Monitoring th growth of yeast
Yeast is a microscopic fungus, of which there are hundreds of species. It is extremely important brewing ingredient because different strains give different beer types their distinctive and characteristic flavors. When a brewery has found an ideal yeast, it will be retained for many years. However, fresh batches are produced regularly from samples kept under special laboratory conditions to prevent the built up of microbiological contamination. (Just as milk can go sour – yeast and bacteria can also contaminate beer). Individual yeast cells are invisible to the naked eye, and are carried in air current. When they grow on a suitable food source (for example fruit, such as grapes and plums) they form ‘colonies’ of cells. (These can be seen as a fine white powdery film on the skins of the fruit). Yeast can feed on a variety of sugars, converting them into energy in order to grow and multiply. When it first grows, the yeast cells need a supply of oxygen in the same way a animals do when they convert sugar into the carbon dioxide and energy. If animals run out of energy they die. But in the absence of oxygen, yeast obtains its energy from ‘anaerobic fermentation’ in which sugars are converted to alcohol and carbon dioxide. Most importantly for the brewery, yeast produces a variety of flavoring components (through side reactions), which help give the beer its characters flavors. Also use top-fermenting yeast strains that typically ferment between 65-75F and lagers use bottom fermenting yeast stains that typically ferment 50-55F. Pitching temperature should always be 80F or under because yeast will die if exposed to temperature over 110F. Too high of a fermentation temperature or higher alcohols (fusel alcohols). Yeast fermentation time will vary depending on strain, temperature, and fermentations environment, however most fermentations should be complete within 7-14 days.
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Equipment and Materials
3 conical flaks
3 delivery tubes
Ammonium Sulphate (0.5)
Yeast powder (1g)
Sugar (bout 10g)
- Firstly collect all equipment you need.
- Secondly get a conical flask and measure 1g of yeast powder.
- Then measure 0.5 of ammonium Sulphate, pour water into it so it reads 50ml and then put 10g of sugar in. Then mix it all.
- After that u cover it up with cotton wool and make two more.
- When you have all three are made make sure you cover them up with cotton wool.
- Then you put one in a fridge (5 C), the other one in a water bath (15 C) and the last one in a room (50 C).
- And then finally every day keep counting how many bubbles appear in 1 minute for each of the experiments. Keep repeating this process for five minutes every lesson, for a week.
- Do not run around with equipment.
- Do not press hard on the delivery tube as it can snap and hurt you.
- If you drop any solutions in your eyes, wash it out immediately with water.
- Wear goggles while doing the experiment.
- Wash your hands before and after the experiment for safety reasons.
Temp 5 C Fridge
15 C room temperature
Temperature 50 C Waterbath
I think all of my results were good but the room temperature one was better than that rest. Then the fridge temperature one was ok but the waterbath temperature one had dies on Thursday so I dint get full results fro that one. The first problem I had was when my partner made a solution but then left it at the edge of the bench and it fell so we had to make that one again. The other problem was when we were counting the bubbles my partner pressed the delivery tube to hard so is snapped and cut her hand very badly. In the future if I did this experiment again I would make sure I do it right because I no where I made the mistakes, and next time I will not make them mistakes.
Overall I think I did quite well on this experiment because the method was really easy to follow. The only thing that did not go to plan was that the waterbath temperature died. But apart from that the rest was good and I got good results.
It was also quite fun when we had to count the bubbles because all different sizes kept coming out.
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