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Yoghurt, yoghurt drink manufacturing app
Yoghurt, yoghurt drink manufacturing app guides employees through culturing, coagulation, mixing, and flavoring of yoghurt and yoghurt products in the yoghurt manufacturing process. Full yoghurt quality control, inventory, yoghurt food safety, recalls and audits.

Yoghurt, yoghurt drink manufacturing app

Yoghurt manufacturing process

Yoghurt, yoghurt drink manufacturing app
Yoghurt, yoghurt drink manufacturing app
  • Yogurt is made from milk cultured with live bacteria.
  • Yogurt is consumed in a variety of ways, including Greek yogurt, drinkable yogurt, and frozen yogurt.
  • The use of pasteurized milk is a key barrier to foodborne pathogen transmission in yogurt products. Raw milk can contain pathogens such as Escherichia coli, Salmonella spp., and Campylobacter jejuni. The acidity of yogurt is another barrier to foodborne illness. There is evidence of E. coli 0157:H7 exhibiting acid-tolerant properties, but this pathogen is readily destroyed via pasteurization.
  • Yogurt products have previously been associated with fungal disease.

Introduction

Yogurt has been a staple food product for numerous cultures throughout the world dating back many thousands of years. In the Middle East, primitive herdsman began carrying milk in containers made from intestinal gut lining, which they discovered could help extend the life of milk products because contact with the intestinal fluids of the containers caused the milk to curdle and sour, preserving it for an extended period. Other than drying, this was historically the only safe method of preserving milk.

Modern yogurt production involves culturing milk with live bacteria. The bacteria produce lactic acid which coagulates the milk proteins, making yogurt thick and slightly sour in flavor. The bacterial cultures required for producing yogurt are Streptococcus thermophilus and Lactobacillus bulgaricus. About 80% of all yogurt manufactured in the U.S. contains an additional culture called Lactobacillus acidophilus, and many commercial yogurt products also contain Bifidobacterium bifidum or Lactobacillus casei because of their potential health benefits.

Over the millennia, a multitude of health benefits have been attributed to eating yogurt. As for back as 6000 BCE, Indian Ayurvedic medicine made reference to the positive health benefits linked to yogurt consumption. Yogurt has been used in the treatment of everything from a variety of gastrointestinal maladies to sunburn relief. In the early 20th century, it was even sold in pharmacies as a medicine. Today, yogurt is promoted as a healthy “probiotic” food. The benefits of incorporating probiotic foods such as yogurt into the diet have been widely documented, and there is emerging research to suggest yogurt may have positive implications for improved gastrointestinal health and overall immune function.

Yogurt can be consumed directly, but it is also commonly used to make dips and dressings and is used as a lower-calorie substitute in cooking. Drinkable yogurt and frozen yogurt are also widely consumed yogurt products.

Types of Yogurt

The U.S. Food and Drug Administration (FDA) regulates and inspects commercial yogurt products. The FDA also sets the following guidelines for labeling yogurt:

  • Regular yogurt must be no less than 3.25% fat and contain no less than 8.25% milk solids.
  • Low fat yogurt must be between 0.5 to 2% fat and contain no less than 8.25% milk solids.
  • Non-fat yogurt must be less than 0.5% fat and contain no less than 8.25% milk solids.

Other terms used to describe yogurt are based on differences in processing:

