Agave
(From https://www.britannica.com/plant/Agave)
agave, (genus Agave), genus of the some 200 species of the family Asparagaceae (formerly Agavaceae), native to arid and semiarid regions of the Americas, particularly Mexico, and the Caribbean. The genus contains a number of economically important species, especially those required for the production of mescal liquors, including the blue agave (Agave tequilana) used for tequila. Sisal (A. sisalana), henequen (A. fourcroydes), and cantala (A. cantala) are significant sources of fibre and are of interest as potential bioenergy crops. The century plant, or maguey (A. americana), and blue agave are the primary sources of agave nectar, a syrupy sweetener. Additionally, a number of species are grown as ornamentals in desert landscaping.
Agave plants have a long history of ethnobotanical importance, especially to the peoples of Mexico, where the genus is most diverse. Many species have strong fibrous tissue in their leaves, which makes them useful for ropes, brushes, sandals, nets, sleeping mats, and other similar items. The fibres of some species can be removed with the terminal spine of the leaf still attached, forming a type of needle and thread. In many species, the leaves of the rosette can be removed to reveal the thick stem, or heart
, which can be roasted and eaten directly or ground into edible patties. The stem is particularly dense in carbohydrates immediately before flowering, and it is also the source of mescal alcohols and agave nectar. To prepare mescal, the sap of roasted or pressure-cooked agave hearts is fermented and distilled; different species are used for different types of mescal, with blue agave being the only species used for tequila. Similarly, agave nectar, a syrupy sweetener used as a sugar alternative, is not true floral nectar and is made by extracting, filtering, and heating the sap of the hearts of several species, notably blue agave and the century plant. Pulque, another traditional Mexican alcohol, is made by fermenting the sap of the inflorescence stalk. The raw sap of most Agave species is considered toxic and requires cooking prior to ingestion.
Description
Agaves are characterized by a rosette of succulent or leathery leaves that range in size from a few centimetres to more than 2.5 metres (8 feet) in length, depending on the species. Most bear spines along the edges and the tip of the leaf, for which they are occasionally confused with unrelated cacti. The leaves range in colour from pale green to blue-grey and can be variegated or striped. Many species are able to reproduce vegetatively and generate clonal rosettes at the base of the main stem or nearby via underground rhizomes; some species produce bulbils (bulblike structures that can form new plants) on the inflorescence. The plants are generally monocarpic—meaning that each rosette dies after flowering and fruiting—and most do not live longer than 30 years. The yellow, pale green, or red flowers are borne in tall branching or unbranching inflorescences that can reach more than 9 metres (30 feet) in height in some species. Each flower consists of six petals and an inferior ovary (i.e., the other flower parts are attached above the ovary) and produces copious amounts of nectar. The flowers are pollinated by bats, insects such as bees and hawk moths, or birds, depending on the species. The flowers produce capsule fruits.
Adaptations
(by J. Ryan Stewart
(From https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2015.00684/full)
Over the past several million years, agaves evolved physiological mechanisms and anatomical traits, which enable them to be productive despite growing in harsh semi-arid environments, where water and nutrients are severely limited. The CAM pathway enables agaves to colonize semi-arid environments where water is scarce and soil surface temperatures often exceed 55°C. Moreover, the succulent and fiber-rich nature of agave leaves allows for the continuation of CO2 fixation and other vital biochemical reactions during extended periods of drought, which can last up to 7 years or more. In addition, the rosette arrangement of agave leaves allows for maximal absorption of photosynthetically active radiation, and allows for the funneling of water to their relatively shallow root systems. The roots of agaves can shrink in response to drying soils, minimizing water loss, but they can also quickly generate fine roots to permit rapid water uptake after a short-lived rain event. Moreover, dead leaves accumulate at the base of agaves, buffering living leaf tissue from high soil surface temperatures, which can range from 50 to 55°C. Dead agave leaves also likely contribute to reduced soil evaporation and increased soil organic matter.
Agaves have several other traits that have made them suitable as crops over several millennia. These include their starch-rich stems (caudices), semelparous flowering, long-lived perennial habit, natural proclivity to grow on rocky, infertile soils, fiber-rich leaves, and ease of vegetative propagation.
Agave as Food
The slow growth of agaves plus their monocarpic flowering and vegetative reproduction pose some challenges to not only establishing and harvesting them with conventional agricultural implements, but also to improving them through classical and molecular plant breeding. And although some agaves have been reported to have impressive yields, only a fraction of the yield harvested can be consumed and digested. Leach (2007) estimated that only 24 people would have their annual caloric requirements met from an annual harvest of nearly 10,000 agave plants, which is largely due to the high levels of non-digestible carbohydrates in the form of inulin-type fructans. Inulin-type fructans is the major carbohydrate found in agaves. However, if eaten in a mixed, balanced diet, agaves could act as an alternative fiber source. They could also be used as prebiotics. Enzymes in digestive tracts cannot hydrolyze beta-glucosidic bonds in inulin-fructans, which consequently promotes the growth of beneficial microorganisms in mammalian intestines. Such microbial growth can lead to numerous health benefits, including reduced gut infections, improved lipid metabolism, higher mineral absorption, and reduced risk of cancer. Based on prehistoric diet analyses, Leach and Sobolik (2010) surmised that modern-day diets could adapt to higher levels of inulin-type fructans. Such compounds have been found to be effective in weight control in laboratory animals.
