Yogurt
Background
Yogurt is a dairy product, which is made by blending fermented milk with various ingredients that provide flavour and colour.
It is believed that yoghurt originated in Mesopotamia thousands of years ago. Evidence has shown that these people had domesticated goats and sheep around 5000 B.C. The milk from these animals was stored in gourds, and in the warm climate, it naturally formed a curd. This curd was an early form of yogurt. Eventually, a process for purposely producing yoghurt was developed.
While yoghurt has been around for many years, it is only recently (within the last 30-40 years) that it has become popular. This is due to many factors including the introduction of fruit and other flavourings into yoghurt, the convenience of it as a ready-made break-fast food and the image of yoghurt as a low-fat healthy food.
Manufacturers have responded to the growth in the yoghurt market by introducing many different types of yoghurt including low fat and no-fat, creamy, drinking, bio-yoghurt, organic, baby, and frozen. Traditional yoghurt is thick and creamy. It is sold plain and in a wide assortment of flavours. These are typically fruit flavours such as strawberry or blueberry however, newer, more unique flavours such as cream pie and chocolate have also been introduced.
Cereals and nuts are sometimes added to yoghurts. Yoghurt makers also sell products with varying levels of fat. Low-fat yoghurt, which contains between 0.5% and 4% fat, is currently the best selling. Diet no-fat yoghurt contains no fat at all. It also contains artificial sweeteners that provide sweetness while still reducing calories. Creamy yoghurt is extra thick, made with whole milk and added cream. Drinking yoghurt is a thinner product, which has a lower solids level than typical yoghurt. Bio-yogurt is made with a different type of fermentation culture and is said to aid digestion. Yogurt that is made with milk from specially fed cows is called organic yoghurt. This type of yogurt is claimed to be more nutritious than other yoghurts. Other types of yoghurts include pasteurized stirred yoghurt that has extended shelf life, baby yoghurt made specifically for children, and frozen yoghurt.
The yoghurt itself has a generally aldehydic flavour, which is a result of the fermentation process. Since it is made from milk, yoghurt is rich in nutrients. It contains protein and vitamins and is a rich source of calcium. In fact, a small container of yoghurt contains as much calcium as a third of a pint of milk. In addition to these nutritional characteristics, yoghurt is also thought to have additional health benefits. One of the suggested benefits of yoghurt is that it acts as a digestive aid. In the body, it is thought that yoghurt can encourage the growth of beneficial bacteria in the gut. These organisms help to digest food more efficiently and protect against other, harmful organisms. Another health benefit of yoghurt is for people that are lactose intolerant. These people have difficulty digesting milk products however, they typically can tolerate yoghurt.
Raw Materials
In general, yoghurt is made with a variety of ingredients including milk, sugars, stabilizers, fruits and flavours, and a bacterial culture
When the milk arrives at the plant, its composition is modified before it is used to make yoghurt. This standardization process typically involves reducing the fat content and increasing the total solids. Once modification occurs, it is pasteurized to kill bacteria and homogenized to consistently disperse fat molecules.
(Lactobacillus bulgaricus). During fermentation, these organisms interact with the milk and convert it into curd. They also change the flavour of the milk giving it the characteristic yoghurt flavour of which acetaldehyde is one of the important contributors. The primary by-product of the fermentation process is lactic acid. The acid level is used to determine when the yoghurt fermentation is completed which is usually three to four hours. The suppliers of these yoghurt cultures offer various combinations of the two bacterial types to produce yoghurts with different flavours and textures.
To modify certain properties of the yoghurt, various ingredients may be added. To make yoghurt sweeter, sucrose (sugar) may be added at approximately 7%. For reduced-calorie yoghurts, artificial sweeteners are used. The cream may be added to provide a smoother texture. The consistency and shelf stability of the yoghurt can be increased by the inclusion of stabilizers such as food starch, gelatin, locust bean gum, guar gum and pectin. These materials are used because they do not have a significant impact on the final flavour. The use of stabilizers is not required, however, and some marketers choose not to use them to retain a more natural image for their yoghurt.
To improve taste and provide a variety of flavours, many kinds of fruits are added to yoghurt. Popular fruits include strawberries, blueberries, bananas, and peaches, but almost any fruit can be added. Beyond fruits, other flavourings are also added. These can include such things as vanilla, chocolate, coffee, and even mint. Recently, manufacturers have become quite creative in the types of yoghurt they produce using natural and artificial flavourings.
The Manufacturing Process
The general process of making yoghurt includes modifying the composition of and pasteurizing the milk; fermenting at warm temperatures; cooling it; and adding fruit, sugar, and other materials.
Modifying milk composition
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1 When the milk arrives at the plant, its composition is modified before it is used to make yoghurt. This standardization process typically involves reducing the fat content and increasing the total solids. The fat content is reduced by using a standardizing and a separator (a device that relies upon centrifugation to separate fat from milk). From the clarifier, the milk is placed in a storage tank and tested for fat and solids content. For yoghurt manufacture, the solids content of the milk is increased to 16% with 1-5% being fat and 11-14% being solids-not-fat (SNF). This is accomplished either by evaporating off some of the water or adding concentrated milk or milk powder. Increasing the solids content improves the nutritional value of the yoghurt, makes it easier to produce a firmer yoghurt and improves the stability of
The milk substance is fermented until it becomes yogurt. Fruits and flavourings are added to the yoghurt before packaging.
the yoghurt by reducing the tendency for it to separate on storage.
