Prunes do grow on trees, but they are simply dried plums. The term “prune” specifically refers to the plum after it has been dried, converting the sweet, juicy fruit into a chewy, shelf-stable delicacy. This drying process concentrates the fruit’s natural sugars and nutrients.
The Plum Connection
Prunes originate from the European plum tree (Prunus domestica), which belongs to the Prunus genus alongside cherries, peaches, and almonds. Not all plums can be dried into prunes; only specific cultivars possess the necessary characteristics.
These prune-plums must have a high soluble solids content, meaning a naturally high sugar concentration when harvested. This elevated sugar level prevents the fruit from fermenting during drying. Growers favor freestone varieties, such as the ‘La Petite d’Agen,’ where the pit separates easily from the flesh. Freestone plums are more practical for commercial processing than clingstone varieties sold for fresh consumption.
From Plum to Prune: The Drying Process
The journey from a fresh plum to a finished prune involves the calculated removal of water, which intensifies the flavor and extends the fruit’s shelf life. Fresh plums are approximately 80% water by weight, and the drying process reduces this moisture content dramatically. The final product typically retains only about 25 to 30% moisture.
Commercial production uses controlled dehydration methods, often involving hot air dryers set at temperatures around 85 to 90°C for up to 18 hours. This mechanical drying ensures a rapid and hygienic process necessary for large volumes of fruit. Historically, sun-drying was employed, but this method can take over ten days and risks spoilage.
The high sugar content of the selected plum cultivar makes this dehydration possible without spoilage. As the water leaves the fruit, the concentrated sugars inhibit the growth of microorganisms, acting as a natural preservative. Roughly three pounds of fresh prune-plums are required to produce just one pound of dried prunes.
Nutritional Profile
The removal of water concentrates the plum’s nutritional components, giving prunes a unique profile valued for digestive support. Prunes are an excellent source of dietary fiber, containing both soluble and insoluble types, with about 6.1 grams per 100-gram serving. This fiber helps regulate the digestive system by adding bulk and promoting regularity.
Another functional component is sorbitol, a naturally occurring sugar alcohol that is only partially absorbed. Prunes contain a high amount of sorbitol (roughly 14.7 grams per 100 grams). This compound draws water into the large intestine, contributing to the fruit’s mild laxative effect. Prunes are also a source of Vitamin K, which supports bone health, and potassium, a mineral that aids in muscle and nerve function.