Transcript Making Cheese, Bread and Gingerbeer

Making Cheese, Bread
and Gingerbeer
With the help of Micro-organisms
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 microorganisms carry out.
 The process of
respiration
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.
Anaerobic respiration
 But some bacteria and fungi can carry out respiration
without oxygen.
 Respiration in the absence of oxygen is called
anaerobic respiration.
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
By-products
 But when lactic acid bacteria carry out anaerobic
respiration, all they produce is lactic acid!
Glucose  Lactic acid
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.
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
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.
Cheese
 In class, we used vinegar as our acid for separating
the curds and whey.
 But there is a better method!
 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.
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.
Cheese
 Remember, the lactic acid is a by-product of the
bacteria carrying out anaerobic respiration.
Bread
Bread
 People have been making bread since 9000BC.
 It is made by cooking a dough of flour and water.
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?
Bread
 The answer is with
yeast.
 Yeast are unicellular
fungi.
 So when you buy yeast
at the supermarket, you
are buying a living
thing!
Bread
 The yeast we use for making bread is a species
called Saccharomyces cerevisiae.
 But there are more than 1500 other species too.
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
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.
Ginger-beer
Ginger-beer
 To make ginger-beer,
again we use
Saccharomyces
cerevisiae.
 This time we give the
yeast some ordinary
sugar for food.
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
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.
 We know that anaerobic
respiration produces
carbon dioxide and
ethanol.
 And we know that
carbon dioxide is useful
for making bread and
gingerbeer.
Ethanol?
 But what’s ethanol?
 Is ethanol useful for anything?
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!
Ethanol
 Without micro-organisms and the life process of
anaerobic respiration, there would be no alcohol of
any sort.
Recap
 Some bacteria and fungi carry out anaerobic
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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.