors choose the paler varieties: since the heat required for safe canning converts bright-green chlorophyll to an olive-drab derivation, selection of dark-green varieties would be a very ugly mistake.

Frozen-pea processors choose peas for brightness of hue. The frozen-pea customer associates it (wrongly) with freshness, tenderness and sweetness. Frozen peas are also selected for tough skin. The tenderer varieties cannot survive the blanching process; it leaches out sugars (flavor) and causes the smaller peas to split open. The resulting loss in yield and quality would translate to higher prices and poor competitiveness with other frozen pea brands and with canned peas.