Yoghurt, yoghurt drink manufacturing app
Yoghurt, yoghurt drink manufacturing app
  • Set (equivalent to sundae or fruit-on-the-bottom): This is the firmest type of yogurt. During processing, the yogurt is set in a container and is left undisturbed. Fruit can be added to the bottom of the container so that, when turned upside down, it resembles a sundae.
  • Swiss (equivalent to stirred, custard, or blended): Most commercial yogurts are Swiss style. After the yogurt is set, it is stirred and dispensed into secondary containers, making it less firm than set yogurt. Fruit can also be stirred in to produce flavor varieties.
  • Liquid or drinkable: Liquid yogurt has milk, fruit, and/or fruit syrups added for increased fluidity and flavor. The pH of yogurt is raised when milk is added, so the shelf life of drinkable yogurt is generally only 4–10 days.
  • Yogurt cheese or strained yogurt: Yogurt is strained to remove liquid whey, resulting in a thick, creamy, concentrated product.
  • Frozen yogurt: To make frozen yogurt, regular yogurt is mixed with a pasteurized ice cream mix of milk, cream, and sugar. Other ingredients, such as stabilizers, fruit, and flavors are blended together and then the mixture is frozen. In some cases, frozen yogurt contains live bacteria; the bacteria become dormant when cooled, but regain activity post-ingestion due to the warm body temperature.
  • Greek yogurt: Greek yogurt contains about twice the protein and half as much carbohydrates and sodium as regular yogurt. During processing, the yogurt is strained three times, as opposed to two times with regular yogurt, which yields the higher protein content and creamier texture. There are also low-fat and fat-free options for Greek yogurt.
  • Lite or light: Yogurt that has 50% less fat or one-third fewer calories than regular yogurt is considered light.

Foodborne Outbreaks

In 2013, an FDA investigation into complaints of gastrointestinal illness found that commercial yogurt products sold by the brand Chobani had been contaminated with the fungi Mucor circinelloides. Symptoms, including vomiting, nausea and diarrhea, were reported by more than 200 consumers who had ingested the associated yogurt products. The company voluntarily pulled the products connected to the reported illnesses from the market. The risk linked to fungal pathogens is not well understood, but M. circinelloides may cause spoilage in yogurt, and it poses a particular risk to the immunocompromised.

Yogurt (along with ice cream) was one of the vehicles of infection named in a 2007 outbreak of Hepatitis A which was determined to have been spread by a food-handler in a Minnesota restaurant. Fifteen people were reported ill and six were hospitalized; no deaths were reported. A Norovirus outbreak involving frozen yogurt and ice cream occurred in 2004 during a school fundraiser in Arizona. Norovirus was determined to be the source of the illnesses after an employee who had handled the machine tested positive. 53 fundraiser attendees reported being ill; no one was hospitalized, and no deaths were reported.

Interestingly, yogurt is often recommended as a natural aid in returning gut after contracting a foodborne illness.

To contribute to the Yogurt Foodborne Outbreaks section, please follow this link: https://fsi.colostate.edu/suggest-a-topic/

Production

U.S. yogurt production in 2017 totaled 4.5 billion pounds at 170 processing plants. New York leads the nation in yogurt production, accounting for 15.7% of the total amount of yogurt produced in the United States. California is the second largest producer of yogurt.

The production of yogurt requires only two ingredients: milk and live cultures. However, producers may also include, dry milk powder, stabilizers, fruit, and sweeteners.

Milk is the main ingredient used when making yogurt. It can be cream, whole, low-fat, or skim. Whole milk is used to make full-fat or regular yogurt, low-fat milk is used to make low-fat yogurt, and skim milk is used to make non-fat yogurt. In general, the higher the fat content of the milk, the smoother and creamier the yogurt will taste.

Live cultures are the second key ingredient in yogurt. There are two required cultures, Streptococcus thermophilus and Lactobacillus bulgaricus, and several optional ones.

Cream may be added to adjust the fat content of milk. Non-fat, dry milk powder is used to adjust the content of yogurt solids above the 8.25% minimum to achieve better body and texture. Stabilizers also function to improve body and texture as well as to increase firmness. They help keep fruit uniformly mixed in the yogurt and prevent separation of whey. Examples of stabilizers include alginates, gelatin, gums, pectins, and starch.

Sugar, honey, and artificial sweeteners may be used to reduce the naturally sour flavor of yogurt. Fruit, fruit syrups, and pie filling are also optional and can either be mixed in with yogurt or added to the top or bottom of the yogurt.

Processing

Pasteurization: In order to prevent deactivation of the bacterial cultures needed in yogurt production, milk is pasteurized at 185°F for 30 minutes or 203°F for 10 minutes prior to the addition of the cultures. The high heat also denatures the whey proteins, which allows the yogurt to form a more stable gel. Lastly, pasteurization effectively kills disease-causing bacteria.

