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Questions and Answers
Which process is used to obtain coffee beans from berries?
Which process is used to obtain coffee beans from berries?
What fermentation bacteria are involved in cocoa production?
What fermentation bacteria are involved in cocoa production?
What is the primary yeast used in brewing?
What is the primary yeast used in brewing?
Why must oxygen levels be kept low during fermentation?
Why must oxygen levels be kept low during fermentation?
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What is the primary sugar source used in wine production?
What is the primary sugar source used in wine production?
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What step in winemaking helps reduce unwanted yeasts?
What step in winemaking helps reduce unwanted yeasts?
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What is the role of Streptococcus thermophilus in yoghurt production?
What is the role of Streptococcus thermophilus in yoghurt production?
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What is the purpose of the malting process in beer production?
What is the purpose of the malting process in beer production?
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What is the primary difficulty in using barley as a sugar source for fermentation?
What is the primary difficulty in using barley as a sugar source for fermentation?
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Which of the following dairy products is produced through controlled fermentation of milk?
Which of the following dairy products is produced through controlled fermentation of milk?
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What evidence suggests that probiotics may not have significant effects on health?
What evidence suggests that probiotics may not have significant effects on health?
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Who initiated the 'Good Bacteria' theory and what was his contribution?
Who initiated the 'Good Bacteria' theory and what was his contribution?
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What is the primary function of Bifidobacteria in the human gut?
What is the primary function of Bifidobacteria in the human gut?
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What is the role of acetic acid bacteria in vinegar production?
What is the role of acetic acid bacteria in vinegar production?
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Which of the following is NOT a typical feedstock for distilled beverages?
Which of the following is NOT a typical feedstock for distilled beverages?
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What is the primary result of the curdling process in milk?
What is the primary result of the curdling process in milk?
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Which microorganism is commonly used to give Swiss cheese its characteristic flavor and gas bubbles?
Which microorganism is commonly used to give Swiss cheese its characteristic flavor and gas bubbles?
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What is the main carbohydrate found in milk that contributes to the fermentation process?
What is the main carbohydrate found in milk that contributes to the fermentation process?
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What process allows for the scaling up of ethanol production from various feedstocks?
What process allows for the scaling up of ethanol production from various feedstocks?
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Which ingredient is traditionally used in cheese making to promote curdling?
Which ingredient is traditionally used in cheese making to promote curdling?
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Which type of cheese is associated with Penicillium roqueforti?
Which type of cheese is associated with Penicillium roqueforti?
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What type of fermentation is involved in the production of Koji?
What type of fermentation is involved in the production of Koji?
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What role does salt play in the fermentation of sauerkraut?
What role does salt play in the fermentation of sauerkraut?
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Which microorganism is primarily responsible for the fermentation of dry sausages such as salami?
Which microorganism is primarily responsible for the fermentation of dry sausages such as salami?
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Which statement about the fermentation of soya beans is true?
Which statement about the fermentation of soya beans is true?
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What is one of the primary uses of fermentation in the food industry?
What is one of the primary uses of fermentation in the food industry?
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In the context of fermentation, which of the following describes the role of Lactobacilli in sauerkraut?
In the context of fermentation, which of the following describes the role of Lactobacilli in sauerkraut?
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Which of the following enzymes is most likely NOT related to the fermentation process in dairy products?
Which of the following enzymes is most likely NOT related to the fermentation process in dairy products?
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What characteristic feature is common in the fermentation of fish sauces used in Asian cuisine?
What characteristic feature is common in the fermentation of fish sauces used in Asian cuisine?
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What is the primary purpose of kilning in the malt-making process?
What is the primary purpose of kilning in the malt-making process?
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Which temperature range is suitable for the germination of malted grains?
Which temperature range is suitable for the germination of malted grains?
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What is the primary role of amylase during the mashing process?
What is the primary role of amylase during the mashing process?
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What effect do hops have during the brewing process?
What effect do hops have during the brewing process?
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What is the difference between top and bottom fermenting yeasts?
What is the difference between top and bottom fermenting yeasts?
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During boiling, what happens to the amylases in the wort?
During boiling, what happens to the amylases in the wort?
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In decoction mashing, what is the first temperature range used for protein rest?
In decoction mashing, what is the first temperature range used for protein rest?
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What initiates fermentation during the brewing process?
What initiates fermentation during the brewing process?
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Study Notes
Agricultural Microbiology - MICR20010
- Course code is MICR20010
- Course title is Agricultural Microbiology
- Instructor is Dr. Tadhg Ó Cróinín
- Practical MCQ exam results will be released this evening.
- Exam results are output as a percentage then converted to a letter grade using an alternative linear scale
- A+ is 95% and above to 100%
- The alternative linear scale is provided with the percentage ranges for each grade
Remaining Lectures
- Lecture 10: Microorganisms and Disease
- Lecture 11: The Immune System
- Lecture 12: Pathogenic Bacteria
- Lecture 13: Pathogenic Fungi and Viruses
- Lecture 14: Antibiotic Resistant Microorganisms
- Lecture 15: Microbiology in the Food Industry - The Fungi
- Lecture 16: Microbiology in the Food Industry - Fermentations
- Lecture 17: The Nitrogen Cycle
Fermentations - Food and Drink
- An ancient process that existed before the study of microbiology.
