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When preparing preserves, choose the best fruit—avoid pieces that are overripe, damaged, or unhealthy. Use enameled pots for cooking jam; avoid aluminum bowls, which can oxidize.
Store your winter preserves in a cool place. If you notice any mold on the surface of the jam or jelly, discard a layer about 0.5 cm thick, transfer the remaining jam to a pot, and bring it to a boil. Clean and sterilize the jar before refilling it. If the mold has spread throughout the jam or there are signs of fermentation, throw it all away; it is no longer safe to consume.
Sift the sugar before cooking the jam.
Add citric acid to help the berries retain their color, and add acetylsalicylic acid (aspirin) to help prevent spoilage.