Adjusting Milk Composition and Blending Ingredients: At this point, stabilizers are added to the mixture, as are sweeteners if a less tart yogurt is desired. The nonfat dry milk powder is also added before heating to prevent coagulation of the milk proteins.

Homogenization: Not all yogurts are homogenized. If this step is taken, the ingredients are mixed well to ensure a more stable consistency.

Heating: The milk is then heated to 200°F for 10–20 minutes, depending on the desired thickness of the yogurt. Holding it longer will result in a thicker yogurt.

Cooling and Inoculation: The mixture is then cooled rapidly to 112–115°F. At this point, the warm mixture is inoculated with the live bacterial culture.

Incubation: The mixture is incubated for 4–7 hours at 105–115°F. The bacteria used in making yogurt are thermophilic and this is their optimal temperature range; they are killed above 130°F and do not grow well below 98°F. Yogurt will become firm when a pH of 4.6 is reached. Incubating the mixture any longer will result in an increased acidity and more sour taste.

Cooling: When the desired pH is reached, the yogurt is cooled to around 45°F to end the fermentation process.

Addition of Fruit and Flavors: For set style yogurt, fruit is added to the bottom of the cup and the inoculated yogurt is placed on top of the fruit prior to fermentation. For Swiss style yogurt, fruit is mixed with the yogurt after the fermentation and cooling steps. The yogurt is then packaged; at which point, it should be refrigerated at 40°F or lower.

Food Safety

The acidity of yogurt acts as a barrier to bacteria growth, as does the high temperature achieved during the yogurt-making process. However, milk must be pasteurized beforehand to sufficiently kill disease-causing pathogens such as E. coli 0157:H7, which may be acid tolerant.

It is essential that all equipment and workspaces used in the yogurt-making process remain clean and sanitized to prevent the addition of unwanted bacteria to the yogurt.

The FDA requires that yogurt be made with live cultures, but some yogurts are heat treated so that the final product contains no active cultures. The label should specify what microorganisms are present, and in what amount in terms of colony-forming units (CFUs), as well as the known health benefits associated with the particular strains used. The label should also disclose the expiration or use-by date, serving size suggestion, company name, and proper storage of the product. Regardless of the use-by date, yogurt with visible signs of microbial growth or off-odors should be discarded immediately.

The shelf life of yogurt is 10–21 days. For liquid yogurt, the shelf life is 4–10 days and for yogurt cheese the shelf life is 7–14 days when refrigerated at 40°F. Yogurt can also be frozen for several months, but this may alter its texture.

Consumption

In 2017, per capita consumption of yogurt in the U.S. was 13.7 pounds. Domestic consumption peaked in 2014/2015 at 14.9 pounds per capita. Although yogurt consumption in the United States has continued to rise over the past two decades, the per capita consumption is dwarfed by Sweden’s annual 62.8 pounds per person. Research by the NPD Group reports that Americans between the ages of 18–34 are driving the increase in yogurt consumption in comparison to the older generations. In recent years, the health benefits of yogurt (particularly the recognition of probiotics) has encouraged a higher consumption of yogurt and the incorporation of yogurt into many more food products. Yogurt has been introduced into a wider variety of products, including fast food establishment menus, toothpastes, beauty products, and even pet foods. In the 2006-2007 Foodnet Population Survey Atlas of Exposures, 43.3% of the survey cohort reported eating fresh or flavored store-bought yogurt within the past seven days.

Information on keeping yogurt fresh and safe to eat can be found at FoodKeeper App.

Nutrition

The health benefits associated with yogurt consumption are plentiful, and there is ongoing research suggesting yogurt may contribute more to overall health than is currently known. All types of this fermented dairy product are a nutrient-rich source of calcium, potassium, and protein, and yogurts that have been fortified with vitamin D and/or probiotics have additional health benefits.

Probiotics are live microorganisms that develop a symbiotic relationship with the host when administered in the proper amount. Lactic acid bacteria that survive in the gut are often used as probiotics. This includes Lactobacillus rhamnosus, L. casei, L. acidophilus, and Bifidobacterium lactis, among others. The bacteria acquire nutrients and energy from the food people eat and, in return, help maintain a healthy gut microbiota. Research suggests this may promote immune function, improve mental health, and protect against cognitive impairment. It may also lower the risk of some chronic diseases, such as cancer, high blood pressure, obesity, and diabetes. Different strains of bacteria confer different benefits, which may be specified on the product label.

