CHAPTER 20 : MILK
Milk is the most nutritive, naturally occurring, beverage in the world. Also, it is a great raw material or starting ingredient for a world of culinary delights. Especially in India it has a terrific and tremendous cultural, social and economic significance.
Milk comes from a variety of sources and across the world a lot of products which are non-dairy in nature are often referred to as milk. The objective of this enquiry is to view this as hospitality and food professionals; and get, the various details otherwise unknown to those who do not attend catering college.
Milk is home to 9 major nutrients, viz;
• Fat 2%
• Protein 8 grams
• Calcium 285 mg, which is 22% to 29%, the daily intake recommended of calcium for an adult
• Sugars (lactose)
• Saturated fatty acids
• Mono-unsaturated fatty acids
• Poly-unsaturated fatty acids
Pasteurization is typically associated with milk. Pasteurization typically uses temperatures below boiling since at very high temperatures milk, casein micelles will irreversibly aggregate (or "curdle").
There are three main types of pasteurization used today:
1. High Temperature/Short Time (HTST) and
2. Extended Shelf Life (ESL) treatment.
3. Ultra-high temperature (UHT or ultra-heat treated) is also used for milk treatment.
First suggested by Franz von Soxhlet in 1886, HTST pasteurised milk typically has a refrigerated shelf life of two to three weeks. In the HTST process, milk is forced between metal plates or through pipes heated on the outside by hot water, and is heated to 71.7 °C (161 °F) for 15–20 seconds. HTST pasteurization processes must be designed so that the milk is heated evenly, and no part of the milk is subject to a shorter time or a lower temperature.
In the ESL direct heating plant, the product is first regeneratively preheated to 70 °C – 85 °C and then heated to maximum 127 °C by direct steam injection. The milk is held at this temperature for approx. 3 seconds and is then cooled down to 70 °C - 85 °C in a flash cooler. To ensure the product is well stabilized, aseptic homogenization is carried out at a temperature of approx. 70 °C.As a result of these extremely short heating and cooling times at a high heating temperature, the direct process offers the advantage of top product quality.
UHT processing holds the milk at a temperature of 135 °C (275 °F) for a fraction of a second. When UHT treatment is combined with sterile handling and container technology; (such as aseptic packaging), it can even be stored unrefrigerated for 3–4 months.
Milk simply labelled "pasteurised" is usually treated with the HTST method, whereas milk labelled "ultra-pasteurised" or simply "UHT" has been treated with the UHT method.
Pasteurization may have been a response to the hazards and contamination issues that resulted from the newly emerging "industrialised" dairy industry. It's likely that, with the burgeoning growth of large-scale, longer-distance distribution networks, the rise of chain-store supermarkets, and the resulting impetus for larger-herd dairy operations and mechanised milking, there came a corresponding inability to preserve the quality and inherent bacterial-resistance qualities of fresh milk being marketed in a localised area.
Effectiveness of Pasteurization
Milk pasteurization has been subject to increasing scrutiny in recent years, due to the discovery of pathogens that are both widespread and heat resistant (able to survive pasteurization in significant numbers). Researchers have developed more sensitive diagnostics, such as real-time PCR and improved culture methods that have enabled them to identify pathogens in pasteurised milk. The HTST pasteurization standard was designed to kill 99.999% of the number of viable micro-organisms in milk. This is considered adequate for destroying almost all yeasts, mould, and common spoilage bacteria and also to ensure adequate destruction of common pathogenic heat-resistant organisms (including Mycobacterium tuberculosis, which causes tuberculosis and Coxiella burnetii, which causes fever).
Microfiltration is a process that partially replaces pasteurization and produces milk with fewer microorganisms and longer shelf life without a change in the taste of the milk. In this process, cream is separated from the whey and is pasteurized in the usual way, but the whey is forced through ceramic micro filters that trap 99.9% of microorganisms in the milk (as compared to 95% killing of microorganisms in conventional pasteurization). The whey is then recombined with the pasteurized cream to reconstitute the original milk composition.
Upon standing for 12 to 24 hours, fresh milk has a tendency to separate into a high-fat cream layer on top of a larger, low-fat milk layer. The cream is often sold as a separate product with its own uses; today the separation of the cream from the milk is usually accomplished rapidly in centrifugal cream separators. The fat globules rise to the top of a container of milk because fat is less dense than water. The smaller the globules, the more other molecular-level forces prevent this from happening.
The cream rises in cow's milk much more quickly than a simple model would predict: rather than isolated globules, the fat in the milk tends to form into clusters containing about a million globules, held together by a number of minor whey proteins. These clusters rise faster than individual globules can. The fat globules in milk from goats, sheep, and water buffalo do not form clusters so readily and are smaller to begin with; cream is very slow to separate from these milks.
