STEM連繫 9.1STEM connection 9.1酸和鹼在食品加工上的用途Use of acids and alkalis in food processing
學習技能：Learning skill:
DIYDIY
難度﹕Difficulty:
★ ★
時間﹕Time:
數星期A few weeks
步驟Procedures
芝士
cheese
皮蛋
century eggs
用檸檬酸製造芝士Making white cheese with critic acid
1. 把大約1 L的全脂奶倒入一個煮食鍋中。
1. Pour about 1 L of whole milk into a large pot.
2. 扭開煤氣爐，把牛奶用中火慢煮。過程中不斷攪拌牛奶。
2. Turn on the gas stove and stir the milk continuously over medium heat.
3. 把大約50 mL的檸檬汁（從新鮮檸檬中提取） 加到牛奶中。
3. Add about 50 mL of lemon juice (extracted from fresh lemon) to the milk.
4. 繼續攪拌混合物，直至混合物變成凝乳狀物。
4. Stir the mixture again until the mixture separate into curds.
5. 把凝乳狀物倒進煲湯袋作過濾，然後把多餘的液體除去。
5. Pour the curds through a food filter bag and then remove any excess liquid.
6. 等待30分鐘，你已製成一塊芝士了！
6. Wait for about 30 minutes and you have made some cheese!
用氫氧化鈉製造皮蛋Making century eggs with sodium hydroxide
1. 我們需要用「食品級」（food grade） 氫氧化鈉來製造可食用的皮蛋。
1. We need to use ‘food grade’ sodium hydroxide to make edible century eggs.
2. 把大約1 L的熱水倒入一個塑膠容器中。
2. Add about 1 L of hot water into a large plastic container.
3. 把大約50 g的食鹽加入容器中，然後攪勻。
3. Add about 50 g of salt into the container and stir the mixture well.
4. 把大約50 g的氫氧化鈉加入容器中，然後攪勻。（需要戴上安全眼鏡及膠手套）
4. Add about 50 g of sodium hydroxide into the container and stir the mixture well.
5. 小心把數隻新鮮鴨蛋放進溶液中。
5. Carefully place some fresh duck eggs in the solution.
6. 把鴨蛋放在室温的環境中，靜置四星期。
6. Place the eggs at room temperature for about four weeks.
7. 四星期後，把鴨蛋放進雪櫃，靜置數小時。
7. After four weeks, put the eggs in the refrigerator for a few hours.
8. 把鴨蛋取出，再用清水沖洗鴨蛋。
8. Then, rinse the eggs with water.
9. 把鴨蛋的蛋殼剝掉。
9. Remove the egg shell of the eggs one by one.
10. 你已製成一些皮蛋了！
10. You have made some century eggs!
試想想Think about
1.
Suggest any other uses of acids and alkalis in food processing.