Gastrointestinal Health: Consuming probiotics is associated with a reduced severity and duration of diarrhea in children with acute infectious diarrhea, in those taking antibiotics, and in those with lactose intolerances. There is also evidence that probiotic consumption may be helpful in managing the symptoms of irritable bowel syndrome (IBS) and reducing relapses of ulcerative colitis. Some probiotics inhibit the growth of Helicobacter pylori, which is associated with ulcers and cancer of the stomach. The role of probiotics in preventing traveler’s diarrhea is being investigated.

Immune Health: Researchers have demonstrated that consuming probiotics can decrease the incidence of upper respiratory infections in adults and reduce cold and flu-like symptoms in children (resulting in higher attendance in preschool and daycare). There is also evidence that consuming yogurt may lower the incidence of yeast infections.

Emerging Research: Changes in the gut microbiota may occur with obesity and type II diabetes. There is potential for probiotics to play a role in the prevention of obesity and diabetes, but more research is needed. There is also a new field of research devoted to studying the link between the consumption of certain probiotics and mental health. A recent study showed that probiotics may reduce anxiety and stress, but further research is needed to confirm these findings.

References

  1. Dairy Products Profile. (n.d.). Retrieved from https://col.st/MyXCZ
  2. Foodborne Illness Outbreak Database – Sponsored by MarlerClark. (n.d.). Retrieved from https://col.st/vHGbV
  3. Foodborne Illness Outbreak Database – Sponsored by MarlerClark. (n.d.). Retrieved from https://col.st/Bo8xx
  4. Lee, S. C., Billmyre, R. B., Li, A., Carson, S., Sykes, S. M., Huh, E. Y., … Heitman, J. (2014, August 29). Analysis of a Food-Borne Fungal Pathogen Outbreak: Virulence and Genome of a Mucor circinelloides Isolate from Yogurt. Retrieved from https://col.st/UaNob
  5. Mauro, Machado, & Rachel. (2015, July 11). History of yogurt and current patterns of consumption. Retrieved from https://col.st/Sa461
  6. U.S. yogurt per capita consumption, 2018. (n.d.). Retrieved from https://col.st/jzIp4

Yogurt Production

This page describes the production of yogurt and includes the legal Yogurt Definitions, Ingredients, Bacterial Cultures, and General Manufacturing Procedure.

Yogurt Definitions

Yogurt is a fermented milk product that contains the characteristic bacterial cultures Lactobacillus bulgaricus and Streptococcus thermophilus. All yogurt must contain at least 8.25% solids not fat. Full fat yogurt must contain not less than 3.25% milk fat, lowfat yogurt not more than 2% milk fat, and nonfat yogurt less than 0.5% milk. The full legal definitions for yogurt, lowfat yogurt and nonfat yogurt are specified in the Standards of Identity listed in the U.S. Code of Federal Regulations (CFR), in sections 21 CFR 131.200, 21 CFR 131.203, and 21 CFR 131.206, respectively.

The two styles of yogurt commonly found in the grocery store are set type yogurt and swiss style yogurt. Set type yogurt is when the yogurt is packaged with the fruit on the bottom of the cup and the yogurt on top. Swiss style yogurt is when the fruit is blended into the yogurt prior to packaging.

Ingredients

The main ingredient in yogurt is milk. The type of milk used depends on the type of yogurt – whole milk for full fat yogurt, lowfat milk for lowfat yogurt, and skim milk for nonfat yogurt. Other dairy ingredients are allowed in yogurt to adjust the composition, such as cream to adjust the fat content, and nonfat dry milk to adjust the solids content. The solids content of yogurt is often adjusted above the 8.25% minimum to provide a better body and texture to the finished yogurt. The CFR contains a list of the permissible dairy ingredients for yogurt.

