Hygienic milk processing procedures 1.0 Milk pasteurization

1.1 Pasteurization Pasteurization of milk is a universally known method of rendering raw milk safe through controlled heat treatment and can be defined as the process of heating every particle of milk and milk products to a pre-determined temperature and holding this temperature for a pre-determined time.

1.2 Objectives of pasteurization. Pasteurization of milk is usually done to meet at least three objectives.

To ensure that all pathogenic micro-organisms commonly found in milk are completely destroyed.

To safeguard the food value of milk; to ensure that its chemical compositions/constituents are retained as much as possible

The third objective is to ensure that other non-pathogenic bacteria and certain undesirable enzymes, which may cause spoilage, are inactivated or reduced to optimal levels.

1.3 Methods of pasteurization of Milk Basically pasteurization of milk involves three essential steps:

• Heating raw milk to a pre-determined temperature • Holding at this temperature for a predetermined time • Immediately cooling down to at least below 100 C

Therefore, the two most important variables are pasteurization temperature and the exposure or holding time. At present there are at least three accepted methods of pasteurization of milk:

1.3.1 The holding or vat method The holding or vat method, also known as the low temperature holding time (LTLT) process, is a method of holding the milk in a vat (container) to a temperature of 60- 650 C for 30 minutes. The milk is then immediately cooled to at least 100Cor less in the same container.

1.3.2 The high temperature-short time method.

This is a continuous process by which milk is rapidly brought to a temperature of 70-750C and heated continuously for 15 seconds.For all practical purposes if milk is said to be properly pasteurized it must satisfy the following three conditions:

o The milk must be cooled adequately (100C or less) before pasteurization so as to prevent the formation of heat resistant staphylococcal enterotoxin.

o The pasteurization equipment should function properly and adequately

o Precautions should be taken to prevent any post-pasteurization contamination.

1.3.3 The ultra-high temperature (UHT) method In this process the milk is heated to at least 90-1450C and held at this temperature for at least one second and then immediately cooled to at least below 100 C.

1.3.4 Sanitary problems in pasteurization plants

In order to market safe milk precautions have to be taken in such pasteurization plants:

• The plant should first of all be properly designed • The equipment used for pasteurization, storage,

packaging, cooling, etc. should be of standard design, easily washable, sterilizable etc.

• There should not be any contact or leak of unpasteurized or raw milk into the finished product

• Time keeping and thermometers are necessary at all times

• Since foam and splashed milk on the vat surface will not be properly heated, steam or hot air should be applied from the top

• All valves used in milk pasteurizing plants should be leak protector types. If any leakage occurs, the leaking milk is wasted and should not pass down the holding tube

• Manual control of milk plants has proved to be unreliable because of contamination due to carelessness.

• For this reason it is now being advocated that an automatic continuous flow type should be used.

• An automatic milk flow stop is necessary to stop the forward flow of sub temperature milk in time when the heat source fails to provide the optimum temperature.

1.4 Fermented milk products 1.4.1 Yoghurt making 1.4.2 Basic practical requirement for production of Good quality

Yoghurt milk.

• Use high quality milk (must undergo basic quality testing)

• Use colostrum and mastitis free milk.

• Use milk free of starter culture inhibitors (chemical and drug residues)

• Use clean equipment, which should be sterilized with hot water.

• Always pasteurize the milk to the recommended temperatures.

• Use fresh starter cultures.

• Cool Yoghurt promptly and maintain cold chain during marketing.

1.4.3 Production of Yoghurt. - (Naivasha Recipe).

• You require good quality milk. • Ensure you have good starter culture.

• Filter the milk to remove physical dirt.

• Pasteurize the milk at 80 - 85oC for 30 minutes in a batch pasteurizer which can be a 50 litre can heated in hot water or improved wood fueled jiko.

• After pasteurization the milk should be cooled to 40 - 45 0C. Cooling may be done rapidly in a cold water basin or trough

• After cooling, inoculate the milk with 2 - 3% active starter culture. Stir well for 3-5 minutes to ensure uniform distribution of starter culture.

• Incubate at 40-45 0C for a period of 3- 5 hours.

• Check the coagulum. It should be compact without cracks or whey on top.

• Check the acidity. It should be 0.8 - 0.9% lactic acid or pH 4.2 - 4.3.

• Cool the coagulum by placing cans in chilled water or store in a refrigerator for. 12hrs. this is essential in preventing over souring of yoghurt. It also improves consistency and viscosity as well as full yoghurt flavour development.

