As early as 1676, Levin? Hook took the lead in observing the micro-organisms in nature and wrote the first monograph on microorganisms in human history-Levin? Hook discovered the secret of nature. However, both He himself and the western academic circles at that time regarded it as a wonder of nature, and even a kind of evidence that God created life-these tiny creatures seemed to be spontaneously produced by nature. It was not until Pasteur paid attention to the fermentation phenomenon that these magical little creatures gradually changed from an interesting spectacle to a friend of mankind or an enemy that needed to be confronted with it.
A nasty sour taste.
1854, the young pasteur was appointed as the president of Lille Institute of Science in France because of his superhuman intelligence in the study of the optical rotation of tartaric acid crystals. At that time, Lille was growing into an important industrial city, and the brewing industry was an important local industry. During Pasteur's tenure, the wine industry in Lille was often troubled by alcohol quality problems, and wine always had an inappropriate sour taste. 1856165438+1October, a local industrialist, Mr bigo, came to seek pasteur's help, because it was said that his son worshipped pasteur very much.
Fermentation is the key process of brewing, which has long been widely known and widely used. Many of our food production processes are closely related to fermentation, such as steamed bread, bread, yogurt and so on. The history of mankind is full of myths about fermentation, and the fashionable theories of almost every period are used to explain the phenomenon of over-fermentation. For example, the famous Descartes once said, "Fermentation is a mixed and movable force." Don't ask me what this sentence really means. The only thing it can tell us is that physical mechanics was very prominent at that time. The first person who really revealed the basic secret of alcohol fermentation was lavoisier who discovered oxygen. He introduced algebra into chemical research, created chemical equations that everyone is familiar with today, and introduced precision into chemistry, which is of great significance. Lavoisier studied the relationship among alcohol, sugar and oxygen. Finally, he summarized alcohol fermentation as the decomposition of sugar, and gave a beautiful equation. But strangely, although lavoisier had to add yeast to sugar to ferment it to produce alcohol, in his strict quantitative chemical equation, yeast was an unnecessary or incomprehensible monster. He tends to ignore yeast, and with good reason, because in the late stage of fermentation, with the production of alcohol, yeast disappeared.
In any case, yeast is a dark cloud in the study of alcohol fermentation, similar to the dark cloud floating over physics before the revolution of relativity. There are different opinions about revising lavoisier's conclusion. For example, Justus von Liebig, the authoritative German chemist at that time, thought that yeast was very important, or that the disappearance of yeast was very important. He thinks that the decomposition of yeast makes fermentation happen, so he constructs a theory that the decomposed yeast transfers its decomposition state to sugar, which leads to the decomposition of sugar into alcohol. And Swedish chemist Jacob? Bethelius regards yeast as a substance that we call a "catalyst" today, which causes the decomposition of sugar through contact, but he regards yeast as a layer of activated alumina precipitation. The reasonable guess implied in this view was partly developed by later researchers and became the predecessor of modern enzymology.
At that time, there were different opinions on the explanation of fermentation, but no one realized that yeast was a living microorganism, which dominated the final result of fermentation. Therefore, all these theories can't help Mr. Bigo get rid of the sour taste in his wine.
Microscopy and chemistry
Interestingly, tartaric acid, on which Pasteur became famous, is the product of fermentation. His hometown is a famous wine producing area in France, so Pasteur is no stranger to the brewing process of wine, but it only ends there. After all, he never really studied and paid attention to fermentation itself. After accepting Mr. Bigo's request, Pasteur set up a crude laboratory in a basement of the sugar factory. In order to study the relationship between mysterious yeast and fermentation, Pasteur creatively introduced the microscope into his chemistry laboratory. This move is very strange. Even today, the microscope is not an orthodox tool in chemical research.
But it was this move that made Pasteur combine the observation results of microscope with the accurate results of chemical analysis historically, which started the wonderful synthesis of chemistry and biology, and finally created a new field called biochemistry today. In that dark, cold and humid basement, after years of hard observation and chemical analysis, Pasteur caught a glimpse of the mystery of microorganisms, which made him start to think about the relationship between microorganisms and human diseases. In the next few decades, he can no longer live without the wonderful and tiny life displayed under the microscope. His research career is closely related to them, and the fate of mankind has been defeated by microorganisms in ignorance and has undergone earth-shaking changes. Of course, the experiment is hard and full of setbacks. Looking back at the experimental records written by Pasteur, the notebook says: failure, failure, failure. However, with his excellent observation and analysis ability, Pasteur discovered two important phenomena. The shape of yeast changes with the fermentation situation, which is round when fermentation is normal and rod-shaped when fermentation is abnormal. Chemical analysis shows that the more coryneform yeast appears, the higher the lactic acid content in alcohol, and lactic acid is the reason for the inappropriate sour taste of wine. Repeated experiments show that this connection is not a coincidence, which makes Pasteur suspect that fermentation is a life phenomenon, and yeast should be a life, that is, it determines the final fermentation product.
