Fermentation. Waste products of pleasent flavour

Wheat_beerHey there folks! I have something to confess.  I find fermenting things like something quite fascinating. And I do so since I brewed my first homemade beer. I’m one of those kind of people that seize almost any situation and try to learn something. And while making beer has an obvious and predictable end (I mean, drinking the beer if everything had gone right) the amount of background behind this quite simple process is overwhelming. I know I’m not the only one interested about this things out there on the internet anyway. I’m looking at you, compulsive brewers 😉

But the fermentation options don’t stop at brewing beer. Yogurt, sour cream and kefir, bread, beer or wine, great part of bakery products, pickles and even some teas. It’s a long list. Fermentation is behind some of the most emblematic foods of a few civilizations. And while the perspective of understanding how these lovely microorganisms pre-digest your food seems disgusting for some people, I found it very intriguing.

So let me jump straight in: What the hell is fermentation?

The basics of fermentation. What is it?

Fermentation is in fact a metabolic pathway. I know it sounds weird, but let me explain. It is pretty obvious that every living body needs energy, which is obtained burning a fuel, usually a carbohydrate. This process is called catabolism, opposed to metabolism. Usually, this fuel is burned by the aerobic respiration at the mitochondria, an energy factory located inside the cell cytoplasm. But when oxygen is not available for this process, there are other ways of obtaining energy: fermentation. The small living microorganism (bacteria) that lives in your yogurt knows very well how to do this.

So what are the key differences between the regular aerobic respiration and the fermentation? The first step stays the same for both: the glycolisis (sugar rupture) breaks up the glucose, our carbohydrate, into pyruvate. This process is developed inside the cytoplasm, and readily after that comes the first difference. In the aerobic respiration process, the pyruvate enters the mithocondria using a carrier, where it undergoes the citric acid cycle, aka Krebs cycle. This results in CO2 and water as waste products. Don’t freak out at this point! This is regular respiration. You inhale O2 and exhale CO2 as waste product while you burn sugar at your muscles. The correlative process can be found in the eucariotic single celled microorganism, like yeast for example.

When oxygen levels are very low, oxygen can no longer be used as final electron acceptor and pyruvate doesn’t enter the mitochondria. Instead, this pyruvate remains in the cytoplasm. There, it is transformed into different waste products. Some of you may be surprised, but the muscles in our body are also capable of fermenting if the oxygen intake is not high enough,  generating lactic acid as waste product, i.e. lactic fermentation. This happens specially when there is a great muscular effort in a short period of time.

Fermentation vs aerobic respiration

Fermentation is not a full energy yielding process, and we can appreciate this by looking at the waste products: No simple molecules at the end? Then there is still energy there to extract. Therefore, if you are a facultative anaerobic little bacterium (which means that you can live both with and without oxygen in your environment) and even if you are fermenting, you should still be interested in “breathing” oxygen too.

Fermentation is a wide field and I could still write more and more about it’s theory and biochemical implications. But I’m no expert, and science is not that funny without experiments, right? So that’s in what I’m working now and what I will speak about in the next post, now that we have a small context. Keep it simple, keep it nice!




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