How yogurt is made – manufacture, making, used, composition, product, machine, Raw Materials

Table of Contents1 Background 2 Raw Materials 3 The Manufacturing Process 3.1 Modifying milk composition 3.2 Pasteurization and homogenization 3.3 Fermentation 3.4 Adding other ingredients 4 Quality Control 5 The Future 6 Where to Learn More 6.1 Books Background Yogurt is a dairy product, which is made by blending fermented […]

Background

Yogurt is a dairy product, which is made by blending fermented milk with
various ingredients that provide flavor and color. Although accidentally
invented thousands of years ago, yogurt has only recently gained
popularity in the United States.

It is believed that yogurt 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 yogurt was developed.

While yogurt 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 flavorings into
yogurt, the convenience of it as a ready-made break-fast food and the
image of yogurt as a low fat healthy food.

Manufacturers have responded to the growth in the yogurt market by
introducing many different types of yogurt including low fat and no-fat,
creamy, drinking, bio-yogurt, organic, baby, and frozen. Traditional
yogurt is thick and creamy. It is sold plain and in a wide assortment of
flavors. These are typically fruit flavors such as strawberry or
blue-berry however, newer, more unique flavors such as cream pie and
chocolate have also been introduced. Cereals and nuts are some-times added
to yogurts. Yogurt makers also sell products with a varying level of fat.
Low fat yogurt, which contains between 0.5% and 4% fat, is currently the
best selling. Diet no-fat yogurt contains no fat at all. It also contains
artificial sweeteners that provide sweetness while still reducing
calories. Creamy yogurt is extra thick, made with whole milk and added
cream. Drinking yogurt is a thinner product, which has a lower solids
level than typical yogurt. 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 yogurt. This type of
yogurt is claimed to be more nutritious than other yogurts. Other types of
yogurts include pasteurized stirred yogurt that has extended shelf life,
baby yogurt made specifically for children, and frozen yogurt.

The yogurt itself has a generally aldehydic flavor, which is a result of
the fermentation process. Since it is made from milk, yogurt is rich in
nutrients. It contains protein and vitamins and is a rich source of
calcium. In fact, a small container of yogurt contains as much calcium as
a third of a pint of milk. In addition to these nutritional
characteristics, yogurt is also thought to have additional health
benefits. One of the suggested benefits of yogurt is that it acts as a
digestive aid. In the body, it is thought that yogurt 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 yogurt is for people that are lactose
intolerant. These people have difficulty digesting milk products however,
they typically can tolerate yogurt.

Raw Materials

In general, yogurt is made with a variety of ingredients including milk,
sugars, stabilizers, fruits and flavors, and a bacterial culture


When the milk arrives at the plant, its composition is modified
before it is used to make yogurt. 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 a curd. They also change the flavor of the milk giving it the
characteristic yogurt flavor of which acetaldehyde is one of the important
contributors. The primary byproduct of the fermentation process is lactic
acid. The acid level is used to determine when the yogurt fermentation is
completed which is usually three to four hours. The suppliers of these
yogurt cultures offer various combinations of the two bacterial types to
produce yogurts with different flavors and textures.

To modify certain properties of the yogurt, various ingredients may be
added. To make yogurt sweeter, sucrose (sugar) may be added at
approximately 7%. For reduced calorie yogurts, artificial sweeteners such
as aspartame or saccharin are used. Cream may be added to provide a
smoother texture. The consistency and shelf stability of the yogurt can be
improved 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 flavor. The use of
stabilizers is not required however, and some marketers choose not to use
them in order to retain a more natural image for their yogurt.

To improve taste and provide a variety of flavors, many kinds of fruits
are added to yogurt. Popular fruits include strawberries, blueberries,
bananas, and peaches, but almost any fruit can be added. Beyond fruits,
other flavorings 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 yogurt they produce using natural and
artificial flavorings.

The Manufacturing

Process

The general process of making yogurt 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

  • 1 When the milk arrives at the plant, its composition is modified before
    it is used to make yogurt. This standardization process typically
    involves reducing the fat content and increasing the total solids. The
    fat content is reduced by using a standardizing clarifier 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 yogurt 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
    yogurt, makes it easier to produce a firmer yogurt and improves the
    stability of

    The milk substance is fermented until it becomes yogurt. Fruits and flavorings are added to the yogurt before packaging.

    The milk substance is fermented until it becomes yogurt. Fruits and
    flavorings are added to the yogurt before packaging.

    the yogurt by reducing the tendency for it to separate on storage.


Pasteurization and homogenization

  • 2 After the solids composition 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 yogurt product better
    body and texture. Third, it will not greatly alter the flavor 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.
  • 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 yogurt making,
    homogenization has the benefits of giving a uniform product, which will
    not separate. Homogenization is accomplished using a homogenizer or
    viscolizer. In this machine, the milk is forced through small openings
    at a high pressure and fat globules are broken up due to shearing
    forces.


Fermentation

  • 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 metabolizes certain
    compounds in the milk producing the characteristic yogurt flavor. An
    important byproduct of this process is lactic acid.
  • 5 Depending on the type of yogurt, the incubation process is done either
    in a large tank of several hundred gallons or in the
    final individual containers. Stirred yogurt is fermented in bulk and
    then poured into the final selling containers. Set yogurt, 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 yogurt 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 are the current minimum standards for
    yogurt manufacture in the United States. When the yogurt reaches the
    desired acid level, it is cooled, modified as necessary and dispensed
    into containers (if applicable).


Adding other ingredients

  • 6 Fruits, flavors, and other additives can be added to the yogurt at
    various points in manufacturing process. This is typically dependent on
    the type of yogurt being produced. Flavor in non-fruit yogurts are added
    to the process milk before being dispensed into cartons. Fruits and
    flavors 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 yogurt, which is then dispensed into containers. Finally,
    the fruit can be put into a special package, which is mixed with plain
    yogurt upon consumption.
  • 7 The finished yogurt containers are placed in cardboard cases, stacked
    on pallets, and delivered to stores via refrigerated trucks.

Quality Control

Milk products such as yogurt 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 yogurt product is also evaluated to
ensure that it meets the specifications set by the manufacturer for
characteristics such as pH, rheology, taste, color, and odor. These
factors are tested using various laboratory equipment such as pH meters
and viscometers and also human panelists.

The Future

The future of yogurt manufacturing will focus on the development of new
flavors and longer lasting yogurts. The introduction of new flavors will
be driven by consumer desires and new developments by flavor
manufacturers. The suppliers of the bacterial cultures are conducting
research that hints at the development of uniquely flavored yogurts. By
varying the types of organisms in the cultures, yogurt is produced much
faster and lasts longer than conventional yogurt.

Additionally, the nutritional aspects of yogurt will be more thoroughly
investigated There is some evidence that has shown consumption of yogurt
has a beneficial antibiotic effect. It has also been shown to reduce the
incidence of lactose intolerance and other gastro-intestinal illnesses.
Other purported benefits of yogurt 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 yogurt.

Where to Learn More


Books

Helferich, W. and D. Westhoff.

Yogurt: All About It,

1980.

Hui, Y.H., ed.

Dairy Science and Technology Handbook.

New York: Wiley VCH, 1992.

Robinson, R.K. “Snack Foods of Dairy Origin.” In

Snack Food.

Edited by Gordon R. Booth. New York: Van Nostrand Reinhold, 1990, pp.
159-182.

Robinson, R.K and A.Y. Tamime. “Recent developments in yoghurt
manufacture.” In

Modern Dairy Technology.

Edited by B.J.F. Hudson. London: Elsevier Applied Science Publishers,
1986, pp 1-36.

Source Article

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