This view was too radical at that time, and he knew it well. If he publishes this article in a hurry, I'm afraid it will only ruin his reputation. There are too many authoritative conclusions and too many controversies in the field of alcohol fermentation. At that time, Pasteur was a rookie, and he didn't want to rush into the center of the whirlpool, so he decided to take the unpopular lactic acid fermentation as a breakthrough, where he might encounter the least opposition. Now, he first needs irrefutable experimental results to prove that yeast is a kind of life.
The secret of yeast
Reproduction is the basic feature of life. If yeast is really a creature, it must and should show this basic feature. However, the observation method at that time was very simple, and the industrial fermentation model was not a suitable experimental model. Yeast usually disappears in the late stage of fermentation, which has long been known and misled lavoisier and Justus von Liebig. It seems that it is necessary to provide a better environment for yeast, but no one has done real microbial culture before. Looking back on the past literature, a report of the Academy of Sciences in 1843 inspired Pasteur, which said that lactic acid inhibited fermentation, but it could be avoided by adding weak alkaline chalk solution.
Pasteur's creativity has been fully exerted here. He transplanted Jacob's gray layer? Betzelius called the precipitates "activated alumina", cultured them in a simplified environment, added chalk to neutralize the expected lactic acid, added sugar to promote fermentation, and then most importantly found a nutrient solution to promote yeast reproduction. This nutrient solution must be clear, easy to observe under microscope, and rich in nutrients to stimulate yeast reproduction. After clever analogical reasoning, Pasteur decided to use beer, which is clear and nutritious, and of course it must be filtered before use. The conditions have been met and the results have been produced. Pasteur finally confirmed that lactic acid fermentation is produced by lactic acid yeast, and its shape and size are different from those commonly used in beer fermentation or alcohol fermentation.
Pasteur collected these important results into a paper on lactic acid fermentation, which was published in August 1857. He mentioned in his paper that he not only successfully identified the yeast needed for lactic acid fermentation, but also cultivated and selected its seeds with suitable nutrient solution, just like cultivating plants. This epoch-making paper is now recognized as the birth symbol of modern microbiology. However, the achievements so far can't really help Mr. Bigo's predicament. After gaining a firm foothold, Pasteur immediately began to "declare war" on the famous and chaotic alcohol fermentation. He identified the essential components for the growth of alcohol yeast and observed various phenomena in the process of alcohol fermentation in detail. At this point, Pasteur put forward an important hypothesis, that is, all the elements needed for fermentation-temperature, sugar, etc. -They are all factors that help yeast to reproduce. The essence of fermentation should belong to biology rather than a simple chemical equation. Pasteur further pointed out that when beer yeast is used for alcohol fermentation, lactic acid and acetic acid will not be produced. The appearance of these products is due to accidental contamination by lactic acid yeast. In this way, Pasteur found the answer to the question asked by Mr. Bigo. The way out of trouble is simple. First kill lactic acid yeast with high temperature, and then transplant beer yeast. 1860, Pasteur was awarded the Experimental Physiology Award by French Academy of Sciences for his outstanding contribution to fermentation research. From then on, Pasteur began to call his research "physiological chemistry" without hesitation, which is the predecessor of biochemistry today.
What do you know about fermentation?
Since then, Pasteur has continued to go deep alone, further expanding his views on lactic acid and alcohol fermentation, covering a wide range of research, including all kinds of annoying or boring or even dangerous corruption and deterioration phenomena. He found that Acetobacter is the key factor to convert alcohol into vinegar, but it is generally believed that nematodes in vinegar vats are an important factor to make vinegar. Therefore, Pasteur designed a simple and convincing demonstration experiment. Just a rope soaked in acetic acid bacteria is needed to let the alcohol flow slowly, and the liquid dripping into the basin becomes vinegar, which can even last for several days. In fact, because Acetobacter grows on the surface of liquid, it will eventually consume the oxygen needed by nematodes, so nematodes in vinegar tanks usually attack Acetobacter. In fact, nematodes that are regarded as essential have nothing to do with vinegar production, but will hinder vinegar production.
186 1 year, while studying the causes of butter deterioration, Pasteur observed Vibrio butyricum, which was the first movable microorganism he encountered in fermentation research. Limited by the basic so-called common sense of animals and plants, Pasteur likes to regard those immobile yeasts as some kind of "plants", so he is very worried that movable Vibrio butyricum may eat the buttery yeast he hopes to find as food just like animals eat plants. After constant observation and patient chemical analysis, he finally found that Vibrio butyricum was the "butter yeast" he was looking for. However, more importantly, he found that Vibrio butyricum was an anaerobic microorganism, and Pasteur's extraordinary observation and analysis ability was fully reflected here. He found that the moving microorganism Vibrio butyricum stopped moving at the edge of the liquid, which was a detail that was easily overlooked. After careful analysis, Pasteur guessed that this was the result of different oxygen concentrations. Assuming that the experiment was carefully designed, Pasteur discovered the first anaerobic microorganism and knew that oxygen was as important to life as water at that time.
