Lab Report: Fermentation of Milk into Kefir

Categories: Chemistry

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Abstract

In this experiment milk was fermented into Kefir, then a series of tests were used to verify that fermentation in fact happened. The tests used to validate the fermentation were a gas production test, pH test, Gram stain, and turbidity test. The results showed throughout the conversion of milk to Kefir there was gas produced, a reduction in pH, more bacteria present, and an increase in absorbency. The outcomes showed that fermentation accompanied 3 positive confirmatory results from the gas production, pH, and turbidity tests, while the Gram stain test functioned as an unfavorable confirmatory test.

Introduction

The main goal of this experiment was to successfully ferment milk into a yogurt-like product called Kefir.

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The fermentation is achieved with a symbiotic combination of various bacteria and yeasts. The main type of germs found in the fermentation of milk to Kefir is Lactobacillus. Lactobacilli ferment the lactose discovered in milk and produces lactic acid, contributing to the sour taste, quality of Kefir.

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The fermented product, Kefir, is not know just for its taste, however more so for the numerous health advantages if can have for the body.

Experimental Procedures

The experiment began by preparing the fermented Kefir product as well as a control sample. Two bottles were filled with milk; Kefir grains were added to the first bottle as the experimental sample, while the second bottle contained only milk and served as the control. Rubber gloves were placed on the tops of both bottles to act as gas collectors, and both bottles were allowed to sit for twenty-four hours.

The following tests were conducted to confirm fermentation:

Gas Production Test: The presence of carbon dioxide gas was examined by checking the gas collectors on the top of each bottle.

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A positive result was observed in the Kefir sample, indicating gas production, while the milk sample showed a negative result.
pH Test: Indicator paper was used to determine the pH of both samples. Two pieces of indicator paper were dipped in each sample, and the color change was recorded. The Kefir sample exhibited an orange color with a pH of 4.5, while the milk sample showed a yellow color with a pH of 7.
Gram Staining: Both samples were subjected to Gram staining to detect the presence of bacteria. Bacteria were observed in both the Kefir and milk samples, though the Kefir sample showed a higher bacterial count.
Turbidity Test: The absorbance of each sample was measured using a spectrophotometer. Five microliters of each sample were diluted with five hundred microliters of water and placed in test tubes for analysis. The Kefir sample exhibited higher absorbance compared to the milk sample.

Results

Gas Production

Samples	Result
Kefir	Positive
Milk	Negative

pH Test

Samples	pH
Kefir	4.5
Milk	7

Gram-Stain

Samples	Results
Kefir	Bacteria present
Milk	Bacteria present

Absorbance

Sample	Result
Kefir	Higher absorbance
Milk	Lower absorbance

Discussion

The gas production test demonstrated that the Kefir sample produced gas, while the milk sample did not. This observation was indicative of fermentation, as carbon dioxide is a direct product of the fermentation process.

The pH test revealed that the Kefir sample was more acidic (pH 4.5) compared to the milk sample, which had a neutral pH of 7. This result confirmed the presence of fermentation, as bacteria produce various acids during the fermentation of carbohydrates in milk.

The turbidity test showed that the Kefir sample exhibited higher absorbance compared to the milk sample, as expected. This increase in absorbance serves as confirmation of fermentation, as the fermented product typically contains more bacteria.

However, the Gram stain test yielded unexpected results. It showed the presence of bacteria in both the Kefir and milk samples. This discrepancy was attributed to the ubiquitous nature of bacteria, as milk may contain bacteria due to various factors. As a result, the Gram stain test served as the negative confirmatory test.

Conclusion

In conclusion, the experiment successfully demonstrated the fermentation of milk into Kefir through positive confirmatory results in three out of four tests: gas production, pH decrease, and increased turbidity. The Gram stain test, initially expected to be negative, showed the presence of bacteria in both samples, which was attributed to the ubiquitous nature of bacteria. Therefore, the experiment confirmed the occurrence of fermentation in the conversion of milk to Kefir, with three positive confirmatory tests.

Recommendations

Future experiments could focus on refining the Gram stain test or using alternative tests to better distinguish between the presence of bacteria in milk and Kefir. Additionally, further investigation into the specific types of bacteria and yeasts involved in the fermentation process could enhance our understanding of Kefir production.