The exploration of other end products of Agave is also warranted, including incorporation into dairy, bread, and candy products. If pursued as a food crop, selections could be made for agave clones with higher levels of digestible carbohydrates. On the other hand, the high levels of inulin-fructans could possibly lead to delayed digestion in the intestinal tract, which could be beneficial for diabetics. Regardless, sensory analysis will be required to determine consumer acceptability of agave. While the likelihood of agave being widely eaten in the U.S. or other developed nations is low, opportunities exist for it to become a part of regional niche food markets.
Agave as Beverage
Besides being used as a food crop, some agaves were also widely harvested in the wild and cultivated to produce non-alcoholic and alcoholic beverages. In pre-Columbian Mexico, native peoples in the region would cut or remove the nascent inflorescence from reproductively mature agaves to allow the sugar-rich sap from the head to accumulate in the hollowed-out circular center. Agaves commonly used for beverages are collectively known in Spanish as maguey pulquero, and include Agave americana, Agave angustifolia, Agave atrovirens, Agave ferox, Agave mapisaga, Agave salmiana, and other species of local importance. The sap, which was intended for fueling development of the emerging inflorescence, is called aguamiel. Aguamiel is crystalline and high in sugar content (12°Brix), with an average pH of 7.5. Although diminished nowadays in cultural importance, aguamiel is still harvested in central Mexico with methods used prior to Spanish colonization. Aguamiel is collected at least every 12 h after scraping the hollowed area in the head. Production lasts, on average, from 4 to 6 months. According to Nobel (2010), a single agave plant can produce 700 L of aguamiel. In recent years, there have been efforts to promote its use as an alternative traditional beverage due to its purported nutritive benefits, including fructo-oligosaccharides, which have prebiotic properties, and several essential amino acids, vitamins, and minerals.
Pulque
Perhaps more culturally significant than aguamiel to indigenous groups in central Mexico was its fermented product, pulque. Pulque is a milky fermented liquid, largely made from A. salmiana, A. mapisaga, and A. americana sap, which has an herbal aroma, low alcohol content (4–6%), and high acidity (pH = 3.5–4.2). The drink, whose origins date back to the Early Classic period (AD 150–650), was used in religious rituals to honor the Aztec goddess, Mayahuel, and was regularly consumed by Aztec nobility. Possibly more importantly, however, the beverage provided a source of calories and nutrients during times of shortfall in corn and bean production. The beverage is still consumed during festivals and significant cultural events, and is considered an important component of maternal diets in the highlands of central Mexico, due to it being rich in micronutrients. As with aguamiel, pulque is still produced using the same methods developed hundreds of years ago. After collection, aguamiel is placed in wood barrels or goatskin bags, and then transferred to larger barrels to allow for fermentation. Fermentation starts within the plant due to naturally occurring microorganisms, including yeasts, lactic-acid bacteria, ethanol-producing bacteria, and exopolysaccharide-producing bacteria, but is accelerated by the addition of previously produced pulque. The entire fermentation process, which is done primarily by regional artisans under non-aseptic conditions, ranges from 12 to 48 h.
Upon fermentation, pulque is stored without preservatives in wood barrels, and is distributed daily for sale. Consumption of pulque must occur within a few days after fermentation because it otherwise quickly undergoes decomposition and acquires a putrid stench. Up to the first half of the twentieth century, pulque production was a profitable industry, but due to various factors, its economic importance has diminished. However, there are currently nearly 20,000 hectares in Mexico devoted to aguamiel and pulque production, with about 200 million L produced annually. Some companies have industrialized the process, which could lead to increased production. However, due to inadequate hygiene conditions and the risk of contamination by pathogenic bacteria, concern exists regarding the safety related to the fermentation process of pulque production. Gómez-Aldapa et al. (2011) found that there was low risk of consumer exposure to common pathogenic bacteria, such as Salmonella, Staphylococcus aureus, Listeria monocytogenes, Shigella flexneri, and Shigella sonnei, when pulque was processed following conventional methods. This was possibly due to the low pH of pulque and the presence of ethanol and saponins. However, Escherichia coli O157:H7, a virulent foodborne pathogen, was found to survive fermentation cycles in pulque production. Before widespread production occurs, improvements in proper handling and hygiene of those producing pulque are needed to reduce consumer health risk.
Tequila
(From https://www.britannica.com/topic/tequila-distilled-liquor)
tequila, distilled liquor, usually clear in colour and unaged, that is made from the fermented juice of the Mexican agave plant, specifically several varieties of Agave tequilana Weber. Tequila contains 40–50 percent alcohol (80–100 U.S. proof). The beverage, which was developed soon after the Spaniards introduced distillation to Mexico, is named for the town of Tequila in the Mexican state of Jalisco where it is produced.
Upon maturity the pineapple-like base of the agave plant fills with sweet sap, or agua miel (honey water
). The bases are steamed to aid in extracting the sap; this juice is fermented and then distilled twice to achieve the desired purity. Some brands are aged in oak vats, which allows the distillate to mellow and take on a pale straw colour.
Tequila is mixed with lime juice and an orange-flavoured liqueur to make the Margarita cocktail, which is served in a glass rimmed with salt. Mexicans usually prefer tequila unmixed, accompanied by salt and a wedge of lime. The drinker takes salt, tequila, and lime in rapid succession, thus combining all the flavours.