The burning of fossil fuels for energy is a much larger source of carbon dioxide. Breweries are trying to reduce emissions from fossil fuels by being more energy efficient. Using less energy would reduce Carbon dioxide emissions by using less fossil fuels.
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To make use of the carbon dioxide given off, some is used for carbonating drinks(1).
Controlling Conditions in the Fermenting vessels:
It is crucial that conditions in the fermenting vessels are closely monitored, to ensure that fermentation is happening at the optimum level.
The fermenting vessels need to be maintained at the optimum temperature, as the enzymes that the yeast uses for anaerobic respiration are strongly affected by temperature. The optimum temperature for the yeast to break the sugar down into ethanol is 19oC, and if the temperature were any higher than this, the enzymes within the yeast would stop working as effectively(2). This is because enzymes are globular proteins held in the exact position needed to break down the substrate with hydrogen bonds, and if they are exposed to high temperatures, these hydrogen bonds break. This means that the enzyme’s active site will no longer fit onto the glucose molecules, and the yeast will be unable to respire anaerobically.
Equally, if the temperature was too low, the enzymes would become dormant and fermentation would happen much slower and could eventually come to a halt.
If the enzymes are outside of their optimum pH range, they will begin to denature. This is because changes in pH alter the enzyme’s charge, which alters the ionic bonds holding the enzyme together(3). The enzyme’s three-dimensional shape, specific to an individual substrate would be altered, and the enzyme wouldn’t break down the substrate as effectively(3). The water, or ‘liquor’ as it is referred to in breweries, is distilled to regulate the pH before it is used in brewing. Another step to regulate pH happens in the wort copper, where calcium phosphate is removed, lowering the pH to around 5(2). If the pH were higher than this, it would be outside of the enzymes optimum pH range, causing them to denature.
It is also important to monitor the sugar levels. The sugar store from malted barley provides the sugar that is broken down by the yeast to create ethanol. It is important to have sufficient levels of the substrate (sugar) to ensure substrate is not a limiting factor, limiting the efficiency of fermentation. It is important to ensure that the nitrogen to sugar ratio is not too high in the malted barley, as too much nitrogen could make the beer cloudy(2). Also, too little sugar would make the beer weaker and would lead to a lower ABV (alcohol by volume).
Matthew Condon Candidate 8071 Centre number 26104
Therefore when the breweries analyse the grains for diseases and fungal infections, they also check the sugar and nitrogen content.
The sugar content of the spent grains from the mash tun must also be ascertained, as they are sold as animal feed. If the spent
grains are too high in sugar, they will continue to ferment in the animal’s stomach, producing carbon dioxide. This will cause pressure build up, and the animals stomach could explode.
Another level that needs to be monitored is oxygen, as yeast requires oxygen to carry out essential life processes (other than respiration), and so oxygen must be supplied to the fermenting vessels.
All of these factors must be checked thoroughly, as if fermentation is not happening at its optimum rate, the brewery’s profits would suffer.
To help the brewery run efficiently and productively, breweries re-use yeast for many fermentations. The strain of yeast used by Bateman’s Brewery is ‘Saccharomyces cerevisiae’, which is top fermenting yeast(2). This means that the yeast floats on top of the fermenting vessel as shown:
The yeast floating on top provides protection from the air, and stops gases in the air from causing carbonylation of alcohol into acetic acid (vinegar) (6). It also makes it very easy to collect and re-use the yeast, as it can be removed from the top of the vessel.
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From glucose to ethanol
Before glucose can begin to be broken down, activation energy must be provided. This comes from the breakdown of ATP. The glucose bonds with the phosphate given off from the breakdown of ATP, forming glucose 6-phosphate. The glucose-6-phosphate is then converted into fructose 6-phosphate by an enzyme.
More ATP is then required, to phosphorylate the fructose 6-phosphate into fructose 1,6-biphosphate. This is then split into two 3-carbon sugars called glyceraldehyde-3-phosphate by an enzyme. The glyceraldehyde-3-phosphate is converted into glycerate 3-phosphate.
Then, the glycerate 3-phosphate is oxidised to pyruvate.
Carbon dioxide is removed (decarboxylation) from the pyruvate, forming ethanal. Ethanal is reduced by the addition of hydrogen, and NADH2 is the source of hydrogen used. NADH2 becomes NAD+, and ethanal becomes ethanol. (4)
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Malting
Malting is an important stage in brewing, as it is where the complex molecules such as starch within the grains are broken down so they can be used for fermentation. It is essential that this process happens, as yeast does not produce amylase and has no way of breaking down starch itself. Plants break down the larger storage molecules within the grains, creating smaller, soluble molecules such as glucose that can be transported throughout the plant. The brewer uses this process to access the sugar within the grains that is essential to fermentation.
Malting is done by steeping the grains in water for 2 to 3 days, then draining off the water and incubating them for 10 days between 13 and 17 oC. At Bateman’s Brewery, they use 85% barley grains in malting, but also 5% oats, 5% wheat and 5% rye. Bateman’s Brewery buys in “premium” quality barley, which has a low nitrogen content, and high sugar content. This is because it is more economical to buy fewer grains with higher sugar content than it is to have grains with lower sugar content and have to buy more of them. (1)
During malting the grains are kept in the dark to encourage them to behave as they would do in the soil, and they begin to germinate. They begin to grow shoots and roots, and the grains mobilise starch as sugar.
At the end of 10 days incubation, the waxy coat surrounding the starch has been broken down, and the sugar is released. The grains are put into a kiln and roasted to halt germination. (1)
I have focused on alcoholic fermentation and how conditions in the fermenting vessels are controlled, and how yeast convert glucose into ethanol. I also looked at malting and how the sugar is released for use in fermentation.
Bibliography:
1 - Bateman’s Brewery ‘The Story of Beer’ booklet.
2 – Adam Holmes, assistant brewer at Bateman’s Brewery.
3 -
4 -
5 -
6 -http://en.wikipedia.org/
Word Count - 1485