Stabilizers may also be used in yogurt to improve the body and texture by increasing firmness, preventing separation of the whey (syneresis), and helping to keep the fruit uniformly mixed in the yogurt. Stabilizers used in yogurt are alginates (carageenan), gelatins, gums (locust bean, guar), pectins, and starch.

Sweeteners, flavors and fruit preparations are used in yogurt to provide variety to the consumer. A list of permissible sweeteners for yogurt is found in the CFR.

Bacterial Cultures

The main (starter) cultures in yogurt are Lactobacillus bulgaricus and Streptococcus thermophilus. The function of the starter cultures is to ferment lactose (milk sugar) to produce lactic acid. The increase in lactic acid decreases pH and causes the milk to clot, or form the soft gel that is characteristic of yogurt. The fermentation of lactose also produces the flavor compounds that are characteristic of yogurt. Lactobacillus bulgaricus and Streptococcus thermophilus are the only 2 cultures required by law (CFR) to be present in yogurt.

Other bacterial cultures, such as Lactobacillus acidophilus, Lactobacillus subsp. casei, and Bifido-bacteria may be added to yogurt as probiotic cultures. Probiotic cultures benefit human health by improving lactose digestion, gastrointestinal function, and stimulating the immune system.

General Manufacturing Procedure

The following flow chart and discussion provide a general outline of the steps required for making yogurt. For a more detailed explanation see the literature references by Staff (1998), Tamime and Robinson (1999), Walstra et al. (1999) and the website by Goff, www.foodsci.uoguelph.ca/dairyedu/yogurt.html.

General Yogurt Processing Steps

1. Adjust Milk Composition & 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.

2. Pasteurize Milk

The milk mixture is pasteurized at 185°F (85°C) for 30 minutes or at 203°F (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.

3. Homogenize

The blend is homogenized (2000 to 2500 psi) to mix all ingredients thoroughly and improve yogurt consistency.

4. Cool Milk

The milk is cooled to 108°F (42°C) to bring the yogurt to the ideal growth temperature for the starter culture.

5. Inoculate with Starter Cultures

The starter cultures are mixed into the cooled milk.

6. Hold

The milk is held at 108°F (42°C) until a 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.

7. Cool

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

8. Add Fruit & Flavors

Fruit and flavors 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 yogurt the fruit is blended with the fermented, cooled yogurt prior to packaging.

9. Package

The yogurt is pumped from the fermentation vat and packaged as desired.

Yoghurt Yogurt Manufacturing and Production

Yogurt (also spelled yogourt or yoghurt)
Yogurt is a usually dairy product, which is made by blending fermented milk with various permitted ingredients that provide flavor and color.

The non daiy alternative market for yogurt is growing rapidly with a variety of non dairy proteins and fats, as raw materials and taste / texture improves then these products will grow in popularity due to the increasing veganism globally coupled with negative press re global warming and also lactose intolerance.

Raw Materials

Yogurt is made with a variety of ingredients including milk, proteins, fats, sugars, stabilizers, emulsifiers, fruits, flavors and bacterial cultures

Yogurt is going through a rapid period of change with new raw materials being marketed with superpowers such as the ability to kill yeasts and moulds. Care should be take when using these new mix formulations as manufacturers do not always fully declare the ingredients for protectionist reasons. If it is not in their ingredients then it is not going to be in yours but it will be detectable if tested for and as testing becomes easier, quicker and cheaper then this testing will be done. It is only a matter of time before yet another class action suit emerges with major manufacturers and retailers giving the industry generally a bad name for their bad practices. If it is in it then declare it!.

The milk used for yogurt production should be good quality and tested antibiotic free otherwise the antibiotics in the milk can kill the starter cultures. The process of making yogurt includes modifying the composition of and pasteurizing the milk at a high temperature (90C) and holding at that temperature for a prolonged time (5minutes); fermenting at warm temperatures with the set temperature optimised for the yogurt cultures selected; cooling; adding fruit, sugar, and other ingredients

Yogurt mix formulation

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 centrifugation to separate fat from milk.

The skimmed milk can be standardised for solids using a filtration plant but due to capital cost most manufacturers simply ass skimmed milk powder of protein powder.

