Fruits
Senior 2 · Agriculture
Fruits
Lesson 5 of 5
22 min
Let's begin
In the peak of the mango or avocado season, prices at the market fall and piles of fruit rot beside the road. A few months later the same fruit is scarce and expensive. The moment a fruit is picked it starts to deteriorate, and much of what farmers grow is lost between the tree and the table.
Post-harvest handling, preservation and processing reduce that loss, spread supply through the year and turn cheap surplus fruit into juice, jam and dried snacks worth far more.
Post-harvest technology aims to: keep produce cool; reduce water loss; slow ripening and other undesirable chemical changes; avoid bruising; keep produce clean and safe (sanitation); and so extend shelf life, maintain quality and meet market standards.
| Technique | How it works | Fruit examples |
|---|---|---|
| Careful handling and cooling (shade, cold rooms, refrigerators, evaporative coolers) | Low temperature slows respiration, ripening and microbes | Avocado, passion fruit for export |
| Controlled ripening | Some fruits (avocado, mango, banana) are picked mature but hard and ripen after harvest, so they survive transport | Avocado |
| Drying (sun, solar drier) | Removing water stops microbes and enzymes | Pineapple, mango, banana slices |
| Sugar (jam, jelly, marmalade, syrup) | High sugar draws water out of microbes by osmosis | Jam from pineapple, passion fruit, strawberry |
| Heat (pasteurisation, bottling, canning) | Heating kills microbes and enzymes; sealing stops recontamination | Pasteurised juice, bottled fruit |
| Chemical preservatives | Permitted amounts of substances such as sodium benzoate stop microbe growth | Juices and squashes |
| Fermentation | Yeasts turn sugar into alcohol, which prevents other microbes | Banana beer (urwagwa), fruit wines |
| Freezing | Very low temperature stops microbes and slows enzymes | Fruit pulp |
Many products combine methods: jam is boiled (heat), has high sugar, and is sealed in a sterilised jar.
Juices and nectars (passion fruit, pineapple, mango, tree tomato), jams and jellies, dried fruit, fruit pulp and concentrate, wines and banana beer, avocado oil for food and cosmetics, and fruit-flavoured yoghurt and ice cream.
Question: Keza slices 10 kg of fresh pineapple containing 85% water. She dries it until the dried slices contain 15% water. What mass of dried pineapple does she get?
Step 1: find the solids, which do not change during drying. Solids = 100% − 85% = 15% of 10 kg = 0.15 × 10 = 1.5 kg.
Step 2: in the dried product, solids are 100% − 15% = 85% of the mass. Dried mass = 1.5 ÷ 0.85 ≈ 1.76 kg.
Interpretation: 10 kg of fresh fruit becomes less than 2 kg of dried fruit. It is much lighter to transport and keeps for months, so each kilogram must sell for more than five times the fresh price to be worth it.
Tip
Memory hook: spoilage needs "water, warmth and wounds"; every preservation method removes water, removes warmth, or protects against wounds and microbes.
Exam technique: for each preservation method, explain the principle (what it does to microbes or enzymes), not only the name.
Distinguish between fruit processing and fruit preservation.
Solution: Preservation keeps fruit safe and of good quality for longer by slowing spoilage. Processing changes raw fruit into a different product, such as juice or jam; most processing also preserves.
Give three causes of spoilage in fresh fruit.
Solution: Any three: microorganisms; the fruit's own enzymes; respiration; water loss; bruising and cuts; pests.
Explain how sugar preserves fruit in jam.
Solution: The very high sugar concentration draws water out of microbial cells by osmosis, so they dehydrate and cannot grow.
Why are export avocados picked while still hard?
Solution: Avocado ripens after harvest. Hard, mature fruit survives handling and transport without bruising, then ripens at its destination.
20 kg of fresh mango (80% water) is dried to 10% water. Find the mass of dried mango.
Solution: Solids = 20% of 20 kg = 4 kg. In the dried product solids are 90%, so dried mass = 4 ÷ 0.9 ≈ 4.44 kg.
Summary
Sources and credits
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
