The process that occurs in a cell when there is not enough oxygen is called fermentation. Fermentation occurs through the process of Anaerobic Respiration, where instead of using oxygen, organic and inorganic molecules are used as final electron acceptors. The by-product of this process is usually alcohol, ethanol, or acetic acids.
Fermentation is commonly used in lactic acid (in muscles) and alcohol (beers, whiskey) fermentation where the by-product is ethanol. Yeasts are a common organism that uses this process, where it convert sugars into alcohols or acetic acids.