Yoghurt, yoghurt drink manufacturing app
Yoghurt, yoghurt drink manufacturing app

From the separator, the fat standardiesd milk is pumped to a storage tank (usually agitated, insulated and or chilled) and tested for fat and total solids content. For stirred yogurt manufacture, the solids content of the milk is usually increased to about 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, other ingredients. 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 yogurt by reducing the tendency for it to separate on storage. Yogurt mix should have a minimum SNF of 12% to increase the viscosity and also to increase the resistance to "wheying off" (Increased proteing content = increased viscosity in the final product as it is the proteins that are integral to the formation of the coagulum) (Casein in particular) This increased SNF can be achieved by Evaporation of skimmed milk to give a skimmed milk concentrate or simply by the addition of skimmed milk powders or milk protein powders or concentrates. Recent advances in UF and RO give more options for ingredients

The choice of raw materials will greatly affect the quality of the finished product.


  • Type of milk - cow, buffalo, sheep etc
  • Yogurt Milk standardisation - standardize to the desired the fat content
  • Yogurt Additives - Fruit, stabilizers, emulsifiers, preservatives etc refer to Codex Alimentarius for permitted additives
  • Choice of starter culture - bulk or innoculated freeze dried, mixed strain etc Bulk usually 2% of mix volume
  • Yogurt culture preparation - Hygiene critical
  • Design of the yogurt process plant - batch, continuous etc
  • Heat treatment - dependant upon many factors 10°c to 95°c for 15 seconds to 25 minutes
  • Incubation - temperature matched to starter strains, usually 40° c to 45° c until 1% Lactic acid
  • Homogenisation - 200+ bar with two stage homogenisation preferred.
  • Cooling to between 5°c and 7°c
  • Addition of fruit and packing

Pasteurization and homogenization

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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. The milk is homogenized and the fat globules in the 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. The heat treatment of the milk prior to fermentation is generally considered essential in commercial manufacturing. The presence of unknown numbers of unknown organisms in the raw milk would make the fermentation too unreliable and unpredictable for commercial operations. In order to ensure that the flavour, aroma and texture of the product is optimised the growing conditions for the "starter culture" must be as near perfect as possible.

To ensure that the "starter culture" has least competition from other organisms the milk is heat treated to kill undesireable organisms in the milk.

The heat treatment also has a physio-chemical effect on the proteins and other additives in the mix.

The heating may be necessary for some of the ingredients to achieve the required state to form gels and protein lattice that lead to the products final viscosity and texture.

The inoculation and fermentation usually takes place in sealed hygienic stainless steel vessel. The temperature will be monitored and maintained at the optimum for the starter culture throughout the fermentation. The levels of lactic acid is measured and monitored throughout the fermentation and the fermentation is stopped by rapid cooling at the desired level of acidity. Too long or too short a fermentation will produce a product that is inferior in either flavour texture. Too long a fermentation will give other organisms the chance to become established, with the associated risks of "off" flavours and smells.

Fermentation

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.

The lactic acid level is used to determine when the yogurt is ready. The acid level is measured 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

Various styles of Yogurt

Yoghurt is usually classified into the following groups

Set Yoghurt

This type of yoghurt is incubated and cooled in the final package and is characterised by a firm "jelly" like texture. Set yogurt is usually a very low solids content yogurt and is popular in some low income countries like Ethipoia where price is important to the mass population, Despite the low solids (12% with zero fat content) a good quality set yogurt is a very refreshing product and can be very moreish whilst keeping the costs at their lowest possible. The downside for a set yogurt is that it requires careful handling and distribution. Roads with lots of potholes can result in a loss of / damage to the SET of the set yogurt. The process requires double handling and incubation in the yogurt pot at est 44° C for about 5 hours before moving to a air cooled store - rapid ambient reducing to about 25° C followed by blast chilling to less than 5° C. Rapid chilling is important to stop the bacteria rapidly reproducing and causing wheying off. Some liquid whey on the top is acceptable and this should be either poured off or mixed back in by the consumer depending on their preference. Fruit is not normally added to set yogurt but flavours and colours can be added.

