Making prunes from plums is straightforward: you halve or slice ripe plums and dry them slowly at low heat until they’re leathery and pliable. The process works in a dehydrator, a standard oven, or even outdoors in the sun. The key variable is choosing the right type of plum, because not every variety has enough sugar to dry well.
Choosing the Right Plums
Not all plums make good prunes. The varieties bred specifically for drying are called “prune plums,” and they share one critical trait: high sugar content. European plum varieties like Italian, Stanley, Brooks, and Imperial Epineause are classic choices. These cultivars belong to the species Prunus domestica, and they can be dried whole without fermenting or spoiling during the process. The reason is sugar concentration. Fresh prune plums need a soluble solids content of at least 16 to 19 percent (depending on the cultivar) to dry successfully. That natural sweetness acts as a preservative and gives the finished prune its dense, candy-like texture.
You can dry other plum varieties, but the results will be tangier, less sweet, and more prone to spoilage during a long drying session. If you’re buying from a farmers market, ask specifically for Italian prune plums or Stanley plums. They’re typically available in late summer through early fall. Choose fruit that’s fully ripe, with at least half the skin showing deep red or purple color, and flesh that gives slightly under pressure.
Preparing Plums for Drying
Wash your plums and cut them in half lengthwise, removing the pit. If you want faster drying, cut them into quarters or slices about a quarter-inch thick. Slices dry dramatically faster than halves, so your choice here determines whether you’re committing to a half-day project or a full day and a half.
Place the pieces skin-side down on your drying racks or baking sheets. This keeps the exposed flesh facing up and prevents juice from pooling. If you’re working with whole halves and want to speed things up, a quick steam blanch of one to two minutes softens the skin and helps moisture escape more efficiently. This step is optional for slices, which dry quickly on their own.
Using a Dehydrator
A food dehydrator is the most reliable method. Set it to 140°F (60°C) and arrange your plum pieces in a single layer with space between them for airflow. Slices will take roughly 6 to 10 hours. Halves take significantly longer: 24 to 36 hours. Check periodically and rotate trays if your dehydrator doesn’t have a fan that circulates evenly.
The wide time range reflects real-world variables like how ripe your plums are, how thick you cut them, ambient humidity, and how loaded your dehydrator is. Start checking slices around the 5-hour mark and halves around the 20-hour mark.
Using an Oven
If you don’t own a dehydrator, your oven works fine, though it takes roughly twice as long. Set it to the lowest temperature available. Many ovens bottom out at 170°F or higher, which is above the ideal 140°F, so prop the door open an inch or two with a wooden spoon to let moisture escape and keep the temperature down. If your oven has a convection setting, use it. The circulating air mimics a dehydrator and cuts drying time.
Line baking sheets with parchment paper, arrange the plum pieces skin-side down, and plan for 12 to 20 hours for slices or up to three days for halves. Flip the pieces once about halfway through. Oven drying ties up your kitchen for a long stretch, so many people start in the evening and let the plums dry overnight.
Sun Drying Outdoors
Sun drying is the oldest method and requires the right weather. You need daytime temperatures of 80 to 90°F, low humidity, and at least a light breeze. Under ideal conditions, plums will dry in four to five days. Cooler or more humid weather extends that timeline.
Spread the plum pieces on drying racks (not solid trays, since you need airflow underneath) and cover them with cheesecloth to keep insects off. Each evening, move the plums into airtight containers and store them in the refrigerator overnight to prevent spoilage. Bring them back out the next morning. This daily routine is critical: leaving fruit outside overnight exposes it to dew and rising humidity that can undo a day’s progress and invite mold.
How to Tell When They’re Done
A properly dried prune feels leathery and pliable, not brittle or crunchy. When you squeeze a piece, no moisture should bead on the surface or seep from the cut edges. The flesh should be dark and slightly tacky but not sticky or wet. If you tear a piece in half, the interior shouldn’t look moist or glossy. Overdried prunes become hard and unpleasant to eat, so err on the side of a slightly softer texture and rely on proper storage to keep them safe.
Conditioning After Drying
Even in a batch that looks uniformly done, individual pieces will have slightly different moisture levels. Conditioning evens this out and prevents mold from developing in storage. Pack your cooled prunes loosely into glass jars, filling each jar about two-thirds full. Seal the jars and shake them once a day for seven to ten days. The drier pieces absorb excess moisture from the wetter ones, creating a uniform texture throughout.
During this conditioning period, check for any condensation on the inside of the jar. If you see droplets forming on the glass, your prunes need more drying time. Put them back in the dehydrator or oven for a few more hours before trying again.
Storage and Shelf Life
Once conditioned, store your prunes in airtight containers or sealed bags. At room temperature in a cool, dark pantry, they’ll keep at top quality for about six months. After opening, move them to the refrigerator in a tightly sealed container for up to six additional months. You can also freeze them for about a month, though freezing can change the texture slightly.
What Changes When a Plum Becomes a Prune
Drying concentrates everything inside the fruit. A 100-gram serving of fresh plums has about 46 calories, while the same weight of prunes packs roughly 240 calories. Fiber jumps from about 1.4 grams to 7.1 grams per 100-gram serving, which is why prunes are so well known for their digestive effects. That laxative reputation comes from a combination of the concentrated fiber and high levels of sorbitol, a naturally occurring sugar alcohol, along with plant compounds like chlorogenic acid. In other words, prunes aren’t just dried plums in terms of flavor. They’re a nutritionally distinct food with a much higher density of fiber, sugar, and bioactive compounds per bite.