Protein is an important part of food, present in cheese, meat, milk, gelatin. Carbohydrate is an energy food, present in bread, flour, starch, sugar. Let's do some fun stuff with these food elements:

Mix 1 ounce of powdered, unflavored gelatin with a cup of garden soil, pour the mixture into a wide-mouthed quart jar, and label it "Protein."

Mix 1 ounce of sugar with one cup of garden soil, pour the mixture into an identical jar, and label it "Carbohydrate."

To a quart bottle of water, add 9 teaspoons of mineral fertilizer, shake the mixture, and allow it to settle. When settled, fill each of the jars with the liquid, cover the jars, and let them stand for two or three weeks.

Keep daily records of observations. You will smell odors and see different colors appear. Some bacteria break down protein food in the absence of oxygen, a process called
putrefaction, while others break down carbohydrates in the absence of oxygen, a process called fermentation.

You might be interested in researching:

(1) the uses people have made of fermentation;

(2) the work of Louis Pasteur (1822-1895), the French chemist who studied fermentation.

I think that putrefaction is the process that occurs when we do our refrigerator projects.