Download Making yoghurt

Making Yogurt
Introduction
Eastern Europe originated yogurt. Originally goat’s milk was used. The tribe people made yogurt
under the hot sun, they put bacteria in the milk, and this turned into a pleasant tasting fermented
product. The two micro – organisms involved in the yogurt production the productions where
Streptococcus thermopiles and Lactobacillus burglarious. The commercial producer could not
afford to take any risks because the correct bacteria must be present to begin the fermentation.
To avoid any contamination the commercial producer user pasteurized milk (microbe free milk)
Factors Which Affects Yogurt Production
The concentration of starter culture: If the initial concentration is too low, other
micro-organisms might grow. If the concentration is too high this is wasteful, one of the most
effective starter culture is very important. The numbers of yogurt- producing bacteria decreases
from 109 – 106 bacteria.
Temperature at the beginning of the fermentation: The enzymes that are controlling the
metabolism of the bacteria will work at there best at a particular temperature. Streptococcus
thermopile tells you that bacterium is a thermopile. The optimum temperature for yogurt
production is 46 C.
Concentration of food: Depending on the milk you use, the food provided and possible
competition from other bacteria will be different. The nomadic tribes realized that if the milk
were heated before they put it into animal skins, the product would have turned out more
sufficient, sterilized or UHT milk is theoretically best as there are no bacteria to complete with
the yogurt forms. On the negative side, heat treatment of milk will reduce the vitamin content.
Oxygen Concentration: Oxygen is not required by the bacteria producing yogurt
Duration of fermentation: Specific chemicals are required to give the yogurt its flavour. Too
short fermentation, and these will not be produced; too long a fermentation and the product
become more acidic. Other micro – Organisms may invade and produce off flavors.
Manipulating Variables
* PH
*Temperature
* Concentration of starter culture
Concentration of starter culture
Commercially, starter cultures of 1-2 % of the milk are used. Concentrations of, say, 1-5 %
would be best used in laboratory.
Controlling Variables
* Starter concentration: An initial concentration of 1% is suitable
* Type of milk
* Oxygen concentration: No aeration should be carried out.
* PH: Milk ph is 6.7 to 6.9, but lower PHS will encourage the growth of lactobacilli
These are the variables that need to be controlled so this is classed as a fair test
Time: Commercial fermentation is about is about 3-5 hours. In the laboratory this could be
carried out overnight or over one day
Monitoring the fermentation
Qualitative and Quantitative qualities
* Qualitative – tasting it
* Quantitative – pH measurement – final yogurt pH is 4.6
* Quantitative- bacterial growth can be demonstrated using a redox indicator such as resazurin or
methylene blue
Safety Points
* Sterilized equipment to avoid contamination
* Wash hands before and after experiment
* Minimize contact with micro-organisms used
Materials And Method
First of all I measured out precisely a well-known volume of milk then I used a graduated
pipette. Then I transferred milk to the 100-cm3 beaker. I then measured accurately a known
volume of live yogurt. I then transferred yogurt to the milk. After that I inserted a ph probe into a
log it data logger. I placed the ph probe into the milk, and then I placed the beaker into a
250-cm3 beaker so that the probe didn’t cause me any difficulties. I then got my data logger to
record readings at appropriate intervals and start logging. After that I placed the beaker into a
incubator at the desired temperature.
Results 1
Time
(Hours)
0
20 Degrees
30 Degrees
40 Degrees
50 Degrees
60 Degrees
6.9
6.9
6.8
6.9
6.8
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8
9
10
11
12
16
20
24
6.9
6.8
6.8
6.7
6.8
6.8
6.6
6.8
6.7
6.6
6.6
6.7
6.5
6.5
6.4
6.4
6.3
6.1
6.1
5.9
5.7
5.5
5.4
6.8
6.7
6.6
6.5
6.6
6.5
6.6
6.5
6.3
6.2
6.3
6.0
6.1
5.9
5.8
5.6
5.4
5.3
5.0
4.8
4.7
4.6
4.6
6.9
6.8
6.6
6.7
6.5
6.4
6.1
6.0
5.8
5.7
5.5
5.1
4.8
4.7
4.6
4.6
4.5
4.5
4.4
4.3
4.3
4.3
4.2
6.9
6.7
6.7
6.6
6.5
6.5
6.4
6.3
6.2
6.0
5.8
5.5
5.2
5.1
4.8
4.7
4.6
4.4
4.5
4.4
4.2
4.3
4.3
6.7
6.6
6.4
6.3
6.2
6.3
6.2
6.1
6.2
6.1
6.1
6.0
6.2
6.1
6.0
6.1
6.0
6.1
6.0
6.0
5.9
5.9
5.8
60
Series6
50
Series5
40
Series4
30
Series3
20
Series2
10
Series1
22
19
16
13
10
7
4
1
0
Method 2
I began by measuring out accurately the milk by using a pipette. Then I transferred the milk into
a beaker, and then I measured out exactly a known volume of live yogurt. After that I transferred
the yogurt to the milk, then I checked the finished product.
Conclusion
Enzymes inside bacteria catalyze yogurt process. The efficiency of an enzyme is influenced by
temperature; an enzyme has an optimum temperature where it can work to its most competent.
The higher the temperature the more efficient the enzyme is. This is because the enzyme and
substance are combining more often. above a certain temperature the could drop significantly.
This is because the active site of the enzyme is being destroyed so the substrate is no longer fits
in. the enzyme has become denatured
Further Analysis
* Yogurt is deemed complete when set at 4.6
* The efficiency of the enzymes involved can be measured by how quickly the yogurt reaches
4.6 degrees C
* The optimum temperature was 4 degrees
* From my data I found out the optimum temperature was between 40 degrees and 50 degrees
this is because the data is fairly similar
* I could have correctly established the optimum temperature by carrying out more experiments
between 40 degrees and 50 degrees for my second experiment I will use the optimum
temperature of 45 degrees
Results 2
The optimum condition was 45degrees, the ph started at 6.9 degrees and ended on 4.6 degrees
Evaluation
Design error:
* When I placed the water bathes to the incubator, the contents properly didn’t reach the desired
temperature immediately.
*Bacterial growth could have been detected if I was using resazurin or blue methylene.
Human error:
* Masses and volumes could have been mis calculated
* There could have been errors in cell counting
* Errors may have been made whilst making buffer solutions
* Yogurt and milk are difficult to measure and is also viscous
Equipment error:
*The measurement I received from the thermometers properly wasn’t absolutely accurate
*ph meter could have been defective
Vocational Aspects
Yogurt production demonstrates fermentation by Streptococcus thermophilum
and Lactobacillus bulgaricus. Heated milk is inoculated and maintained at a given
temperature causing bacteria to grow and ferment lactose, the sugar in milk. The
bacteria produce lactic acid, which causes the milk to coagulate and adds a sour
flavor.
Be sure to follow aseptic technique and use only food-grade containers for this
experiment. You must submit a proposal on what your experimental group(s) will
entail before beginning this laboratory work.
Kamran Masood