- Critical for the production of Beer, Wine, and various Dairy products
Fermentation Pathways
- Lactobacillus:
- Glucose → fructose diphosphate → 2 phosphoglyceric acid →2 pyruvic acid → 2 lactic acid
- Saccharomyces:
- Glucose → fructose diphosphate → 2 triose phosphate →2 pyruvic acid → alcohol + CO₂
Fermented Vegetables
-
Soya bean fermentation
- Koji: Aerobic fermentation with Aspergillus
- Moromi: Anaerobic fermentation with Tetragenococcus halophila
-
Sauerkraut
- Lactobacilli fermentation of shredded cabbage
- Salt prevents Gram-negative contaminants
Fermented Meat and Fish
- Various dry sausages (e.g., salami, pepperoni, bologna) use Staphylococcus, Pediococcus, Micrococcus, and Lactobacilli.
- Fish sauces are a variety of sauces and pastes in Asian cooking, sometimes using fish and shrimps, and salt, in sealed vessels to allow natural microflora (like S. carnosus and Staphylococcus piscifermentans) to work
Coffee and Cocoa
- Coffee (Coffea arabica):
- Wet or dry process to obtain beans from berries
- Wet process uses indigenous fungi and bacteria, secreting proteolytic enzymes, followed by lactic acid bacterial fermentation.
- Cocoa (Theobroma cacao):
- Pods are opened to remove beans.
- A sequence of fermentations (involving yeasts, lactic acid and acetic acid bacteria) occurs before the beans are processed further.
Brewing
- Ancient use of fermentation, a very important economic activity
- Primarily Saccharomyces cerevisiae but occasionally Zymomonas.
- Zymomonas produces African palm wine or Mexican pulque
The Basics (Brewing)
- Aerobic pathway is preferred by yeast, so need to reduce oxygen to promote fermentation and alcohol production.
- CO₂ produced must be allowed to escape.
- Glucose as a substrate provides the starting material
Winemaking
- Grapes are the source of sugar
- Fructose + Glucose are used as sugars, and natural acidity is important
- Soil, climate, grape variety, pressing method (primary and secondary fermentations) influence wine characteristics.
- Red wine is made with skins containing anthocyanins
Making the "Must"
- Grapes are crushed mechanically or by hand (feet)
- Fermentation is driven by indigenous yeasts or starter cultures.
- Fermentation rate is impacted by temperature, pH, initial sugar levels, and yeast strain
The Fermentor
- Typically wooden fermentors, but currently mostly stainless steel.
- Cooling is necessary to manage heat produced (1.3°C per 10g/L)
- Unwanted yeasts are controlled by SO₂
- Starter culture of S. cerevesiae added
- Secondary fermentation may occur
- Clarifying agents and filtration are used, followed by bottling
Cider
- Cider production is similar to winemaking
- Additional sugar may be added to help the reaction
- Apple juice already has a high sugar content
The Problem with Barley
- Barley contains 65% starch as a sugar source
- Starch needs to be broken down into simpler sugars for easier utilization
Malting Process - Partial Germination
- Enzymes are generated (amylases) and substrates for fermentation are created during the malting of the grain.
- Green malt, created after five days of germination, undergoes kiln drying and partial cooking using hot air.
- Malt is preserved using kilning
Making Malt - The Steps
- Soak or steep barley for 2 days at 10-16°C.
- Occasionally aerate.
- Germinate for 3-5 days at 16-19°C on malting floors, a process that requires aeration and mechanical turning.
- Subsequently kiln dry by heating to 50-60°C and then 80-110°C to stop enzyme development, prevent enzyme denaturation, and add flavour
Making Wort
- Malted grains supply both enzymes and substrate for fermentation, but additional adjuncts are useful.
- Starch conversion into simple sugars
- Wort is prepared (mashing) as a glucose source.
Mashing - Making the Wort
- Allows endogenous and added substrates to be acted upon by enzymes.
- Various types of mashing are used, such as decoction mashing.
- In decoction mashing, the process begins at 35-40°C, with some of the mash being boiled, and reintroduced to incrementally increase the mash temp (and sometimes repeated) for protein rest
- In infusion mashing, a specific temperature is maintained throughout the process
But What is Happening?
- Amylase and other enzymes break starch down into fermentable sugars.
- Proteases also break down cell walls to enable starch access.
- If enzyme activity is limiting, commercial enzymes can be added.
- The sweet wort is then boiled.
Wort is Boiled
- Amylases are inactivated.
- Starch breakdown is stopped.
- Alpha acids and oils from hops to kill microbes and give flavour to the wort
- Sugars are caramelized
Hops
- Bitter herb grown on a vine
- Stabilizes flavour as well as providing preservative in brewing.
- Hop oils contain alpha acids for a bitter taste and a preservative element
Brewing (Wort Addition)
- Wort is prepared, and yeast is added
- Fermentation is allowed to occur for approximately 3 days
- Afterwards, a further 10 days are allowed for fermentation in the production of beer
Brewing: Types of Brewing Yeasts
- Top fermenting yeasts
- Remain distributed throughout the wort.
