1. KEY CONCEPT Fermentation allows the production of a small amount of ATP without oxygen.

2. If no oxygen is available, cells can obtain energy through the process of anaerobic respiration.
A common anaerobic (without oxygen) process is fermentation.
Fermentation is not an efficient process and results in the formation of far fewer ATP (only 2) molecules than cellular respiration which produces ~36.
There are two primary fermentation processes
Lactic Acid Fermentation (in muscles)
Alcohol Fermentation (yeast and some bacteria)

3. Lactic acid fermentation occurs when oxygen is not available
Lactic acid fermentation occurs when oxygen is not available. Lactic acid is produced during this process. Lactic acid is what makes your muscles sore after vigorous exercise.
For example, in muscle tissues during rapid and vigorous exercise, muscle cells may be depleted of oxygen. They then switch from respiration to fermentation.

4. Alcohol fermentation occurs in yeasts and some bacteria.
Glucose is broken down to produce alcohol, carbon dioxide, and a small amount of ATP.

5. Fermentation is used in food production.
Yogurt - Soy Sauce
Cheese - Vinegar
Bread - Olives/Pickles
Beer/ Meade - Wine/ Ale
Sauerkraut - Malt