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Objective: To investigate the factors which affect the production of yoghurt

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Title: Investigating The Factors Which Affect The Production Of Yoghurt Objective: To investigate the factors which affect the production of yoghurt Background summary: Fermentations are a significant way of modifying raw fresh food. The fermented product has properties that are different from the original material. The term fermentation is used in two senses. In the narrower biochemical sense, fermentation is a form of anaerobic respiration and is a means by which organisms, or cells within organisms, obtain energy from an inorganic substrate in the absence of oxygen. In the broader sense, the term is used to describe a very wide range of process carried out by microorganisms. Fermentation of milk into yoghurt is both a very ancient and a widespread practice. In Europe, they are most familiar with yoghurt from cow's milk, or from sheep, but milk from other mammals, including goats, buffalo and camels, is also used. Probably the first yoghurt was from the Middle East. Milk being carried out under warm conditions doubtless became sour, developed agreeable flavours and could be kept longer than fresh milk, with obvious advantage to nomadic people. ...read more.


They are Lactobacillus bulgaricus and Streptococcus thermophilus. Firsly, L. bulgaricus acts on milk proteins, converting it to small peptides and amino acids. These stimulate the growth of the second species, S. thermophilus, which in turn produces formic acid. This will stimulates the growth of L. bulgaricus. L. bulgaricus is mainly responsible for the conversion of lactose to lactic acid and production of some ethanal (acetaldehyde),which, with other compound, contributes to the flavour. The culture is incubated at 40 to 45 �C for 3 to 6 hours (or at 32 �C for 12 hours), then cooled rapidly to prevent further bacterial fermentation. At the end of the fermentation, the lactic acid concentration should be about 1.4 per cent with pH around 4.4 to 4.6. The pH is weakly acidic because lactic acid is an organic acid and weaker than the mineral acids. The thickening of the yogurt is the result of the coagulation of proteins. In this experiment, it is found that even though the pH decreases over time, the mixture only reach the pH 5. ...read more.


Starch or sugar may be added to give flavour or consistency. Sometimes, the milk is heated to allow evaporation and make a thicker yoghurt, though on a large scale the viscosity of the end-product is controlled by the initial mixture of milk and milk solids. The fat content can be adjusted by removing fat or by adding cream. The milk is homogenised to disperse the fat as small globules, then heated at 88 to 95 �C for between 15 and 30 minutes to pasteurise the milk. The high temperature and time used are necessary to kill bacteria which may be active at high temperature (thermophilic bacteria). Besides, milk inevitably carries a microflora from the udder, and these contaminants could act as competitors in the yoghurt-making process. The yoghurt is actually the protein casein in the milk that coagulates and form a soft gel. Conclusion: The pH of the sample mixture decreases over time until between pH 4.4 to 4.6. The lactic acid formed coagulates the milk proteins into yoghurt which is the soft gel formed. Reference: 1. John Adds, Erica Larkcom, Ruth Miller. 2003. Nelson Advanced Science: Respiration and Coordination (revised edition). Cheltenham: Nelson Thornes Ltd. ...read more.

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