• Break the coagulum and stir well to homogenise the curd to a smooth consistency. You may add sugar and flavourings at this stage. To minimise contamination sugar may be added towards the end of the pasteurisation process i.e. when the milk is still hot.

• Pack the finished product in retail containers for marketing.

1.4.4 Processing Steps in Commercial Yogurt Production: • Adjust Milk Composition and Blend Ingredients

Milk composition may be adjusted to achieve the desired fat and solids content. Often dry milk is added to increase the amount of whey protein to provide a desirable texture. Ingredients such as stabilizers are added at this time.

• Pasteurize Milk The milk mixture is pasteurized at 85°C for 30 minutes or at

95°C for 10 minutes. A high heat treatment is used to denature the whey (serum) proteins.

This allows the proteins to form a more stable gel, which prevents separation of the water during storage.

The high heat treatment also further reduces the number of spoilage organisms in the milk to provide a better environment for the starter cultures to grow.

Yogurt is pasteurized before the starter cultures are added to ensure that the cultures remain active in the yogurt after fermentation to act as probiotics; if the yogurt is pasteurized after fermentation the cultures will be inactivated.

Homogenize The blend is homogenized to mix all ingredients thoroughly and

improve yogurt consistency.

Cool Milk The milk is cooled to 42°C to bring the yogurt to the ideal growth

temperature for the starter culture.

Inoculate with Starter Cultures The starter cultures are mixed into the cooled milk.

Hold The milk is held at 42°C until pH 4.5 is reached. This allows the

fermentation to progress to form a soft gel and the characteristic flavor of yogurt. This process can take several hours.

Cool The yogurt is cooled to 7°C to stop the fermentation process.

Add Fruit & Flavors and sweetener Fruit and flavors and sweeteners are added at different steps

depending on the type of yogurt. For set style yogurt,

the fruit is added in the bottom of the cup and then the inoculated yogurt is poured on top and the

Yogurt is fermented in the cup. For Swiss style

The fruit is blended with the fermented, cooled yogurt prior to packaging.

1.4.5 Mala

How to make mala (Naivasha recipe) Use good quality milk, i.e. free from antibiotics and

preservatives, not adulterated.

If making sweetened cultured milk, add sugar at the rate of 20 to 25 kg per 500 liters (40 to 50 g per 1 litre).

Heat the milk to 92 to 95°C for 3 to 5 minutes or 85°C for 30 minutes or just bring to the boil.

Cool to 22 to 25°C (warm room temperature).

Inoculate with a commercial fermented milk culture (Mesophilic type) or mix with a small amount of fermented milk.

Incubate at 22 - 25°C (warm room temperate) for 16 to 18 hours.

Cool to 20°C (just cool to the touch) in 30 minutes.

In case of flavored cultured milk, add flavor and color.

Stir until smooth.

Pack at 20°C.

Refrigerate for 10 to 12 hours to help recover thickness lost during stirring.

Distribute for consumption and/or sale.

1.4.6 Butter

1.4.6.1 Butter

Butter is obtained by separation of the milk and subsequent churning of the cream. It contains a minimum of 80% butterfat. Butter can be made from fresh or sour cream. One litre of cream makes 300 to 400 g butter.

1.4.6.2 How to make butter (Naivasha recipe)If the cream is fresh:

Heat the cream to 800C to 90°C Cool it quickly, such as in running water, to 18°C Ripen by adding 50 ml (3 tablespoons) of sour butter milk or

Mesophilic starter culture. Stir this into the cream. Cover container and leave for 24 hours at 18°CChurning:

Half fill a churn with sour cream Churn with regular movement until the pieces of butter are as big

as peas and the buttermilk looks watery. Do not let the pieces of butter become one large lump

If there are no pieces of butter after 30 minutes, change the temperature by adding cold or warm water then churn again.

Churning may take 15 to 60 minutes - the time depends on the weather conditions, type of churn, fullness of the churn and fat content of the milk

Carefully remove the pieces of butter from the lid and side with clean cold water. The water with butter will float on top of the butter milk.

Pour off the butter milk through a coarse sieve.

Washing:

Wash the butter to remove butter milk. The more butter milk you remove the better the butter

Half fill the churn with clean cold water. Churn for at least 10 minutes Use a skimmer to remove the pieces of butter floating on the water

or wash the butter in a sieve Sieve the butter and butter milk, put the butter milk on one side,

turn the butter over while washing with clean cold water. Do not let the butter become one large lump.

