Question 1

Does dried fruit need sulphur dioxide treatment before drying?

Accepted Answer

Sulphur dioxide (SO₂) — applied as sulphur fumigation or as a sodium metabisulphite dip — has historically been used as a pre-treatment for certain dried fruits (dried apricots, golden raisins, dried mango) to preserve the natural colour and act as an antimicrobial treatment. The SO₂ prevents the enzymatic browning (oxidation) that turns orange apricots and yellow mango brown. However, SO₂ is a declared allergen in the EU, UK, and many other jurisdictions at the levels used in dried fruit — products treated with SO₂ must carry an allergen declaration. Many buyers prefer SO₂-free dried fruit for clean-label formulations — this requires carefully selecting fruit varieties and drying conditions that minimise browning without sulphite treatment (storage in nitrogen or CO₂ atmosphere; lower drying temperatures; antioxidant alternatives). Whether to use SO₂ is a commercial and food safety decision depending on the target market and the buyer's specification.

Question 2

What is the target water activity for dried fruit?

Accepted Answer

Water activity (aW) is the measure used to predict microbial stability in dried fruit — it is more meaningful than moisture content as a safety indicator because the same moisture content gives different water activities in different products (depending on the sugar content and composition). Most dried fruits are in the intermediate moisture range: aW 0.55–0.75. At aW below 0.85, most pathogenic bacteria cannot grow; below 0.70–0.75, most spoilage bacteria are inhibited; below 0.60, most moulds are inhibited; and below 0.55, most fungi are inhibited and the product is stable. The product aW target should be set based on the intended storage conditions and shelf life: ambient storage without modified atmosphere requires a lower aW target than chilled or modified-atmosphere-packed products. Request water activity measurement equipment (a calibrated water activity meter) as part of quality control alongside the fruit drying system.

Fruit Drying Machine Manufacturers

Commercial fruit drying machines — types and selection

Fruit Drying Machine Manufacturers

Commercial fruit drying machines — types and selection

Frequently asked questions

Does dried fruit need sulphur dioxide treatment before drying?

What is the target water activity for dried fruit?

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