Pasteurization and homogenization
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2 After the composition of the solid is adjusted, stabilizers are added and the milk is pasteurized. This step has many benefits. First, it will destroy all the microorganisms in the milk that may interfere with the controlled fermentation process. Second, it will denature the whey proteins in the milk which will give the final yoghurt product a better body and texture. Third, it will not greatly alter the flavour of the milk. Finally, it helps release the compounds in milk that will stimulate the growth of the starter culture. Pasteurization can be a continuous or batch process. Both of these processes involve heating the milk to a relatively high temperature and holding it there for a set amount of time. One specific method for batch process pasteurization is to heat a large, stainless steel vat of milk to 185° F (85° C) and hold it there for at least 30 minutes.
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3 While the milk is being heat-treated, it is also homogenized. Homogenization is a process in which the fat globules in milk are broken up into smaller, more consistently dispersed particles. This produces a much smoother and creamier end product. In commercial yoghurt making, homogenization has the benefits of giving a uniform product, which will not separate. Homogenization is accomplished using a homogenizer or visualizer. In this machine, the milk is forced through small openings at high pressure and fat globules are broken up due to shearing forces.
Fermentation
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4 When pasteurization and homogenization are complete, the milk is cooled to between 109.4-114.8° F (43-46° C) and the fermentation culture is added in a concentration of about 2%. It is held at this temperature for about three to four hours while the incubation process takes place. During this time, the bacteria metabolize certain compounds in the milk-producing the characteristic yoghurt flavour. An important byproduct of this process is lactic acid.
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5 Depending on the type of yoghurt, the incubation process is done either in a large tank of several hundred gallons or in the final individual containers. Stirred yoghurt is fermented in bulk and then poured into the final selling containers. Set yoghurt, also known as French style, is allowed to ferment right in the container it is sold in. In both instances, the lactic acid level is used to determine when the yoghurt is ready. The acid level is found by taking a sample of the product and titrating it with sodium hydroxide. A value of at least 0.9% acidity and a pH of about 4.4 is the current minimum standards for yoghurt manufacture in the United States. When the yoghurt reaches the desired acid level, it is cooled, modified as necessary and dispensed into containers (if applicable).
Adding other ingredients
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6 Fruits, flavours, and other additives can be added to the yoghurt at various points in the manufacturing process. This is typically dependent on the type of yogurt being produced. Flavour in non-fruit yoghurts are added to the process milk before being dispensed into cartons. Fruits and flavours can also be added to the containers first, creating a bottom layer. The inoculated milk is then added on top and the carton is sealed and incubated. If the fruit is pasteurized, it can be added as a puree to the bulk yoghurt, which is then dispensed into containers. Finally, the fruit can be put into a special package, which is mixed with plain yoghurt upon consumption.
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7 The finished yoghurt containers are placed in cardboard cases, stacked on pallets, and delivered to stores via refrigerated trucks.
Quality Control
Milk products such as yoghurt are subject to a variety of safety testing. Some of these include tests for microbial quality, degree of pasteurization, and various forms of contaminants. The microbial quality of the incoming milk is determined by using a dye reaction test. This method shows the number of organisms present in the incoming milk. If the microbial count is too high at this point, the milk may not be used for manufacture.
Since complete pasteurization inactivates most organisms in milk, the degree of pasteurization is determined by measuring the level of an enzyme in the milk called phosphatase. Governmental regulations require that this test be run to ensure that pasteurization is done properly. Beyond microbial contamination, raw milk is subject to other kinds of contaminants such as antibiotics, pesticides or even radioactivity. These can all be found through safety testing and the milk is treated accordingly.
In addition to safety tests, the final yoghurt product is also evaluated to ensure that it meets the specifications set by the manufacturer for characteristics such as pH, rheology, taste, colour, and odour. These factors are tested using various laboratory equipment such as pH meters and viscometers and also human panellists.
The Future
The future of yoghurt manufacturing will focus on the development of new flavours and longer-lasting yoghurts. The introduction of new flavours will be driven by consumer desires and new developments by flavour manufacturers. The suppliers of the bacterial cultures are researching that hints at the development of uniquely flavoured yoghurts. By varying the types of organisms in the cultures, yoghurt is produced much faster and lasts longer than conventional yoghurt.
Additionally, the nutritional aspects of yoghurt will be more thoroughly investigated There is some evidence that has shown consumption of yoghurt has a beneficial antibiotic effect. It has also been shown to reduce the incidence of lactose intolerance and other gastrointestinal illnesses. Other purported benefits of yoghurt include the reduction of cholesterol, protection against certain cancers, and even boosting the immune system. The research is still not complete on these benefits however, these factors will likely be important in the continued market growth of yoghurt.