B6 - Brewing and Biofuels Flashcards
What is brewing? How is wine, beer and cider made?
Brewing is the production of alcoholic drinks by the process of fermentation. Yeast makes the alcohol by fermenting sugars found in plants, usually in the fruit or grain (seed).
• Wine is made from grapes.
• Beer and lager are made from malted barley.
• Cider is made from apples.
Describe and explain the process of brewing.
- Malting - this happens in beer- and lager-making. The barley seeds start to germinate (grow), which converts the starch stored in the seeds into sugar.
- Extracting the sugar - the plant material is either crushed or soaked in water to get the sugar out.
- Flavouring - wines get their flavour from the fruit juice used, while beers are avoured with hops, the female flowers of the hop plant, Humulus lupulus.
- Adding yeast - the container is sealed to prevent air and other microbes entering. The yeast can respire aerobically for a very short time, until any oxygen in the container is used up. This allows the yeast to reproduce. The liquid is kept warm.
- Fermentation - the culture quickly becomes anaerobic and the yeast starts to produce alcohol.If there is too much oxygen in the container, anaerobic respiration does not occur and vinegar is produced. This process happens in large stainless steel vats called fermenters. The mixture is kept at a constant temperature of 25–30°C, which gives the best rate of respiration to produce alcohol. This temperature also gives a better flavour.
- Extracting the wine and beer - the liquid is separated from the yeast cells. Usually the yeast is allowed to sink to the bottom to separate it out of the liquid. The liquid may need clarifying by a filtration process.
- Pasturing and packaging / bottling - the product is heated and quickly cooled to kill any remaining microbes. This gives the product a longer shelf life when stored in bottles.
Give the word and symbol equation for fermentation.
glucose (sugar) → ethanol (alcohol) + carbon dioxide
C6H12O6 → 2C2H5OH + 2CO2
Why is there a limit to the concentration of alcohol made?
Alcohol is toxic and eventually kills the yeast in the fermenter when it reaches a certain concentration. Some yeasts can tolerate more alcohol than others. This results in drinks with different alcohol contents:
• Beers and lagers usually contain 3–5% alcohol.
• Wines usually contain 11–12% alcohol.
How are spirits made?
To make spirits, the first step is fermenting plant material, similar to the production of beers and wines.
• Rum is made from sugar cane.
• Whiskey is made from malted barley.
• Vodka is made from potatoes.
How can spirits have 40% alcohol?
To increase the concentration of alcohol from the fermentation process, the liquid is distilled.
The liquid is placed in a large container, or still, and heated. The alcohol boils at a temperature of about 80°C, which is lower than the boiling point of water.
The alcohol rises up the column as a vapour, leaving the water behind. The vaporised alcohol passes along a collecting arm, and cools.
This product contains a lot more alcohol than the fermentation liquid.
What are biofuels ?
The energy in biofuels originates from sunlight used in photosynthesis. Photosynthesis produces the biomass in plants, and this biomass can be used directly or indirectly as biofuel. Wood can be burnt directly to release energy. Fast-growing trees can be used to fire power stations.
Common biofuels include wood, biogas, and alcohol.
Why are biofuels good? But also bad?
They are better for the environment because the carbon dioxide produced when they burn is balanced by the carbon dioxide they use in photosynthesis while they are growing.
However, land is needed to grow these crops. In some areas forests are cleared for the cash crop and this leads to a loss of plants to absorb carbon dioxide, and an increase in carbon dioxide released by decaying wood. It also causes a loss of habitat.
What are some advantages of using biofuels?
Reduce fossil fuel consumption by providing an alternative fuel.
No overall increase in levels of greenhouse gases, as the plants take in carbon dioxide to grow, and release it when burnt.
Burning biogas and alcohol produces no particulates (smoke).
What are some disadvantages of using biofuels ?
Cause habitat loss because large areas of land are needed to grow the plants.
Habitat loss can lead to extinction of species.
Data shows that some biofuels transfer less energy than other fuel types.
How is biogas made?
Biogas is made by the fermentation of carbohydrates in plant material and sewage by bacteria. This fermentation occurs naturally, for example in marshes, septic tanks, and even inside animals’ guts. Biogas is also produced at some land ll sites, where the gas can be burnt. Sometimes the biogas can explode, making the land fill site unusable for many years.
Why is biogas a good fuel?
Biogas is a mixture of gases that will burn in oxygen, forming a useful fuel:
• methane (50–75%)
• carbon dioxide (25–50%)
• hydrogen, nitrogen, and hydrogen sul de (less than 10%).
Describe small scale production of biogas.
The fermentation happens in a large tank sunk into the ground, which keeps the temperature constant. The family place organic material like dead plants and animal waste in the tank. The bacteria digest this waste, releasing the gas.
Describe the large scale production of biogas.
The gas is generated commercially in large anaerobic tanks. Wet plant waste or animal manure is constantly added, and the gas produced is removed. Gas production is fastest at a temperature of 32–35°C, because the fermenting bacteria grow best at this temperature. The remaining solids need to be removed from the tanks and can be used as a fertiliser in some cases.
What are the uses of biogas?
• as vehicle fuel
• to generate electricity
• for heating systems.
