Fermentation of Alcohol and Its Estimation | Biotechnology

In this article we will discuss about the fermentation, recovery and estimation of alcohol.

Alcohol Fermentation:

Principle:

Yeasts ferment molasses and produce alcohol.

Requirements:

1. Molasses.

2. Water.

3. Lactic acid.

4. Yeast.

5. 1 litre flasks.

6. 2/3 NH₂SO₄.

7. Sodium tungstate-10%

8. HC1 (1:10)

Procedure:

1. Dilute molasses with water in order to have a sugar concentration of 10-18%.

2. Adjust pH to 4.8-5.0 using lactic acid since this acid will prevent growth of bac­teria.

3. Inoculate yeast at the rate of 4% into the medium and incubate at room tem­perature for 50 hours in dark after dis­tributing 250 ml of the medium in 1 litre flasks.

4. Estimate initial and residual sugar by Folin Wu method.

Note:

For colorimetric estimation of sugars the broth should be free from proteins. For precipitating proteins in the fermented liq­uor, add equal amounts of 2/3 NH₂S0₄ and 10% sodium tungstate. Yeast cells should be removed by adding HCl (1:10) after centrifugation or filtration. Dilute to 1:100 and use.

Recovery of Alcohol from Fer­mented Liquor:

Principle:

Alcohol can be recovered from the fermented liquor by distilling it.

Requirements:

1. Fermented liquor.

2. Distillation apparatus.

3. Sodium sulphate – 10%.

Procedure:

1. Take a known volume of fermented liq­uor and add 10% sodium sulfate to it.

2. Carry out distillation at 75°-80°C.

3. Collect the alcohol from the receiving flask and measure the amount of distil­late obtained.

4. Calculate the percentage of alcohol. This can be done either by specific gravity method or titrimetric method.

Estimation: Titrimetric Method:

Principle:

Using known quantity of oxidising agent in the system and by measuring the unused oxi­dising agent, alcohol concentration can be determined. K₂Cr₂0₇ is used as the oxidis­ing agent.

Requirements:

1. Fermented broth.

2. Standard solution of alcohol (1.2mg/ml).

(Distill absolute alcohol-Take about 3.5 ml and dilute to 100 ml which will give 1.2 mg/ml).

3. K₂Cr₂O₇ solution-Dissolve 9.0 g of K₂Cr₂O₇ in 550 ml distilled water. To this, slowly add 450 ml of con.H₂S0₄ with con­stant stirring. Store in brown bottle at low temperature.

4. KI solution – 25% aqueous solution.

5. Na₂S₂0₃ 0.1 (N) aqueous solution.

6. Titration equipment.

7. Tubes.

8. Pipettes.

9. Distilled water.

10. Tap water.

Procedure:

1. Distribute 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 and 4.0 ml of the fermented liquor in tubes and make up the volume to 4.0 ml in all tubes from 0.5 to 3.5 ml using dis­tilled water along with blanks and stand­ard solution.

2. Add 10 ml of K₂Cr₂0₇ in all the tubes and incubate for half an hour.

3. Add 100 ml tap water and 4 ml of KI.

4. Titrate against 0.1 (N) Na₂S₂O₃.