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Useful microbes – b6

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USEFUL MICROBES – B6 By Daisy Cartledge
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Page 1: Useful microbes – b6

USEFUL MICROBES – B6By Daisy Cartledge

Page 2: Useful microbes – b6

YOGURT - PREPARATION 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 stability of the yogurt by reducing the tendency for it to separate on storage. [1]

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YOGHURT - PASTEURISATION 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 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. [1]

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YOGURT - HOMOGENISATION 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. [1]

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YOGURT – INCUBATION AND SAMPLING During incubation 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. During this time, the bacteria metabolizes certain compounds in the milk producing the characteristic yogurt flavour. An important by product of this process is lactic acid. 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. 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. [1]

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YOGURT – ADDING AND PACKAGING Fruits, flavours, colourings, 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. Flavour in non-fruit yogurts 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 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. [1]

The finished yogurt containers are placed in cardboard cases, stacked on pallets, and delivered to stores via refrigerated trucks. [1]

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YOGURT – 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. [1]

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YOGURT - TESTING 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, colour, and odour. These factors are tested using various laboratory equipment such as pH meters and viscometers and also human panellists. [1]

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YOGURT - BACTERIA Yogurt is produced through the fermentation of milk

by lactic acid bacteria, usually lactobacillus bulgarius and Streptococcus thermophilus. [2]

Fresh milk contains sugars and some bacteria. The bacteria feed on the sugars in the milk. The main sugar in milk is called lactose. Lactose is converted into lactic acid by bacterial fermentation, the increased acidity sours and thickens the milk. [2]

Bacterial Fermentation can be summarised by the following word equation - Lactose Lactic Acid [2]

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FERMENTATION Fermentation is the name given to the process where a

sugar (glucose)solution containing yeast is turned into alcohol (ethanol). [3]

The balanced equation for fermentation is: Glucose ethanol  + carbon dioxide C6H12O6(aq)  2C2H5OH(aq)  + 2CO2(g) The carbon dioxide gas bubbles out of the solution into the

air leaving a mixture of ethanol and water. Fermentation must be carried out in the absence of air to make ethanol. This is called anaerobic conditions. If air is present, ethanoic acid is made instead of ethanol. [3]

Fermentation will not happen without yeast. Yeast is a microorganism containing an enzyme which acts as a catalyst. Fermentation works best in warm conditions (between 18 and 35 °C) and at a neutral or acidic pH (between 4 and 7). [3]

[3]

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DISTILATION Distillation is a method of increasing the alcohol

concentration of fermentation products. Most products are a mixture of alcohol, fruit extracts and water. [4]

The boiling point of alcohol is ~80ºC, water is 100ºC. When heated, the alcohol boils away first and can be collected by cooling it in a condenser. [4]

The condenser works by circulating cold water round a central glass tube which cools down alcohol vapour. This condenses to form liquid alcohol. The basic principle relies on the different boiling points of alcohol and water.“Drinking” alcohol is a member of the alkanol family and is called ethanol (C2H5OH.) [4]

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DISTILLATION – HOW IT’S DONE

[4]

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DISTILLATION – LIMITATIONS AND ADVANTAGES The ability of yeast cells to convert sugar into carbon

dioxide and alcohol is down to enzymes. Several enzymes are involved each does its step in the process. The final step is zymase reduction which takes the end product of the other enzymes (acetaldehyde/glycerol), and turns this into good old ethyl alcohol. However, high concentrations alcohol actually destroys enzymes and kills the yeast cell.

Different strains of yeast can tolerate different concentrations of alcohol.. Brewers yeast cannot withstand much beyond 5 or 6% Alcohol by volume. Wine yeast is more tolerant at a range of 10-15% Specially cultured strains of yeast with the correct environment can withstand alcohol levels up to 21% alcohol. [5]

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THE SUGARS IN BEER AND WINE The sugars for beer-making come from boiling barley

in water. Hops are added to adjust the flavour of the beer. [6]

The sugars for wine-making come from grape juice. Different varieties of grapes are used to produce wines with different flavours. Wine contains a higher proportion of ethanol than beer does, because grape juice contains a higher concentration of sugars than barley in water. [6]

[7] [8]

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STAGES OF WINEMAKING Extract the flavour and aroma from the base

ingredients by chopping, crushing, pressing, boiling or soaking them. [9]

Add sugar, acid, nutrients, and yeast to the fermentation media to achieve the proper ratio and ferment, in a primary fermentation vessel (crock, jar or polyethylene pail) at 70-75 degrees Fahrenheit. [9]

Strain the liquid from the pulp, put the liquid into a secondary fermentation vessel (a carboy or jug), fit a trap (airlock) on the mouth of the bottle, and ferment at 60-65 degrees Fahrenheit until bubbling stops. [9]

Siphon the wine off the sediments into another clean secondary fermentation vessel. Reattach the trap. Repeat after a month again and again before bottling. [9]

When wine is clear and all fermentation has stopped, siphon into wine bottles and cork securely. [9]

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STAGES OF BEER MAKING Pale malt extract and hops are boiled together with

water to sterilize the extract and release the bittering qualities of the hops. [10]

The hot mixture (called wort) is cooled to room temperature and siphoned to a fermenter where it is combined with additional water. Once the mixture drops to room temperature, yeast is added to start the fermentation process. Cleanliness and sanitation are very important since the wort can be easily infected by bacteria in this state. An airlock is used during fermentation. [10]

Once fully fermented, it is siphoned to another container to prepare for bottling. Here priming sugars are mixed with the beer. The beer is siphoned into bottles. [10]

Once bottled it will age and the yeast will ferment the remaining sugar you added and create carbon dioxide. [10]

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ENZYME ACTIVITY – EFFECT OF PH Most enzymes have an optimum activity of about pH 7 as this

is close to the pH level of the blood. [11]

Some special enzymes have a different optimum pH, especially in the stomach. [11]

[11]

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ENZYME ACTIVITY – EFFECT OF TEMPERATURE This graph shows that enzyme activity increases as the

temperature increases. There is an optimum (best) temperature (~40ºC.) [11]

Above 50ºC, the heat destroys (denatures) the enzyme. [11]

[11]

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BIBLIOGRAPHY1. http://www.madehow.com/Volume-4/Yogurt.html2. h

ttp://www.bbc.co.uk/bitesize/standard/biology/biotechnology/living_factories/revision/6/

3. http://www.gcsescience.com/rc17-fermentation-yeast-alcohol.htm 4. http://

www.bbc.co.uk/bitesize/standard/chemistry/plasticsandothermaterials/carbohydrates/revision/6/

5. http://www.yobrew.co.uk/fermentation.php6. http://

www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/designerproducts/foodanddrinkrev1.shtml

7. http://www.123rf.com/photo_24409471_fresh-green-hops-and-barley-isolated-on-white.html

8. http://www.medicalnewstoday.com/articles/271156.php 9. http://winemaking.jackkeller.net/basics.asp10. http://beersmith.com/blog/2009/01/10/how-to-brew-beer-5-steps-for-making-b

eer-at-home-part-1/

11. http://www.bbc.co.uk/bitesize/standard/chemistry/plasticsandothermaterials/carbohydrates/revision/7/


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