Salting: Salt according to taste - 10g per kg of butter. Leave it overnight.

Kneading: Work (knead) the following day to improve the structure and quality Wash the work table with clean water Work the butter with a dump wooden spoon or a dump roller until it

has a smooth surface and you can see no more drops of water. As you work, remove any water.

Storage: Store butter in a cool place, in a pot or wrapped in a greaseproof

paper or aluminium foil Sprinkle a little salt on the surface of butter in a pot; this

prevents fungus. You can freeze butter but it becomes rancid quickly after defrosting

Divide the butter into many small parts and defrost only what you need

Do not freeze salted butter; it easily becomes fatty or oily and smells fishy

If you keep butter for too long it tastes rancid and develops fungus.

1.5 Ghee

Ghee is a class of clarified butter that originated in India and is commonly used in South Asian (Indian, Bangladeshi, Nepali, Sri Lankan, and Pakistani) cuisine and ritual.

Ghee can be defined as a pure clarified fat exclusively obtained from milk, cream or butter, by means of processes involving application of heat at atmospheric pressure, which results in the almost total removal of moisture and solid nonfat and which gives the product a characteristic flavor and physical structure and texture.

Ghee is a concentrated milk fat that is widely used in tropical regions of the world, especially in South Asian countries

1.5.1 Traditional ghee Traditionally, ghee is produced both on the domestic scale by first

converting milk into curd by fermentation process (Lactobacilli), churning curd to produce butter and subjecting butter to heat clarification to yield the final product.

Clarification by heat is done either on an open fire or in a steam-jacketed hemispherical kettle.

During initial heating of butter, extensive frothing takes place, which must be controlled to avoid losses associated with boil-over.

1.5.2 Uses Ghee is primarily used for domestic culinary purposes it may be incorporated into confectionery products, used to garnish food, or fed to children for therapeutic

purposes

1.5.3 Production of ghee

Ghee is typically prepared by heating cream or butter (from cows, buffaloes, camels, goats, or sheep) to a sufficiently high temperature at which it is held until most of the moisture has evaporated.

The high temperature produces carbonyls (aldehydes and ketones), lactones, and Free Fatty Acids , which confer a characteristic flavor (varies between locales) while improving shelf life by destroying bacteria, inactivating enzymes, and forming reducing compounds

Over - heating, however, may lead to charring of milk solids - not - fat, discoloration, and even loss of desirable volatile flavor compounds.

1.5.4 Commercial process Typically, in larger scale commercial production of ghee,

fresh or cultured cream is heated to 115 ° C in stainless – steel steam - jacketed vessels with continuous agitation until caramelisation produces a golden brown color.

When butter is the starting material, it is usually first heated to 60 ° C and then transferred as a liquid into the steam - jacketed stainless - steel ghee boiler, where it is heated with continuous agitation to 90 ° C

Heating to a higher temperature may be carried out to develop a desirable color and flavor in the final product.

The use of ripened milk, cream, or butter has been shown to produce an enhanced flavor in the ghee compared to the use of uncultured raw materials, and this is thought to be due to transfer of flavor metabolites such as free fatty acids and carbonyls from the aqueous phase of the original cultured source.

1.5.5 Packing and shelf life Ghee is generally packed into metal cans with a lacquered inner

surface, although laminated pouches have also been used as a cheaper alternative.

The shelf life of ghee is affected by its degree of unsaturation, but may be extended by storing a low – moisture product in opaque containers at a low temperature to reduce autoxidation.

1.5.6 Preference A good grainy texture due to the formation of large milk fat crystals is

an important quality attribute of ghee; this can be encouraged by seeding liquid ghee with a small quantity of ghee grains.

Ghee color and flavor are source and process dependent and tend to be determined by regional consumer preference.

1.6 Cheese

1.6.1 Cheese making involves a number of main stages that are common to most types of cheeses.

1.6.2 The cheese milk is pre-treated, possibly pre-ripened after addition of a bacteria culture appropriate to the type of cheese, and mixed with rennet.

1.6.3 Basic steps in cheese making1.6.3.1 Pasteurization

Before the actual cheese making begins, the milk usually undergoes pre-treatment designed to create optimum conditions for production.

Pasteurization must be sufficient to kill bacteria capable of affecting the quality of the cheese, e.g. coliforms, which can cause early “blowing” and a disagreeable taste. Regular pasteurization at 72 – 73°C for 15 – 20 seconds is most commonly applied.

1.6.3.2