In the eyes of many people, biotechnology is synonymous with serious scientists in white coats doing weird things in sophisticated laboratories. But apparently it is possible to induce biotechnological processes in our own kitchen, without the coat or the expensive equipment.
Biotechnology is defined as the utilization of biological processes for applicative purposes. Some examples for biotechnological processes include development of new strains of plants by genetic engineering, growing living tissues and organs in the laboratory or production of fuel from plants or microorganisms. Nevertheless, there are also much simpler examples for biotechnological processes, such as rising dough for making bread, making beer and even making pickles. In this article we will discuss the processes behind the biotechnology that is taking place in the kitchen.
Respiratory processes and fermentation
Respiratory processes and fermentation in bacteria and yeast underlie all of the processes mentioned above. As with all of us, unicellular organisms such as bacteria or yeast require food in order to survive. When they consume sugar, it undergoes a breakdown process called “glycolysis”, which eventually leads to the formation of pyruvate. The pyruvate has two options: respiration or fermentation. In the first instance, it turns to an oxygen-dependent (aerobic) path, in which it continues to breakdown and change until all oxygen is depleated. This enables the production of large amounts of energy in the mitochondria – the organelle that serves as the cell's power plant. One of the products of this process is carbon dioxide gas, which we will soon come to realize its important role in the kitchen.
The second path, which exists also in the absence of oxygen (anaerobic), is called fermentation. In this path, the pyruvate undergoes processes that break it into alcohol and carbon dioxide (in yeast), or into lactic acid (in bacteria), among other substances.
Respiratory processes and fermentation | By Darekk2 (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
We want our bread dough to be fluffy, so it must undergo a “bubble creating process”. In order for this to happen, we add yeast to the dough, supply them with sugar and water, and let the dough rest. The yeast consumes the sugar, breaks it into pyruvate, as described above, and continues to the oxygen-dependent process in which large amounts of carbon dioxide is produced. The reaction is obvious with the formation of bubbles in the dough. If we leave the dough for too long, the oxygen will run out and the yeast will turn to the fermentation process and produce alcohol and less carbon dioxide (but don’t worry – alcohol evaporates during baking). At this stage, if we put the dough in the oven, it will harden around the bubbles and we will get bread with the desired fluffy texture.
Beer or wine production
Now that we know that yeast is capable of producing alcohol, let us discuss its use in the production of beer or wine. In this process we take grape juice or malt (from barley or other types of cereal) and make wine or beer out of them, respectively. The malt and grapes serve as good resources for sugar, which is consumed by yeast for alcohol production. In this case, we go straight to the oxygen-free path that leads to the creation of carbon dioxide and alcohol. As time goes by, the yeast breaks up more sugar and secretes more carbon dioxide and alcohol, which gradually accumulate, causing their concentration to rise until the beer or wine is ready. In wine production, the process is discontinued halfway for making “semi-dry wine”, or the yeast is allowed to devour most of the sugar, and “dry wine” is produced. This is also the reason for differing in sourness.
Another interesting fact is that beer and sparkling wine contain small bubbles of carbon dioxide, while regular wine does not. The reason for this is simple – the carbon dioxide is usually removed from the wine. In addition, it is interesting to note that the carbon dioxide bubbles in beer or sparkling wine are much smaller than those found in soda. This is due to particles in the wine and beer that adhere to the bubbles. While soda is a lucid beverage without any particles, so the carbon dioxide bubbles adhere to each other and become larger.
Until now, we have dealt with yeast fermentation. Now it is time to move on to bacteria. As previously mentioned, bacteria also undergo a fermentation process, but instead of producing alcohol, they produce lactic acid – the same substance that gives rise to the sour sensation we feel in our mouth after eating something sweet. Adding acid to milk causes the milk protein casein to change and form lumps of protein and fat, which are actually the substance that comprises cheese. This process is called curding.
In order to demonstrate the curding effect, we can perform an experiment in which we add milk to a bottle of coke. After a few hours, we will be able to detect sunken cheese lumps due to the phosphoric acid present in the coke.
Please note! The same effect can be achieved by adding milk to lemon juice, vinegar or any other acid, and it is a result of a reaction between the proteins in the milk and the acids in the coke. It is just simple chemistry.
Therefore, during the process of cheese production, certain bacteria are involved, which secrete lactic acid and cause the curding process. Afterwards, the water is filtered out, leaving only the lumps of protein and fat that comprise the cheese. The more water extracted (by filtration or salting), the harder the cheese will be.
And now we have reached the topic of pickled cucumbers, and all their other pickled friends. In this case, as with cheese, we want to let the bacteria do the job. For this purpose, we place cucumbers in a container with water and salt or vinegar, which prevent the growth of unwanted strains of bacteria. In this case what happens is a decomposition process of the cucumber, caused by those same lactic-acid-producing bacteria. When the amount of lactic acid crosses a certain threshold, even these bacteria cannot withstand the conditions and die, and we are left with a jar of pickles.
As we saw before, when we make beer or wine, a fermentation process takes place, during which alcohol is produced. However, as anyone who has opened a bottle of wine and left it outside knows, after a while, the wine goes sour. The reason for this is that bacteria break down the alcohol into acetic acid – the substance that gives the vinegar its taste. This process can only occur in the presence of air, and this is why it is so important to avoid any contact with air while making wine or beer.
Special thanks to Dr. Michal Stolarsky Ben-Nun for her assistance on preparation of this article.
Dr. Erez Garty
Davidson Institute of Science Education
Weizmann Institute of Science
Article translated from Hebrew by Elee Shimshoni, PhD student at the Weizmann Institute of Science.
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