In order to understand how centrifugal separation works, we shall follow the course of milk through a separator bowl. As milk flows into a rapidly revolving bowl it is acted upon by both gravity and the centrifugal force generated by rotation. The centrifugal force is 5000 to 10 000 times that of gravity, and the effect of gravity thus becomes negligible. Therefore, milk entering the bowl is thrown to the outer wall of the bowl rather than falling to the bottom. Milk serum has a higher specific gravity than fat and is thrown to the outer part of the bowl while the cream is forced towards the centre
of the bowl.
Milk is often homogenized, a treatment which prevents a cream layer from separating out of the milk. The milk is pumped at high pressures through very narrow tubes, breaking up the fat globules through turbulence and cavitations. A greater number of smaller particles possess more total surface area than a smaller number of larger ones, and the original fat globule membranes cannot completely cover them.
The exposed fat globules are briefly vulnerable to certain enzymes present in milk, which could break down the fats and produce rancid flavours. To prevent this, the enzymes are inactivated by pasteurizing the milk immediately before or during homogenization.
Homogenized milk tastes blander but feels creamier in the mouth than unhomogenized; it is whiter and more resistant to developing off flavours.
Creamline, or cream-top, milk is unhomogenized; it may or may not have been pasteurized. Milk which has undergone high-pressure homogenization, sometimes labelled as "ultra-homogenized," has a longer shelf life than milk which has undergone ordinary homogenization at lower pressures. Homogenized milk may be more digestible than unhomogenized milk.
Classification of milk
I. Based on fat content
• Whole milk
• Reduced-fat milk (2%)
• Low-fat milk (1%)
• Skimmed milk/non-fat milk
• Half & half
"Whole" milk refers to Creamline (unhomogenized) milk.
"Homogenized" milk refers to milk which is 3.25% butterfat (or milk fat).
There are also skim, 1%, and 2% milk fat milks.
A blended mixture of half cream and half milk is often sold in small quantities and is called half-and-half. Half-and-half is used for creaming coffee and similar uses.
II. TYPE (NON – DAIRY)
The term milk is also used for whitish non-animal substitutes such as soy milk, rice milk, almond milk, and coconut milk.
1. SOY MILK:
Soy milk (also called soya milk, soymilk, soybean milk, or soy juice) and sometimes referred to as soy drink/beverage is a beverage made from soybeans. A stable emulsion of oil, water, and protein, it is produced by soaking dry soybeans and grinding them with water.
Soy milk contains about the same proportion of protein as cow's milk: around 3.5%; also 2% fat, 2.9% carbohydrate, and 0.5% ash. Soy milk can be made at home with traditional kitchen tools or with a soy milk machine.
2. RICE MILK:
Rice milk is a kind of grain milk processed from rice. It is mostly made from brown rice and commonly unsweetened. The sweetness in most rice milk varieties is generated by a natural enzymatic process. Some rice milk kinds may nevertheless be sweetened with sugarcane syrup or other sugars.
3. ALMOND MILK:
Almond milk is a milky drink made from ground almonds. Unlike animal milk, almond milk contains no cholesterol or lactose. It can be used as a substitute for animal milk in many recipes, and is also completely vegan.
Commercial almond milk products such as brand Almond Breeze come in plain, vanilla, or chocolate flavours. They are often enriched with vitamins. It can also be made at home by combining ground almonds with water in a blender. Vanilla flavouring and sweeteners are often added. However, users should be cautious not to use bitter almonds, since the combination of bitter almonds and water releases cyanide.
4. COCONUT MILK
Coconut milk is a sweet, milky white cooking base derived from the meat of a mature coconut. The colour and rich taste of the milk can be attributed to the high oil content and sugars.
In Malaysia, Brunei and Indonesia coconut milk is called santan and in the Philippines it is called gata. In Thailand it is called ga-ti and used in many of the Thai curries. In Brazil, it is called leite de coco (literally, coconut milk). It should not be confused with coconut water (coconut juice), which is the naturally-occurring liquid found inside a coconut.
III. BY SOURCE:
1. Goats milk
Some goats are bred for milk, which can be drunk raw, although some people recommend pasteurization to reduce bacteria such as Staphylococcus aureus and Escherichia coli. If the strong-smelling buck is not separated from the does, his scent will affect the milk. Goat's milk is commonly processed into cheese, goat butter, ice cream,and other products.
Goat's milk can replace sheep's milk or cow's milk in diets of those who are allergic. However, like cow's milk, goat's milk has lactose (sugar), and may cause gastrointestinal problems for individuals with lactose intolerance.
Goat's milk naturally has small fat globules, which means the cream remains suspended in the milk, instead of rising to the top, as in raw cow's milk; therefore, it does not need to be homogenized.
2. Camel’s milk
Camel milk is a staple food of desert nomad tribes and is richer in fat and protein than cow milk. It is said to have many healthful properties. It is used as a medicinal product and as an aphrodisiac in Ethiopia.
