Why do plums go rotten in a few days but prunes stay edible for weeks even months?

Upon harvesting, plums undergo several natural processes that contribute to their rapid deterioration:

1. Respiration: Like all living organisms, plums continue to respire after being picked. This process consumes the sugars in the fruit, producing energy and carbon dioxide. As a result, plums become softer and their flavor changes over time.

2. Ethylene production: Plums also release ethylene gas during ripening. Ethylene is a plant hormone that regulates fruit ripening and senescence. It accelerates the breakdown of cell walls and promotes softening, color change, and flavor development.

3. Microbial spoilage: Various microorganisms, such as bacteria and fungi, can easily penetrate and grow on plums due to their soft texture and high moisture content. These microorganisms cause the fruit to rot and develop unpleasant odors and flavors.

In contrast, prunes are dried plums that have undergone a dehydration process.

Drying significantly reduces the moisture content of the fruit, creating an environment less conducive to microbial growth. The removal of water also inhibits the activities of enzymes and slows down the respiration rate. As a result, prunes can be stored for extended periods without significant deterioration.

Additionally, the drying process concentrates the sugars and nutrients in prunes. This contributes to their characteristic sweet taste and increased nutritional value compared to fresh plums. The high sugar content also helps preserve prunes by inhibiting microbial growth.

Furthermore, during the drying process, prunes are often treated with preservatives such as sulfur dioxide or potassium sorbate. These chemicals further prevent spoilage and extend the shelf life of the product.

In summary, the low moisture content, concentrated sugars, and use of preservatives in prunes help inhibit microbial growth and enzymatic reactions, resulting in a shelf life that is significantly longer compared to fresh plums.