- They are carried up to the top by CO₂ production.
- Ales utilize 14-23°C fermentation temperatures.
- S. cerevisiae is commonly used.
- Bottom fermenting yeasts
- Settle to the bottom.
- 6-12°C fermentation temperatures are used.
- Saccharomyces carlsbergensis is commonly used (a larger yeast compared to other yeasts.)
Differentiation of an ale yeast from a lager yeast
- S. cerevisiae and S. carlsbergensis can both grow at 27°C, but S. cerevisiae can grow at 37°C. S. carlsbergensis cannot grow at 37°C
Brewing (Post-Fermentation)
- Allow yeast to settle at the bottom
- Siphon off beer into bottles, allow to age further.
Distilled Beverages
- Alcohol boils at 78°C
- Malt (e.g., Whiskey)
- Wine (e.g., Brandy)
- Molasses (e.g., Rum)
- Grains/potatoes (e.g., Vodka)
- Colour is affected by barrel aging
Economic Importance
- Largest consumer of alcohol in Europe.
- Brew history in the region.
- Local breweries are significant economic contributors
Scaling up Ethanol production
- 50 Billion liters are produced from the fermentation of various feedstocks.
- Ethanol serves as an industrial solvent and a biofuel.
Vinegar
- Not only a condiment, but also an important preservative.
- Solution containing greater than 4% acetic acid.
- Different sources (e.g., America-cider, Europe-Wine, Britain-Malt) utilize different production approaches focusing on different substrates.
- Acetic acid bacteria are crucial for vinegar production.
Vinegar Production
- Changing ethanol to vinegar involves the conversion of ethanol to acetic acid using acetic acid bacteria.
- Distilled vinegars are commonly produced by this method.
- Production involves a recirculation tube, pump, wood grating, collecting chamber, beechwood shavings, oxidation air intakes, and cooling coils.
Fermented Dairy products
- Milk is 87% water
- Milk proteins: whey and casein.
- Fat-flavor components.
- Carbohydrates: lactose.
- Vitamins
Microorganisms Involved in Dairy Fermentations
- Lactococci, Lactobacilli, and S. thermophilus.
- Can be single or mixed cultures.
- Other microorganisms can be used to influence flavor and texture
Curdling Milk
- Acidification of milk coagulates milk proteins (curd).
- This can be achieved through a pure starter culture or a mixed culture.
- Rennet, an enzyme mix that promotes curdling (traditionally calf chymosin, now often fungal proteases).
Dairy Products (Cheese Production)
- The production process involves pasteurization, standardization, and filtration.
- Rennet is used for curdling.
- Curds are drained of whey and poured into molds.
- Salting, pressing, and ripening processes occur.
A Second Inoculum
- After salting the curd, a second microbial inoculum is added.
- Different inoculants:
- Swiss cheese - Propionibacterium freundenreichii (flavor, gas bubbles)
- Blue cheeses - Penicillium roqueforti (inoculated into cheese)
- Camembert - Penicillium camemberti (characteristic rind and flavor).
Huge Variation in Cheeses
- A wide variety of cheeses exist due to differences in the production processes
Dairy Products (Other)
- Other types of fermented milk products include yogurt, buttermilk, and sour cream.
- Streptococcus thermophilus is important in yogurt production.
Yogurt
- Controlled fermentation of milk is essential.
- Lactobacillus bulgaricus and Streptococcus thermophilus are used for production.
- Pasteurization, addition of Streptocuccus thermophilus, Lactobacillus bulgaricus, incubation (at 42-45 C) generates yogurt.
- Symbiotic event leads to protein breakdown and release of peptides by L. bulgaricus, acid production (folic and formic acid) used by L. bulgaricus to synthesize purines by S. thermophilus
The Probiotic World
- "Good bacteria" theory.
- Elie Metchnikoff (1845-1916) began the study.
- Pasteur institute in France created "la Ferment”.
- Minoru Shirota (1930s) isolated L. casei Shirota from human feces.
- Yakult now produces these probiotics.
The Probiotic World (Additional Notes)
- Bifidobacteria and lactic acid bacteria are commensals in the gut (16 and 3% of normal flora).
- They are thought to be effective in treating antibiotic-induced diarrhea, IBS, IBD, and possibly neurological conditions.
- More study is needed to definitively prove probiotic benefits
In Summary
- Fermentations are crucial in industrial microbiology.
- They are critical in the dairy and beverage industries, particularly in cheese, yogurt, probiotic, beer, and wine production.
- S. cerevesiae is important for beer production.
- Acetic acid bacteria are essential for vinegar production.
Final Lecture
- Final lecture on Friday, covering the Nitrogen Cycle and Environmental Microbiology.
- A study guide will be provided on how to prepare for the exam.
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Description
Test your knowledge on the various fermentation processes used in food production, including coffee, cocoa, wine, beer, and yoghurt. This quiz covers the role of specific bacteria and yeasts, as well as critical steps in each fermentation process. Perfect for students of food science and microbiology.