Bedouins believe that the curative powers of camel milk are enhanced if the camel's diet consists of certain plants. Camel milk can readily be made into yogurt, but can only be made into butter or cheese with difficulty. Butter or yogurt made from camel milk is said to have a very faint greenish tinge.
Camel milk cannot be made into butter by the traditional churning method. It can be made if it is soured first, churned, and a clarifying agent added, or if it is churned at 24–25 °C (75–77 °F), but times vary greatly in achieving results. Until recently, camel milk could not be made into cheese because rennet was unable to coagulate the milk proteins to allow the collection of curds. The cheese produced from this process has low levels of cholesterol and lactose. The sale of camel cheese is limited owing to the low yield of cheese from milk and the uncertainty of pasteurization levels for camel milk which makes adherence to dairy import regulations difficult.
IV. BY FORM:
1. Condensed milk
Condensed milk, also known as sweetened condensed milk, is cow's milk from which water has been removed and to which sugar has been added, yielding a very thick, sweet product which when canned can last for years without refrigeration if unopened. The two terms, condensed milk and sweetened condensed milk, have become synonymous; though there have been unsweetened condensed milk products, today these are uncommon. Condensed milk is used in numerous dessert dishes in many countries,
2. Powdered milk
Powdered milk is a manufactured dairy product made by evaporating milk to dryness. One purpose of drying milk is to preserve it; milk powder has a far longer shelf life than liquid milk and does not need to be refrigerated, due to its low moisture content. Another purpose is to reduce its bulk for economy of transportation. Powdered milk and dairy products include such items as dry whole milk, non-fat dry milk, dry buttermilk, dry whey products and dry dairy blends.
3. Evaporated milk
Evaporated milk, also known as dehydrated milk, is a shelf-stable canned milk product with about 60% of the water removed from fresh milk. It differs from sweetened condensed milk, which contains added sugar. Sweetened condensed milk requires less processing since the added sugar inhibits bacterial growth.
The actual liquid portion of the product takes up half the space of fresh milk. When the non-liquid product is mixed with a proportionate amount of water, evaporated milk becomes the equivalent of fresh milk. This makes evaporated milk attractive for shipping purposes and can have a shelf life of months or even years, depending upon the brand. This made evaporated milk very popular before refrigeration as a safe and reliable substitute for perishable fresh milk that could be shipped easily to locations lacking the means of safe milk production or storage. Households in the western world use it most often today for desserts and baking due to its unique flavor. It is also used as a substitute for pouring cream, as an accompaniment to desserts, or (undiluted) as a rich substitute for milk.
4. INFANT FORMULA
Infant formula is a food manufactured to support adequate growth of infants under six months of age when fed as a sole source of nutrition]. The composition of infant formula is roughly based on a mother's milk at approximately one to three months postpartum. The most commonly used infant formulas contain purified cow's milk whey and casein as a protein source, a blend of vegetable oils as a fat source, lactose as a carbohydrate source, a vitamin-mineral mix, and other ingredients depending on the manufacturer. In addition, there are infant formulas using soya bean as a protein source in place of cow's milk (mostly in the United States and Great Britain) and formulas using protein reduced (hydrolyzed) into its component amino acids for infants who are allergic to other proteins. An upswing in breastfeeding has been accompanied by a deferment in the average age of introduction of other foods (such as cow's milk), resulting in increased use of both breastfeeding and infant formula between the ages of 3–12 months.
5. BAKED MILK:
Baked is a variety of boiled milk that has been particularly popular in Russia and Ukraine. It is made by cooking boiled milk on low heat for eight hours or more.
In rural areas, baked milk has been produced by leaving a jug of boiled milk in an oven for a day or for a night until it is coated with a brown crust. The stove in a traditional Russian log house (izba) was designed so as to "sustain varying cooking temperatures based on the placement of the food inside the oven".
Nowadays baked milk is produced on an industrial scale, as is soured or fermented baked milk, traditionally known as ryazhenka. Like scalded milk it is free of bacteria and enzymes, and so can be stored safely at room temperature for up to forty hours. Home-made baked milk was (and still is) used for preparing a range of cakes, pies, and cookies.
Lactose, the disaccharide sugar component of all milk must be cleaved in the small intestine by the enzyme lactase in order for its constituents (galactose and glucose) to be absorbed. The production of this enzyme declines significantly after weaning in all mammals. Consequently, many humans become unable to properly digest lactose as they mature. There is a great deal of variance, with some individuals reacting badly to even small amounts of lactose, some able to consume moderate quantities, and some able to consume large quantities of milk and other dairy products without problems. When an individual consumes milk without producing sufficient lactase, they may suffer diarrhoea, intestinal gas, cramps and bloating, as the undigested lactose travels through the gastrointestinal tract and serves as nourishment for intestinal micro flora who excrete gas, a process known as anaerobic respiration.
Lactose intolerance is a natural process and there is no reliable way to prevent or reverse it. Lactase is readily available in pill form, and many individuals can use it to briefly increase their tolerance for dairy products.