To compare processing methods, calculate what each one keeps, then weigh that against another property such as shelf life. Write a claim, the numbers behind it, and one limit.
This lesson is part of nutrition and food technology. It builds on explaining preservation principles.
How do I compare methods on an equal basis?
Turn each result into a percentage of the raw value. Percentage retained = processed value ÷ raw value × 100.
This matters because the raw food is the fair starting point. A method that leaves 30 mg looks small until you know the raw food had 60 mg.
Worked example: a green vegetable
The table is original. It shows vitamin C in 100 g of the same vegetable after different treatments.
| Treatment | Vitamin C (mg per 100 g) | Shelf life |
|---|---|---|
| Raw | 60 | 3 days |
| Steamed 5 minutes | 48 | 3 days, refrigerated |
| Boiled 5 minutes | 30 | 3 days, refrigerated |
| Canned | 20 | 2 years, unopened |
Percentage retained. Steamed: 48 ÷ 60 × 100 = 80%. Boiled: 30 ÷ 60 × 100 = 50%. Canned: 20 ÷ 60 × 100 = 33.3%.
Claim. Steaming keeps more vitamin C than boiling, 80% against 50%, when the same vegetable is cooked for the same time. Vitamin C dissolves in water, so boiling loses more into the cooking water.
Trade-off. Canning keeps the least vitamin C, but it gives the longest shelf life, so it suits a shop with no refrigerator.
The mistake that costs marks
The common slip is to name one method as simply the best. That ignores the shelf-life column, so the trade-off is missed.
| Step | Wrong | Right |
|---|---|---|
| Calculate | Compare 48, 30, 20 only | Convert to percentage retained |
| Claim | Canning is bad | Canning keeps 33.3%, steaming 80% |
| Trade-off | (missing) | Canning lasts 2 years, steaming 3 days |
| Verdict | One best for all | Best depends on the situation |
Also keep the comparison fair. If the boiled sample were cooked for 15 minutes and the steamed one for 5, the data would not isolate the method.
A claim routine you can reuse
Write three short parts. Start with the claim, add the evidence with numbers, and end with one limit or assumption.
For example: “Steaming retains more vitamin C than boiling (80% against 50%). This suggests boiling dissolves more vitamin C. The data covers one vegetable, so it may not hold for other foods.” The claim and evidence revision desk gives you extra sentences to practise.
Check yourself
A village shop has no refrigerator. The table below compares two kinds of milk. Which suits the shop, and why?
| Milk | Storage | Shelf life |
|---|---|---|
| Pasteurised | Refrigerated | 7 days |
| UHT, unopened | Room temperature | 90 days |
Answer
UHT milk suits the shop. The table shows it stays usable for 90 days at room temperature, while pasteurised milk needs refrigeration and lasts 7 days.
Limit: the table covers unopened packs only. It does not say how long an opened pack lasts.
What to study next
Continue with discussing food production and resource use, which applies the same claim and trade-off routine to farms. Then try the nutrition and food technology practice set.
If you want a teacher to check your claims with you, see online one-to-one Science tuition.