Stirred yoghurt

This type of yoghurt is incubated in a tank and the final coagulum is "broken" by stirring prior to cooling and packing. The texture of a stirred yoghurt will be less firm than a set yoghurt. There is usually a slight reformation of the coagulm after the yoghurt has been packed

Drinking Yoghurt.

This type of yoghurt is very similar to stirred yoghurt, having the coagulum "broken!" prior to cooling. In a drinking yoghurt the agitation used to "break" the coagulum is severe. Little if any reformation of the coagulum will reoccur after packing.

Frozen Yoghurt.

Frozen yogurt requires a different recipe to yogurt and usually consists of a thin yogurt blended with a high solids ice cream base mix - for technical assistance with this contact jw@dairyconsultant.co.uk

Freezing is achieved by pumping through a freezer in a fashion similar to ice cream. The texture of the finished product is mainly influenced by the freezer.

Concentrated yoghurt

This type of yoghurt is inoculated and fermented in the same manner as a stirred yoghurt. Following the "breaking" of the coagulum the yoghurt is concentrated by boiling off some of the water, this is often done under vacuum to reduce the temperature required. Heating of low pH yoghurt can often lead to protein being totally denatured and producing rough and gritty textures. This is often called strained yoghurt due to the fat that the liquid that is released from the coagulum upon heating used to be "strained" off in a manner similar to making soft cheese.

Quarg or Quark
This is usually classified as a soft ripened cheese but I woul classify it as a high solids yogurt.
This is a higher solids yogurt using mesophillic cultures lower incubation temperatures but longer incubation time or Thermophilic Cultures with a higher temperature and lower incubation time.
The yogurt was traditionally strained using muslin bags hung over the vat overnight and then packed the next morning
Today thereare new options with centrifugal separation or nano filtration to remove the whey rapidly and increase efficiency and consistency.

Yoghurt, yoghurt drink manufacturing app
Yoghurt, yoghurt drink manufacturing app



Icelandic Skyr
This is a higher solids yogurt (focus on protein) using mesophillic cultures lower incubation temperatures but longer incubation time or Thermophilic Cultures with a higher temperature and lower incubation time.
The yogurt was traditionally strained using muslin bags hung over the vat overnight and then packed the next morning
Today thereare new options with centrifugal separation or nano filtration to remove the whey rapidly and increase efficiency and consistency.

Other Variants
You can design a yogurt / fermented soft cheese or something in between to meet your Unique Selling Point (USP) and market demand.
You might design a product with low fat, low sugar and high protein with a marketing emphasis on physical fitness or weight loss.
You could design a product with high fat for those not worried by weight but want something really nice tasting, an indulgent treat.
There are many options to suit all tastes and price ranges.
The yogurt production process should be kept as simple as possible and it may be difficult to navigate the equipment options, what you need and what you dont need as equipment companies are there to sell their process and extoll it's benefits like additional yield, more consistency etc.

Whey-less yogurt - no whey yogurt process
Greek style yogurt, Greek style Yoghurt, Quark, Quark, Skyr etc can be formulated to absorb all the water / whey and eliminate the by product whey and also eliminate the separation step which can have a high capital cost as well as operational costs.
When manufacturing a non fat Quarg produt then the protein content is usually reduced to eliminate the dry / slightly gritty texture due to lack of fat.

Flavoured yoghurt

Yoghurt with various flavours and aromas have become very popular. The flavours are usually added at or just prior to filling into pots. Common additives are fruit or berries, usually as a puree or as whole fruit in a syrup. These additives often have as much as 50% sugar in them, however with the trend towards healthy eating gaining momentum, many manufacturers offer a low sugar and low fat version of their products. Low or no sugar yoghurts are often sweetened with saccharin or more commonly aspartame. The use of "fruit sugars" in the form of concentrated apple juice is sometimes found as a way of avoiding "added sugar" on the ingredients declaration, this tends to be a marketing ploy and has no real added benefit. Typical composition of a commercial fruited yoghurt

Fruited yogurt


Fruit or cereal corner yogurt


Vegetable yogurts


Factors that alter the quality of yoghurt

Bacteriophages

Bacteriophages are a group of virus that attack the yoghurt starter organisms, a whole range of defects can be attributed to the action of these bacteriophage. Bacteriophage normally referred to just as "phage" are the most likely cause of long or never-ending incubations. Large manufacturers that have laboratory facilities to check incoming milk will often eliminate the possibilities of other starter inhibiting substances but "phage" is always a risk. "Phage" are usually found in the drains and floor gullies of a dairy producing any cultured product, poor hygiene and a lack of general housekeeping increase the risk. Cheese manufacturing and the subsequent whey handling are prime sources of "phage".

