The main purpose of this project was to observe the impact of the use of yeast nutrient in the production of pear win. Yeast requires nitrogen, amino acids, vitamins as well as fatty acids in order for it to be able to reproduce. Yeast nutrient, depending on the specific product, can contain a multitude of these different necessary components. Yeast can extract these necessary components from the fruit used to make the wine, however at first it may be difficult. By using yeast nutrient, the yeast is given a guaranteed source of these resources allowing it to reproduce safely.The other goal of our experiment was to observe the impact of a darker bottle during fermentation. Their pear wine fermented in a clear glass bottle while ours fermented in a dark, plastic bottle. Both of our bottles were kept in a dark environment under a cloth. Yeast is a fungus and can be killed by UV light so keeping it dark should in theory, help it reproduce. The final purpose of the experiment was to compare pear, pineapple and cantaloupe wine.
The main observation when comparing our pear wine to their pear wine is that their wine is significantly darker than our more clear wine. The difference between dark and clear wines is their level of purity. Congeners are compounds that are not ethanol that can be found in alcohol as a result of either fermentation or distillation. They are impurities that occur during fermentation and distillation. Darker alcohol has more congeners and is less pure because of it. This means that our wine that lacked yeast nutrient and had a dark plastic container had a different purity to the same wine with yeast nutrient and a glass container. There are two possible interpretations for why our wine had less congeners than the recipe wine. The first is that our plastic container allowed for less impurities than the glass one. The amount of congeners present in alcohol is influenced by the materials and containers used during fermentation and distillation. Glass should allow for less impurities, especially when compared to plastic. Glass is impermeable to oxygen unlike plastic which is permeable to oxygen in some cases. That means that the material of the bottle should not have resulted in our wine being more pure. The more likely source of the purity is the color of the bottle. As mentioned earlier, UV light is harmful towards yeast. Since our bottle was a dark blue instead of a clear glass, it would allow for less light to reach the yeast than a glass bottle. This would explain why our wine was more pure as it was exposed to less light. The second explanation is that the yeast nutrient used in the recipe caused the formation of more congeners. Yeast nutrient allows for yeast to begin the process of fermentation faster by giving it a chance to mature. Since our wine did not use yeast nutrient, it would have started fermenting later than the recipe wine did. Congeners begin appearing during the fermentation process. Their wine spent longer time fermenting so there was more time for congeners to form. This would result in their wine being darker than ours.
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The other purpose of this experiment was to compare the level of alcohol in our pear wine to the pineapple and cantaloupe wine made by our classmates. Overall our wine was by far the most alcoholic out of the three according to all accounts of those who tried all three. It makes sense that pear wine would be the most alcoholic out of the three different wines. Pears are noticeably higher in sugar than both cantaloupes and pineapple. Pears have 9.75g of sugar per 100 grams, cantaloupes have 7.86g of sugar per 100 grams and pineapple has 8.29g of sugar per 100g. The more sugar present during fermentation, the higher the concentration of alcohol in the finished wine. This is because yeast uses sugar to produce alcohol. The more sugar it has, the more alcohol it can produce. Since our wine has the fruit with the most sugar and we added sugar as well, it allowed the yeast to produce significantly more alcohol than our classmates’ wine. It is notable that we did not remove the skin before fermentation which would decrease the alcohol concentration as the skin does not contain sugar. The other comparison to be made between our classmates and our own wine is the sweetness. Sweetness of wine is determined by the amount of residual sugars. Residual sugars are the sugars left in the wine that are not consumed by the yeast in order to produce alcohol. By far our wine was deemed the least sweet out of the three, meaning that our wine had little to no residual sugars remaining after fermentation. This is logical as our wine was also the most alcoholic. There are three explanations for why a wine may have high levels of residual sugar. The first is that the fermentation process was cut short, the second is the addition of sugar after fermentation was completed and third is the addition of specific mixtures to the wine. Since sugar was not added afterwards and specific mixtures were not added beforehand, it can be concluded that the pear wine was closer to finishing fermentation than the other wines.
There are a few conclusions that can be drawn from this experiment. The main conclusion is that the absence of yeast nutrient or the presence of a darker colored bottle during fermentation can lead to a decrease in the amount of congeners present in the finished wine. The other conclusion is that the pear wine was closer to the completion of fermentation than both the cantaloupe and pineapple wine due to its higher alcohol concentration and lower sugar concentration. I hope this project taught you something new about wine and how it is made!