You might be asking what ATP is and why you should care. Besides being the energy source for many cell activities, even those in our own bodies, it is what allows yeast to ferment sugar into alcohol. Without ATP, we wouldn’t have hard cider. I have discussed yeast DNA in previous Mālus Trivium posts and how genes can impact the fermentation process. That got me thinking about how to simply describe the fermentation process and to do that properly, I needed to explain ATP. You can think of ATP as the energy source that allows yeast to process sugar into ethanol and CO2. Once it is used, it becomes ADP, which is recycled later back into ATP. However, the main point is the ATP is an energy source and yeast generally create it through three processes.
- Glycolysis: This is the pathway that converts the sugar glucose (C6H12O6) into pyruvate (CH3COCOO), which is an acid that is a precursor for other compounds. However, this process also creates the ATP needed for fermentation. It is an anaerobic process.
- Krebs/Critic Acid Cycle: This process needs oxygen and is processed through the mitochondria. It creates large amounts of ATP. This is performed in the lag phase of fermentation as the yeast reproduce. It is a series of chemical reactions derived by the oxidation of carbohydrates, fats, and proteins. Nicotinamide adenine dinucleotide (NAD) is another important compound in this process. Also, it is interesting to note that yeast use oxygen in this cycle. Bacteria can also perform this cycle but do not use oxygen.
- Beta-Oxidation: Is a process that breaks down fatty acids into acetyl-CoA, which is an acid used in ester creation as well as an input in the Krebs/citric acid cycle. The creation of acetyl-CoA can also generates a good amount of ATP. It is an oxidative process that also occurs in the mitochondria of the yeast cell.
(1) White, C. And Zainasheff, J., Yeast: the practical guide to beer fermentation, 2010.
(2) Wikipedia, Adenosine Triphosphate, https://en.wikipedia.org/wiki/Adenosine_triphosphate
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