Where did the coffee come from? The origin of coffee is explained by isotopes. The origin and history of coffee

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Drinking a cup of mellow coffee to wake up the day is undoubtedly a portrayal of the life of many modern civilized people. You may not know it, but humans have been drinking coffee for more than ten centuries. Due to the age, the origin of coffee has not been examined, and there is a lack of relevant historical evidence.

Coffee has a beautiful story to tell. It is said that more than a thousand years ago, a shepherd in the highlands of southwest Ethiopia noticed that his sheep suddenly jumped with abnormal excitement. It turned out that this abnormal behavior was caused by eating a red fruit by mistake. Therefore, he picked some fruits and went home to boil them. Unexpectedly, the mysterious fruit fragrance was fascinating. Drinking it was even more refreshing. Soon, this mysterious "black drink" began to spread, and after a hundred years, it was introduced into Europe and East Asia, and even became a "black gold" competing for aristocratic status.

Today, coffee is not only a global market of more than 2 billion cups a day, but also an important commercial crop. Gukeng coffee is famous all over the country, but can you be sure that the coffee beans of Gukeng coffee come from Gukeng, which is known as the "hometown of Taiwanese coffee"? Now, let's talk about where coffee comes from and what chemical methods are available to identify coffee's lineage.

Distribution and origin of coffee beans

Coffee beans are mainly Arabica and Robusta. Among them, Arabica has good quality and taste, accounting for more than 2/3 of the total production. In appearance, Arabica coffee beans are small in size (hence the name Arabica coffee), slightly oval in shape, and curved in the center of the fruit; Robstar coffee beans are large and round, and the fruit cracks are straight. Therefore, these two varieties of coffee beans can be distinguished according to these characteristics.

Compared to most other plants, coffee beans are cultivated under harsh environmental conditions. Temperature, altitude and distinct wet and dry rainfall seasons to match the growth and maturity of coffee beans are the most critical factors limiting coffee cultivation. In other words, these conditions limit the growing area of coffee, so that its production area is concentrated in the high altitude area between the Tropic of Cancer, which is commonly known as the "coffee belt".

Although the climatic conditions for coffee cultivation are limited to coffee belts, the soil environment in which coffee grows is not the same. Generally, it can be divided into weathered soils dominated by sedimentary rocks or igneous rocks. Take the countries that mainly produce coffee beans in the world as an example to briefly illustrate the general situation.

In Asia, Papua New Guinea and Sumatra are mainly planted in igneous minerals and volcanic ash weathered soils. Coffee in Taiwan is mainly grown in sedimentary environments, but in a small number of areas such as the eastern part of the country, there are some igneous outcrops, so the coffee growing environment may be affected by igneous rocks to a small extent.

Central and South America is relatively simple, mostly planted in igneous soil environment. Africa is complicated. Arabica coffee is mainly grown in the eastern African plateau, which is dominated by ancient continental crust, but there are many volcanoes in the surrounding areas of the East African Rift Valley. Thus, in the case of Africa, soil properties may vary from region to region. These differences in growing conditions, combined with the climatic conditions described earlier, determine the quality and value of coffee beans in each region.

Because the climate and soil conditions of coffee planting are important factors affecting the chemical composition of coffee beans, they are also important basis for identifying the origin. The greater the variation in these environmental conditions from one coffee bean to another, the simpler the identification process.

Difference in chemical composition

In the early days, scientists relied on differences in chemical composition to identify where crops grew, and thus whether they were grown in the same area. This is based on the fact that crops must absorb nutrients and major and trace elements from the environment when growing, and these chemical compositions vary from place to place. In particular, the concentration of trace elements is relatively low, which is easy to vary due to differences in environmental factors, and can be used as an indicator of "different from place to place". Therefore, as long as chemical elements are analyzed and quantified, and statistical software is used to find out the differences in chemical composition, it is possible to distinguish whether products belonging to the same environment can be distinguished to achieve the purpose of origin identification.

The same applies to the chemical composition of coffee beans. Many studies have shown that coffee beans contain many chemical elements at ppm (parts per million) levels suitable for identifying differences in origin: rubidium, strontium, barium, scandium, cobalt, copper.

But is it really that magical? The author and the research team of the laboratory obtained Arabica coffee beans from more than 21 origins in 14 countries through various channels for research. When these results are statistically analyzed together with the published literature, two important conclusions are unexpectedly obtained. First of all, the composition and distribution of these trace elements do vary from place to place, but the key is that such differences are too small compared to statistical errors.

Again, a blind spot. Metering and differences in chemical composition have the opportunity to tell us whether coffee beans are produced in the same place, but the information revealed is limited to this aspect. Chemical concentration information alone is difficult to pinpoint. This may also be the last straw to crush the camel! The identification of the origin of many foods is gradually becoming less dependent on this method of identification.

