Fruit and Vegetable Processing
Fruit and Vegetable Processing
This domain tests canning, jam/jelly, drying, juices and minimal processing. Expect standards for soluble solids, acidity and pectin.
Core rules
- Preparation: sorting, washing, trimming and blanching. Blanching inactivates polyphenol oxidase, fixes colour, removes air and shrinks tissue; over-blanching causes nutrient loss and mushiness.
- Jam, jelly, marmalade: a set needs sugar (about 65–68% TSS), acid (pH about 3.0–3.4) and pectin. Jelly uses clear fruit extract; jam uses crushed fruit; marmalade includes peel.
- Canning: acid foods are hot-filled or pasteurized; low-acid vegetables need pressure sterilization. Exhausting removes air and helps vacuum formation.
- Drying/osmotic dehydration: reduces aw; sulphite dips control browning but are regulated.
- Juices: clarification with enzymes, pasteurization and deaeration prevent browning and spoilage.
Worked example
A mango jam trial sets weakly. It measures 60% TSS by refractometer, pH 4.2 and has low natural pectin. Reasoning: 60% TSS gives insufficient osmotic preservation; pH 4.2 is too high for good pectin gel; low pectin weakens the network. Correct by adding pectin and food acid, then boiling to 68% TSS. Recheck TSS at the end because evaporation changes concentration.
Traps
Refractometer readings are temperature-corrected; do not assume all fruits need added pectin; overboiling degrades pectin and darkens colour; standards specify fruit content and TSS, so check the product category.