Principals of yogurt production

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• Principals of yogurt production
• Commercial yogurt production processes
• Factors affecting yogurt production
• Variation of yogurt
• Cheese production processes
• Types of cheese

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• Otherwise known as lactic cultures and are
  involved in both yogurt and cheese production
• belong to a category of microorganisms that can
  digest the milk sugar lactose and convert it into
  lactic acid        
• The starter culture for most yoghurt production
  is a symbiotic blend of Streptococcus salivarius
  subsp. thermophilus (ST) and Lactobacillus
  delbrueckii subsp. bulgaricus (LB).
• Although they can grow independently, the rate of
  acid production is much higher when used
  together.
• These microorganisms are ultimately responsible
  for the formation of typical yogurt flavour and
  texture.
• The major steps involved in a large scale
  production of lactic starter cultures are the
  following media preparation (constitution,
  mixing, straining, sterilization), inoculum
  preparation, fermentation, cell concentration by
  centrifugation, liquid nitrogen freezing, and
  packaging.

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• produced by the controlled fermentation of milk
  by adding a starter culture of yoghurt bacteria
  under controlled temperature and environmental
  conditions.
• The starter culture usually includes two or more
  different species of bacteria for more complete
  fermentation
• The bacteria digest the natural milk sugars
  (lactose) and release lactic acid as a waste
  product, causing the characteristic curd to form.
• The increased acidity causes the milk proteins to
  coagulate into a solid mass and also restricts
  the growth of food poisoning bacteria and some
  spoilage bacteria.
• A good strain of starter culture not only affects
  the flavour and aroma, it can also speed up the
  process and thus reduces the effective equipment
  cost.

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• Commercial yoghurt production is composed of the
  following steps
• 1.pre-treatment of milk (standardization,
  fortification, lactose hydrolysis)
• 2. Homogenisation ( milk is processed so that the
  cream will not separate and rise to the top).
• 3. Heat treatment
• 4. Cooling to incubation temperature
• 6. Fermentation
• 7. Cooling
• 8. Post-fermentation treatment (flavouring, fruit
  addition, pasteurisation)
• 9. refrigeration/freezing, and packaging.

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• Temperature
• The secret to tasty yoghurt is in the proper
  control of the temperature at various stages
• If the temperature is too low, the culture grows
  too slowly to adequately acidify milk and to
  achieve a good texture.
• The culture is killed if the temperature is too
  high.
• In addition, there is a subtle difference in the
  taste because the formation and secretion of
  metabolites which contribute to the overall taste
  are dependent on the growth rate.
• When the desired acidity is reached, yoghurt is
  quickly cooled to halt further fermentation and
  metabolic activity. This cooling step is quite
  critical in industrial yoghurt production it
  must be done quickly to control tightly the
  acidity of the yoghurt, which has a profound
  effect on the taste.

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• There are mainly two types of yogurt
• Stirred yoghurt is fermented in bulk, stirred and
  then dispensed into pots or sold into customers
  containers.
• Set yoghurt is made by pouring the inoculated
  milk into pots and fermenting it in the pot.

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• For most cheeses produced worldwide, heat-treated
  or pasteurized cow's milk is used
• Specifically the milk component involved in
  cheese production is a soluble protein called
  casein.
• The enzyme rennet can be used to catalyze the
  conversion of casein in milk to para-casein by
  removing glycopeptide from the soluble casein.
• Para-casein further coagulates in the presence of
  calcium ions to form a white, creamy substance
  called curd.
• As there are too many variations of cheese all
  around the world, there is no specific method to
  produce cheese but they revolve around the steps
  listed in the following slides.

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• Before the actual cheese making begins, the milk
  usually undergoes pre-treatment designed to
  create optimum conditions for production.
• Milk intended for types of cheese which require
  more than one month for ripening need not
  necessarily be pasteurised, but usually is.
•  Milk intended for unripened cheese (fresh
  cheese) must be pasteurised. This implies that
  cheese milk for types needing a ripening period
  of at least one month need not be pasteurised in
  most countries.
• Milk intended for original Emmenthal, Parmesan
  and Grana, some extra hard types of cheese, must
  not be heated to more than 40C, to avoid
  affecting flavour, aroma and whey expulsion. Milk
  intended for these types of cheese normally comes
  from selected dairy farms with frequent
  veterinary inspection of the herds.

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• Two principal types of culture are used in cheese
  making
• mesophilic cultures with a temperature optimum
  between 20 and 40C
• thermophilic cultures which develop at up to
  45C
• As said, there are many methods of producing
  cheese so there is more than one type of starter
  culture.
• Mixed strain cultures, in which two or more
  strains of both mesophilic and thermophilic
  bacteria exist to their mutual benefit, not only
  produce lactic acid but also aroma components and
  CO 2 . Carbon dioxide is essential to creating
  the cavities in round-eyed and granular types of
  cheese.

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• Single-strain cultures are mainly used where the
  objective is to develop acid and contribute to
  protein degradation, e.g. in Cheddar and related
  types of cheese
• However, all these methods are based on 3 main
  principals
• ability to produce lactic acid ( main task of
  the culture )
• ability to break down the protein and, when
  applicable,
• ability to produce carbon dioxide (CO 2 )

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1. Curd Formation- process of introduction of a
coagulating agent (acid and/or a coagulating
enzyme), adjusting the temperature, and adding
salts. Most varieties of cheese are produced by
enzyme coagulation or rennet. Rennet coagulates
milk by precipitating casein. After the curd is
formed, the enzyme is either inactivated or
expelled together with the whey. Acid coagulation
of milk involves the addition of a culture of
lactic acid-producing bacteria (starter culture)
to warm milk. The specific starter culture
depends on the type of cheese being produced.
Cheese made by acid coagulation tends to be
unripened. The temperature for coagulation of
milk is carefully controlled and varies with the
type of cheese being made. The combination of the
temperature of coagulation, the starter culture,
the coagulating enzyme, and the acid produced
influences the rate of formation, the firmness,
the elasticity, and other physical properties of
the resulting curd and the degree of whey
expulsion.
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• 2. Cutting or Breaking Curd
• 3. Cooking Curds
• 4. Draining or Dipping Curds
• 5. Knitting of the Curds
• 6. Salting of Curds
• 7. Pressing Curds
• 8. Ripening or Curing

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• Granular texture cheese
• Round-eyed cheese
• Closed texture cheese

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• http//www.dairyconsultant.co.uk/pages/yoghurt.htm
  
• http//www.itdg.org/docs/technical_information_ser
  vice/yoghurt.pdf
• http//www.engr.umd.edu/nsw/ench485/lab8.htm
• http//www.foodsci.uoguelph.ca/dairyedu/yogurt.htm
  l
• http//www.glue.umd.edu/nsw/ench485/lab1.htm
• http//www.food-info.net/uk/dairy/cheese-productio
  n.htm
• http//www.nationaldairycouncil.org/NationalDairyC
  ouncil/Nutrition/Products/cheesePage3.htm

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Ho Kok Ching Hsien ( 5 ) Koh Keith ( 26
) Camelia Kho Zhi Hua ( 8 ) Ng Wei Jie ( 31 )