This new understanding prompted Pasteur to go back to study the yeast he was already very familiar with. He found that some yeasts obviously have dual viability, namely aerobic and anaerobic survival, and most of the time fermentation is the result of yeast anaerobic survival. Now you understand why you need to isolate the air when making wine or kimchi. The discovery of anaerobic microorganisms opened a new door to nature for Pasteur. He confirmed that corruption is due to the existence of anaerobic Vibrio, and at the same time realized the profound relationship between this special fermentation and the earth's ecological cycle. 1862, he wrote in a letter to the Minister of Education: "After death, life will reappear in another form and with new laws. The eternal law of life on the surface of the earth is that all substances that make up plants and animals will be destroyed and converted into gaseous volatiles and minerals. " So far, in the field of fermentation research, Pasteur deserves to be the first person in the world.
Pasteurized instantaneous sterilization
When Pasteur sang all the way in the field of fermentation and solved the long-debated natural problem, the wine trade in France fell into a trough. To this day, French wine is still famous and irreplaceable. However, in the early days when France and Britain signed a free trade agreement, French famous wines were warmly welcomed by British businessmen at first, but the trade soon collapsed. A British businessman who was almost bankrupt because of selling French wine wrote disappointedly, "… At first, we warmly welcomed French wine, but soon this trade suffered huge losses due to various deterioration problems of wine …". At the critical moment, at the suggestion of the adjutant, Charles Louis Napolé on Bonaparte formally entrusted Pasteur to study the fermentation and deterioration of wine. There is no doubt that he is the best candidate. Don't forget that albo, Pasteur's hometown, is one of the wine producing areas, so Pasteur immediately decided to go back to his hometown and start his research on wine brewing and deterioration. The brewing time of wine is short, and there is only one chance in a year. Pasteur led three students to stay in the laboratory of albo Yi for three consecutive summers from 1863 to study and analyze the brewing technology, preservation methods and deterioration reasons of wine. In order to ensure the quality of the grapes, he even bought a 100 square meter vineyard and hired someone to take care of it. He found that the air, which is usually regarded as the enemy of wine, exactly is the oxygen in it, which is the key factor to make wine stale, that is, more delicious and fragrant. This is a purely chemical process, of course, there should not be too much air, and excessive oxidation will also make the taste of wine worse. However, traditional experience suggests avoiding contact with air as much as possible, and what it really wants to avoid is microorganisms or parasites attached to dust, which Pasteur, who has experienced natural debate, naturally knows very well.
Wine deterioration is a complex problem, and red and white wines have their own common deterioration phenomena. For example, red wine is easy to fade and eventually become bitter when it is old, while white wine is prone to fat deterioration, which makes the wine sticky and greasy. As for the sourness of wine, it is the most common phenomenon in brewing. Pasteur revealed the reasons behind these deterioration phenomena step by step: sour taste is usually caused by the pollution of acetic acid bacteria during fermentation; Fading and then bitterness is caused by a branching parasite similar to fungi; As for the oil change, it is caused by beaded circular fungi. 1866, pasteur published a book "wine research", which brought these research results together.
How to solve the problem of long-term preservation of wine? Pasteur invented the famous heating method-now usually called pasteurization-which is still widely used in many fields. The method is simple. Under the condition of air isolation, wine was heated at 60 ~ 100℃ for a period of time. Pasteur made an accurate experimental demonstration of this, and no one dared to really doubt his experiment, but famous wine manufacturers resisted the heating method, thinking that even if heating could prevent wine from deteriorating, it would definitely destroy its aroma and taste. To this end, Pasteur called for the establishment of a committee to test his heating method. The Committee was established as scheduled, including many celebrities in Paris, including many famous wine manufacturers. In the blind products of wine comparison, it is proved that heating will hardly change the taste of wine as long as it is done according to Pasteur's standards (it has to be admitted that very few people have very strong taste buds). In this regard, the reputation of heating method soon crossed the national border and spread to the New World. An American journalist wrote in new york's Statistical Monthly that "Pasteur's reputation among grape growers is no less than that of the President".
End of movement
Pasteur's research on fermentation finally led him to the door of Ali Cave, where microbial and human diseases occurred, which triggered a fierce revolution in modern medicine and subverted the traditional western medicine inherited from Hippocrates for thousands of years. If Pasteur's first half life is famous for refuting the theory of spontaneous occurrence, then the constant and conservative debate among doctors in his second half life is more realistic for everyone living in the sun today. But Pasteur's unparalleled observation and analysis ability, coupled with excellent experimental design, persuaded everyone who was willing to admit the facts. All this culminated in the development of rabies vaccine. As a viral disease, Pasteur correctly judged that rabies must be caused by microorganisms when there was only a microscope and it was impossible to see rabies virus at that time, and successfully developed a vaccine. (Author: think twice)