Harvested from October through March, December is the prime month for fresh chestnuts. If you are unable to find them fresh, you can take advantage of chestnuts canned, pureed, or preserved in sugar or syrup (marrons glacés).
Some specialty markets also carry frozen shelled and peeled Italian chestnuts. Canned chestnuts can be either sweetened or unsweetened and are usually imported from France, making them a bit pricey.
Choose fresh nuts that are smooth and glossy, free of blemishes. They should feel heavy for their size. Avoid any that are shriveled, cracked, or rattle in their shell. Shake the shell. If you hear movement, you know they are drying out.
Fresh chestnuts will dry out easily, so keep them in a cool, dry place, free of drafts, and use within 1 week. Fresh nuts in the shell can be placed in a perforated plastic bag and stored in the crisper drawer of the refrigerator up to 1 month, depending on the freshness factor when you purchase them. Fresh chestnuts can be frozen whole in their shells up to 4 months.
Shelled and cooked nuts should be covered, refrigerated, and used within three to four days. Cooked chestnuts, either whole, chopped, or pureed, may be frozen in an airtight container and held up to 9 months.
Dried chestnuts are a bit sweeter and less floury in texture than fresh roasted, albeit not as flavorful. The dried form is reconstituted by soaking in water before using in equal quantities as fresh ones. Soak them as you would dried beans for about an hour before cooking. Dried chestnuts are also stored like dried legumes, free of moisture and airtight. Under proper storage conditions, they can last up to 2 months or be frozen up to 6 months in a sealed container or bag.
Chestnut flour, usually only sold in fall and winter due to its short shelf life, is also available but keep in mind it is rather strong in flavor. Except for specialty dishes, it is best combined with other flours for cookies and pastries. Store chestnut flour in a sealed container in a cool, dry place and use within 1 month.