Starter culture

The starter culture is the term generally applied to the organisms used to ferment a cultured product, (cheese, yoghurt, Kefir, ). The organisms selected for this purpose need to produce the desired affect in the product, (although you could use a cheese starter in a yoghurt fermentation, the result would not be yoghurt). For normal commercial yoghurt the starter must be capable of fermenting lactose and producing lactic acid, little if any carbon dioxide is required and the flavour and aroma must be clean and fresh. Traditionally when a suitable starter organism had been found a large quantity would be grown in a suitable nutrient medium (traditionally milk, but commercial blends of nutrients are now available), and small quantities would be used to inoculate each new batch of yoghurt. This technique with a main batch of starter culture is often referred to as using "bulk starter". The use of a bulk starter is becoming increasingly uncommon amongst commercial producers, mainly because of the risk of "phage" attack on the bulk starter, and the subsequent lost time while a new batch of starter organisms are prepared. A technique often referred to as DVI (Direct Vat Inoculation) is becoming the industry norm. DVI involves inoculating the yoghurt mix directly with a very large number of freeze dried starter organisms. The advantage of relative immunity to "phage" attack far outweigh the slightly longer incubation time required with this technique.

Fat %

The percentage of fat in the final yoghurt has a significant effect on the "mouthfeel", the normal range of fat content is from 0.5% to about 3.5%, however levels as low as 0% and as high as 10% are found in some speciality products.

In general the higher the fat level in the yoghurt the creamier and smoother it will feel in the consumers mouth. A considerable amount of work has been carried out by the commercial manufacturers to reproduce this "creamy mouthfeel" without the use of fat. There are now a number of very low fat yoghurts on the market that have this "creamy mouthfeel" and still offer the health benefits of a low fat diet.

The Dry Matter content.

The higher the dry matter (solids non milk fat) the firmer the yoghurt will be. Commercial manufacturers control the dry matter in their yoghurt to ensure consistency of production.

The normal methods used to standardise the dry matter content are:

  • Evaporation,
  • Addition of skimmed milk powder,
  • Addition of milk concentrate,
  • Addition of the ultra filtration retentate from skimmed milk,
  • Addition or whey powder,
  • Addition of sodium Caseinate powder.
  • Sugars and sweeteners Disaccharide sugars such as sucrose or monosaccharides such as glucose can be used alone or in conjunction to produce the sweetness level required. Levels of sugar greater than 10% should not be added to the yoghurt mix prior to the incubation, this is because the changes in osmotic pressure will adversely effect the starter culture. If higher levels of sugar addition are required then a means of adding the sugar after fermentation needs to be devised. The addition of sugar often improves the "body " and "mouthfeel" of a yoghurt.

Stabilisers

Hydrophilic colloids will bind water and consequently increase the viscosity of a yoghurt, they also help prevent the separation of whey from the yoghurt, a problem known as syneresis. The most beneficial quantity os stabiliser to add to a yoghurt mix has to be determined experimentally by each manufacturer. Too much stabiliser and the yoghurt can take on a rubbery texture, far too much stabiliser and the yoghurt can become a hard solid mass. A traditionally produced natural yoghurt will require no stabilisers to produce a firm, fine gel, however commercially produced yoghurt that has to be pumped, stirred, fruited and filled will often break down to a runny liquid without the addition of stabilisers. Pasteurised yoghurt will definitely need to be stabilised as the nature of the heat treatment will adversely affect any naturally formed gel. The mechanical handling of a yoghurt after its incubation has a significant effect on its final texture and viscosity, consequently the design of the equipment needs to reflect this. Common stabilisers are, gelatin, pectin, agar, starch. In quantities in the order of 0.1% to 0.5%.

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