The bacteria used to make yogurt cultures. Fermentation of lactose by those bacteria produces lactic acid, which acts on milk protein to give yogurt its texture and characteristic tang. Worldwide, cow’s milk is most commonly used to make yogurt but milk from water buffalo, goats, sheep, camels and yaks is also in various parts of the world.
Dairy yoghurt is produced using culture of Lactobacellus delbruechii subspobulgaricus and streptococcus salvanous substhermophilus bacteria. In addition, lactobacillus acidophilus and bifidobacteria are also sometimes added during of after culturing yoghurt. The milk is first heated to about 800C ( 176 degrees celcius) to kill any undesirable bacteria and to denature the milk proteins so that they set together rather than from curds. The milk is cooled to about 45 degrees ( 112 degrees F). The bacteria culture is added for 4 to 7 hours to allows fermentation.
Fermentation of milk usually occurs when milk is at above 45 degrees celcius. Streptococcus thermophiles start to grow first which drops milk pH from 6.6 to 5.0 and produces carbon dioxide and lactic acid. The products stimulate lactobacillus bulgarius to grow and further drop the pH to 4.2. the sugar from the milk breaks down to glucose subunits when the starter culture is added. After the formation of glucose , the sugar is then fermented into lactic acid and by the microorganism , acetylide is also produced, this chemical creates the taste and sourness of plain yourgut. The compound causes the decrease in the pH of the milk used and causes the casein, protein found in milk , molecules to produce yoghurt.
The card used in yogurt making can be prepared by adding to milk things like lemon or vinegar to fresh milk. The consistence depends on the milk. The bacteria used in the production of yoghurt all produce lactic acid during the fermentation of lactose. The lactic acid lowers the pH, and makes it tart, causes yoghurt to thicken. The lactic acid also acts as a preservative since most bacteria cannot survive in such acidic conditions.
Thye rate of acid production is high when bacterial cultures are used in combination. Critical factors during yoghurt production include: A good sterilisation and cooking technique with propersterilisation and cooling of milk, proper cleansing and heat treatment of glassware, and keeping out unwanted bacteria. Also there is need for proper incubation temperature. Lactobacillus and streptococcus thermophiles are thermophilic bacteria, meaning they prefer elevated temperatures for growth. At such temperatures ( 50 degrees celcius) pathogenic or putrefactive bacteria are inhibited. However these bacteria are inhibited. These bacteria are however killed when exposed to temperatures more than 55 degrees celcius, and do not grow well below 37degreees celcius. It will thus be incubated at 50 degrees celcius temperature on the high size of its preferd growth temperature on the high size of its presered growth temperature( 122 degrees F) a temperature which inhibits growth of pathogenic bacteria
Also critical is the importance of the protection of the starter culture from contamination. Do not open the starter culture until ready to make next batch of yoghurt. It is preserved by its acidity which inhibits growth of pathogenic bacteria. Sometimes certain conditions can lead to starter failures. These can include the presence of bacteriophages which specifically attack the bacteria. Antibiotic residues due to antibodies given to the cows can also end up in milk. The antibiotics inhibit or kill starter cultures. Starter failures can also be caused by residual sterilisation chemicals from the cleaning of equipment.
Flavours can aslo be added to the yoghurt to produce variety.
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