1. Food Preservation and pH



    To observe the process of fermentation, to compare different types of fermentation.

    Research question

    Fermentation is widespread in nature and plays a leading role in the spoilage of food.


    • A clear plastic bottle 0,75-1l volume.
    • Inflatable rubber ball.
    • Pan or deep bowl, capacity 3-5L; or 5-liter plastic bottle with the cut off top.
    • Bowl or basin, in which you can place the above container
    • Measuring cup (1L).
    • Funnel.
    • Juicy fruit (300 g).
    • Granulated sugar (300 g).
    • Gauze or linen cloth.
    • Digital sensor pH, laboratory pH-meter, pH strips or other indicator of acidity.

    Investigation Protocol

    1. Grind 300 g juicy fruit to a pulp. This can be done, for example, using a blender, or by simply crushing the fruit with your fingers or a spoon. 
      If you choose to experiment with fruit with large seeds (cherry, apricot, plum, etc.), the pits should be removed. Berries (grapes, currants, blueberries, etc.) or apples (apples, pears, etc.) can be crushed without removing the seeds from the fruit.
    2. Measure the pH of the resulting puree. Measurements can be made using a digital pH-sensor, laboratory pH-meter, litmus paper (strips) or other indicators of acidity.
      • If you are using a digital sensor or laboratory pH-meter, then it is desirable to calibrate it (see Project Getting on the Same Page). 
      • Repeat the test three times, each time first washing thoroughly and then wiping the sensor dry. Enter all three measurements in the project Report Form. The program will automatically calculate the average value, summing these three values ​​of acidity and dividing the total by 3. The resulting value will be considered the final acidity. (You will see the results at the time of sending Report Form. They also can be viewed in the “Findings” section after it is sent.)
      • If you use a litmus test measurement of acidity you should follow the manufacturer's instructions. Measurement of litmus test, as in the case of sensors should be repeated three times and all three values ​​to make a profile.
    3. Add 300 g of sugar mashed and 200-300 g of water. Stir the resulting mixture and measure its acidity by the method described in the preceding paragraph of the Protocol.
    4. Leave the resulting puree in an open pan for 1-2 days. Then pour it through a funnel into a plastic bottle of water and put on the neck of the rubber ball.
    5. Take a picture of the bottle of sauce and a scoop of this (early) stage of the experiment.
    6. Place the bottle in a warm place (room temperature 21-25 degrees) for three weeks. At this time the mixture in the bottle may be periodically shaken slightly, but this should be done with care that the mixture not boil over into the rubber balloon. 
      Evidence that the process of alcoholic fermentation will be the inflating of the balloon.
    7. After three weeks, take a picture of the bottle. Then tie a thread around the neck of the balloon. This needs to be done to measure the amount of gas released during the fermentation.

      Carefully remove the balloon tip from the neck of the bottle and measure its volume. 
      The measurement is performed as follows:
      • Pour water up to the brim in the prepared container (a 5-liter plastic bottle with the top cut off);
      • Put a bowl of water in a bowl or basin;
      • Gently and gradually immerse in water inflated balloon so that it completely went under water; with the displaced water will overflow ball in a bowl;
      • Slowly pull the balloon out of the water, and the capacity with the remaining water - from the bowl;
      • Pour the water out of the bowl into the beaker and determine its volume; it will correspond to the volume of gas in the balloon.
    8. Measure the pH of the bottle contents. For this part of the mixture, strain the funnel with a filter (linen or linen cloth) and then determine the pH of the filtered liquid by the method described in Sec. 2 of this Protocol.
    9. Fill in the project Report Form. If you decide to experiment with different fruits, then you must fill in the Report Form for each kind of fruit.
    10. Follow the progress of the project, and participate in the discussion of the results obtained by other contributors.
    Report Form Before filling in the Report Form, please read the Investigation Protocol