What happens when you ‘ferment’ food and how does it help with preservation?


What happens when you ‘ferment’ food and how does it help with preservation?

In: Chemistry

Anaerobic respiration (respiration without oxygen) happens which produces products such as CO2 and Lactic Acid. Lactic acid lowers the pH of the solution turning it acidic. The acidic environment is unfavorable to many pathogens hence increasing the preservability of a food.

Naturally occurring yeast (which is safe to eat) will consume some of the sugars of the food and produce an acid which is also safe to eat (think vinegar), but will prevent other bacteria from growing.

Change the type of yeast, the growing conditions or the type of food and the yeast will produce mostly alcohol instead.

Certain types of bacteria and yeast can happily live in places that most can’t. They do this by changing the environment (like making it more acid or basic) to a point where other organisms can’t live, but they can. This prevents things from rotting since the organisms that cause the rot can’t survive.

If you can get these organisms onto a food, they can change the environment. They will continue to grow and reproduce until the food gets to the point that even they can’t live there anymore. This has the effect of preserving the food since it may now last for years before actually going bad–few things can now live there and spoil the food.

As an added benefit, the organisms can help bring out nutrients that we can’t get easily from the food through digestion. This can make some foods more nutritious after fermentation.

Good bacteria is usually stronger than bad bacteria. Get yourself some good bacteria to start and it will kill the bad. Fortunately, there’s more good bacteria than bad out there so it normally works out.

Bad bacteria usually has no smell to it. The worry is botulism. Bacillus Botulinum has no smell and doesn’t make CO2 or acids so you can’t see, smell, or taste it. It can also grow aerobic or anaerobic. It prefers anaerobic but, with low oxygen, it will still grow. It’s not the spores that kill you, it’s the toxins.

What we were taught when I was a cook was, “If something should smell bad, and does smell bad, you shouldn’t serve it, but it won’t kill you. If something should smell bad, but doesn’t, it will kill you.” Regardless, it needs to be thrown out. Don’t trust the smell test. If it’s old, it’s old. Throw it, don’t use smell.

Different kinds of microbes (bacteria, yeast, mold, etc) usually don’t like each other (for the most part). They are constantly trying to kill the other unrelated organisms around them so that they can procreate the most. Usually, over time, one of the microorganism families will become the most successful, and dominate the area.

Fermenting food on purpose usually involves attracting/directly applying a type of microbe that is safe to eat, and trying to encourage it to become the winner of the battle. There are different ways to try and encourage a winner, and it depends on what that microbe likes. Common ones are making the environment salty or acidic, removing all the water (drying), and putting it in a sealed container to cut off all the air supply (because some require oxygen to grow).

Then once you’ve got a winner, the winner microbes will start to multiply like crazy and eat the food and produce waste, which further kills the competitors and changes the taste of the food.

Some microbes will produce acid and make the food sour (sourdough bread, vinegar), some will make alcohol (beer and wine), others can produce antibiotics that specifically kill bacteria (blue cheese). All of these things kill the competition but don’t bother the microbes that produce it (at least for a while). Eventually they will either eat all the available food, or they will make the environment so harsh that even they can’t live there any more.

Since you made sure that the winner is a safe microbe, as long as that keeps winning you can eat the food.

Example 1: Your grapes are going to go rotten before you can eat them all. You squeeze them into juice and put the juice in a sealed barrel. This cuts off the oxygen so anything that needs oxygen is gonna lose. You add some yeast to the barrel (giving it a head start). Yeast doesn’t need oxygen, and it eats the sugar in the grape juice and poops alcohol. This kills anything that cannot live in alcohol. This narrows it down a lot. There aren’t a lot of microbes that tolerate alcohol and don’t need oxygen. Your grape juice is now wine and probably safe for a long time now.

Example 2: You make some cheese, but it’s gonna go bad once mold starts growing on it. Most mold isn’t safe to eat, but you have some edible mold. You intentionally get it all over the outside of the cheese wheel. It gets super moldy, but at least you know what kind of mold it is so you can still eat it. You created blue cheese.