Making Cheese, Bread and Gingerbeer

1. Making Cheese, Bread and Gingerbeer With the help of Micro-organisms

2. Respiration • If we want to make cheese, bread or gingerbeer – we need micro-organisms. • To make these things, humans rely on a life process that micro-organisms carry out. • The process of respiration

3. Respiration • Respiration is the process of releasing energy from food. • Humans need to breathe in oxygen from the air for our cells to carry out respiration.

4. Anaerobic respiration • But some bacteria and fungi can carry out respiration without oxygen. • Respiration in the absence of oxygen is called anaerobic respiration.

5. By-products • One big difference between aerobic (with oxygen) and anaerobic (without oxygen) respiration is their by-products • When humans carry out aerobic respiration, we produce carbon-dioxide and water as by-products. Aerobic respiration • Glucose + Oxygen  Carbon dioxide + Water

6. By-products • But when lactic acid bacteria carry out anaerobic respiration, all they produce is lactic acid! Glucose  Lactic acid

7. By-products • And when yeast carries out anaerobic respiration it produces carbon dioxide and ethanol. Anaerobic Respiration Glucose  Carbon dioxide + Ethanol • Sometimes we call this process fermentation.

8. Cheese • There are many different types of cheese. • But they all come from milk. • It could be cows milk or goats milk. • But definitely milk

9. Cheese • When acid is added to milk, it separates into curds and whey. • The curds are the solid clumpy bits. The whey is the watery liquid.

10. Cheese • In class, we used vinegar as our acid for separating the curds and whey. • But there is a better method!

11. If you put lactic acid bacteria into milk they carry out anaerobic respiration. • They use all the lactose and glucose for energy and produce lactic acid as a by-product.

12. Cheese • This lactic acid does a great job of lowering the pH of the milk and separating the curds and whey. • It works even better than vinegar.

13. Cheese • Remember, the lactic acid is a by-product of the bacteria carrying out anaerobic respiration.

14. Bread

15. Bread • People have been making bread since 9000BC. • It is made by cooking a dough of flour and water.

16. Bread • Most of the time we want our bread to rise and to be full of little holes. • But how do we make it light? • How do we get these little holes?

17. Bread • The answer is with yeast. • Yeast are unicellular fungi. • So when you buy yeast at the supermarket, you are buying a living thing!

18. Bread • The yeast we use for making bread is a species called Saccharomyces cerevisiae. • But there are more than 1500 other species too.

19. Bread • When yeast is put with flour and water, it uses the sugars in the flour to carry out anaerobic respiration. • When yeast carries out anaerobic respiration, it produces carbon dioxide and ethanol as by-products. Glucose  Carbon dioxide + Ethanol

20. Bread • The ethanol evaporates during baking (giving a nice smell) • The carbon dioxide forms bubbles which makes the bread light, helps it to rise and gives us all the little holes.

21. Ginger-beer

22. Ginger-beer • To make ginger-beer, again we use Saccharomyces cerevisiae. • This time we give the yeast some ordinary sugar for food.

23. Ginger-beer • Remember, respiration is all about getting energy from the glucose in food. • The yeast will get energy from the sugar by carrying out anaerobic respiration. Glucose  Carbon dioxide + Ethanol

24. Ginger-beer • The carbon dioxide is useful again, because this time it forms all the bubbles that make our ginger beer fizzy. • Anaerobic respiration is very useful.

25. We know that anaerobic respiration produces carbon dioxide and ethanol. • And we know that carbon dioxide is useful for making bread and gingerbeer.

26. Ethanol? • But what’s ethanol? • Is ethanol useful for anything?

27. Ethanol • Ethanol is an organic compound with a hydoxyl functional group. • This means it’s an alcohol. And this particular alcohol is the sort we use to make our drinks alcoholic!

28. Ethanol • Without micro-organisms and the life process of anaerobic respiration, there would be no alcohol of any sort.

29. Recap • Some bacteria and fungi carry out anaerobic respiration to obtain their energy from food. • Lactic acid bacteria produce lactic acid from the lactose in milk. • This acid helps to separate the curds and the whey for making cheese. • When yeast carries out anaerobic respiration it produces carbon dioxide which is useful for making bread and gingerbeer… • And ethanol which is useful for making alcoholic drinks.