Application of Isotope Identification

Compared with chemical element analysis and quantitative techniques, isotope analysis is the trend and mainstream of wide application in recent years.

We need to know what an isotope is. In simple terms, nuclear species of elements with the same number of protons but different numbers of neutrons are called isotopes. Because the number of protons is the same, the isotopes behave very similarly chemically. However, differences in the number of neutrons cause small differences in mass within the nucleus and lead to differences in physical behavior at the microscopic scale. Thus, when elements are exchanged in different "phases," it is easy for these small differences to cause changes in isotope ratios, known as isotopic differentiation effects. For example, common stable isotope systems such as hydrogen and oxygen isotopes (2H/1H, 18O/16O) can change the ratios of 2H/1H and 18O/16O in water vapor during evaporation, rainfall, etc. due to these small differences.

You may feel strange or afraid about the theory of isotope differentiation, but don't worry, because it often takes a long time to explain in college education. Perhaps you just need to grasp a simple concept: the differentiation of stable isotopes provides enough clues about physicochemical interactions for geochemists to do detective work.

isotope clues.

The mechanism by which the ratios of these stable isotopes are differentiated, and the clues provided by the results of differentiation, are the important basis for the use of these isotope tools.

In general, the stable isotopes most commonly used for food origin identification are hydrogen (2H/1H), carbon (13C/12C), nitrogen (15N/14N), oxygen (18O/16O), and sulfur (34S/32S). Hydrogen and oxygen isotopic differentiation is mainly affected by hydrological cycle (such as evaporation, precipitation, etc.), other isotopic systems are mainly related to biological action or ingestion metabolism. Therefore, these isotope systems may not reflect information related to geographical location. That is, not all isotope systems are suitable for crop origin identification.

The strontium isotope system (87Sr/86Sr) is not a stable isotope, but is often used for provenance identification. Strontium isotope ratios are classified as radioisotope systems, but this classification is not due to radioactivity like strontium-90 (90Sr), but rather 87Sr in 87Sr/86Sr decays from rubidium-87 (87Rb). If the mineral contains a large amount of rubidium, it will produce a lot of strontium-87 over a long time (this is the geological time scale discussed here, up to ten million years or even hundreds of millions of years). Therefore, minerals with different Rb/Sr ratios will have specific 87Sr/86Sr ratios, which can be used to distinguish minerals with different lithologies.

As you can imagine, if plants are planted in soil of a particular lithology, the water in the soil reacts with soil minerals, and the plants take the elements they need from the soil water. The 87Sr/86Sr in plants basically reflects the soil environment in which they grow. That's why strontium isotopes are often used to track crops.

In addition, the boron isotope system (11B/10B), which was rarely mentioned in popular science articles in the past, has also emerged in the identification of crop origin. Boron is an essential element in plants such as coffee beans. In cultivated coffee beans, boron comes mainly from fertilizer. Interestingly, boron isotopes in fertilizers used in Central America, Asia and Africa vary regionally. Among them, the ratio of boron isotope 11B/10B in fertilizer in Africa is particularly high, resulting in a high ratio of 11B/10B in coffee beans, which can distinguish coffee beans from other regions in Africa.

Application of Strontium Boron Double Isotopic System

Although there are many isotope systems used to identify crop production areas, after analyzing and counting more than 250 isotope data of coffee beans around the world, it is found that no isotope system can 100% effectively distinguish coffee bean production areas! The main reason is that there are many areas showing similar isotope ratios, which is also the biggest difficulty in certifying the origin of coffee beans (in fact, most crops also encounter the same difficulties and challenges).

However, if several isotope data reflecting different information are looked at together, it will not be so frustrating. Boron isotopes can effectively distinguish African coffee beans from coffee beans from other sources, and strontium isotopes can effectively distinguish coffee beans from Central and South America, which are mainly planted in igneous rocks, and coffee beans from Asian sedimentary rocks and igneous rocks. Therefore, through the analysis of strontium boron double isotope system, coffee origin can be identified more effectively.

Strontium-boron double isotope system has been successfully applied to the origin identification of coffee beans and rice in early years. At present, compared with the monoisotope system, this dual-isotope system method has enabled the resolution of coffee bean origin identification to break through the scale of "continent", and even in several production areas with special isotope ratios, it can be resolved to "country" or smaller scale. In the future, it may be possible to combine other scientific methods to further improve the ability of origin identification.

Strict coffee origin certification has a positive effect on product quality! However, identifying coffee beans from all origins is actually a difficult and difficult task. Chemical identification techniques depend on the diversity of the growing environment of various crops, but are limited by the degree of environmental diversity. However, such restrictions do not hinder the development of science. What's more, who says there can't be cross-domain technical cooperation in the future? Scientists in the past have continuously invested in new technologies and experiments. In the future, they will devote themselves to improving and upgrading technologies, and also ensure that the cup of coffee in hand will continue to be fragrant.