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    • Abstract: Production of tequila from agave 225Chapter 15Production of tequila from agave: historical influencesand contemporary processesM. Cedeño Cruz and J. Alvarez-JacobsTequila Herradura, S.A. de C.V. Ex-Hda San Jose del Refugio, Amatitán, Jalisco,

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Production of tequila from agave 225
Chapter 15
Production of tequila from agave: historical influences
and contemporary processes
M. Cedeño Cruz and J. Alvarez-Jacobs
Tequila Herradura, S.A. de C.V. Ex-Hda San Jose del Refugio, Amatitán, Jalisco,
México
Introduction: Agave beverage alcohol white product to which caramel color (generally)
products has been added. Rested tequila (Reposado) and
aged tequila (Añejo) are white tequila matured
Tequila is classically associated with Mexico, in wood containers, preferably oak casks, for at
particularly with Jalisco, a state located in the west least 2 and 12 months, respectively, according
of the country. This beverage is obtained by to present regulations. In practice, the aging
distillation of fermented juice from only the agave period is normally longer and depends on the
plant (Agave tequilana Weber var. Azul ) if 100% characteristics each company wants to give to
agave tequila is required. Fermentation is carried the final product. The products known as 100%
out by inoculated strains of Saccharomyces agave, which are becoming more popular, could
cerevisiae or in some cases by a spontaneous be white, rested or aged and are distilled from
process. Up to 49% (w/v) sugars may come fermented wort with only agave as a source of
from a source other than agave, usually sugar sugars. The labels of these products must indicate
cane or corn syrup, if 100% agave tequila is not that they were obtained using only agave and
required. This tequila could not be labeled as under Mexican government supervision.
100% agave tequila. Tequila is differentiated from the beverage
Different kinds of tequila are produced in 50 known as ‘mezcal’ by the type of agave used in
registered companies in Jalisco. The tequila its elaboration. Mezcal is made from Agave
products made by these companies differ mainly potatorum, which grows in the state of Oaxaca.
in proportions of agave used, production Most mezcal producers use a rudimentary
processes, microorganisms used in the fermentation and distillation process (Sánchez,
fermentation, distillation equipment used and the 1991). There is no technical reason for, or any
maturation and aging times. The product known improvement in the organoleptic characteristics
as ‘silver’ or white tequila must be distilled to a from, the worm inside the bottles of some mezcal
concentration not exceeding 55% alcohol in brands. The worm is primarily a commercial ploy.
volume (v/v) and not less than 38% (v/v) from a Worms are grown in agave plants and introduced
fermented wort containing not less than 51% manually in the bottling line.
sugars from the agave plant. ‘Gold’ tequila is the
226 M. Cedeño Cruz and J. Alvarez-Jacobs
‘Pulque’ is another beverage obtained by water would ferment, producing a very
fermentation of the juice obtained from several appreciated beverage. In fact, this primitive and
species of agave, A. atrovirens and A. salmiana rudimentary method was used for centuries to
among others, by a complex succession of yeast produce beverages from agave, considered a
and bacteria that produce ethanol, a diversity of sacred plant possessing divine properties. In
chemical compounds, and some polymers that other codices, such as Nutall, Laud, Borgia and
give a sticky consistency to the final product Florentine, there are many references to uses
(Rzedowski, 1978; Sánchez Marroquin and of the agave plant for soap manufacture, a
Hope, 1953). Pulque is sometimes mixed with source of fiber, footwear, medicine and sewing
fruits or vegetables, but has poor stability as it is needles as well as thread, paper and rope. In
neither distilled nor pasteurized. fact, Indians could distinguish the different species
Agave plants still serve as food in some states of agave by color, size, stem, leaf width and the
of México; and other fermented regional different uses given each plant (Muria, 1990).
beverages are produced (e.g., ‘Sotol’ in the state The great religious importance of agave was
of Chihuahua and ‘Bacanora’ in the state of apparent in those codices, as only warriors and
Sonora), but only tequila and more recently priests used fermented drinks in ritual cere-
mezcal have reached international recognition. monies.
Another difference between tequila and mezcal In prehispanic México the general name for
and all other regional drinks is that both are all species of agave (or mezcal as it is also known)
subject to an official standard that for tequila is was Metl, which is a representation of the
NOM006-SCFI-1993 (Secofi, 1993), and goddess Mayahuel. The alcoholic drink produced
production is supervised by the Mexican was called Iztac octli (white wine). The first
government. Spaniards to arrive in México referred to the
plant as ‘maguey’, a name used for an identical
plant they had seen in the Caribbean Islands,
Origin and history of tequila where they first encountered new world plants
and animal life (Bottorff, 1971). It was not until
The word ‘tequila’ is believed to originate from arrival of the Spaniards, who brought knowledge
the tribe of ticuilas who long ago inhabited the of distillation techniques, that tequila took its
hillside of a volcano bearing the same name present form (Goncalves, 1956).
located near the city of Tequila. Another possible There are only two main regions for tequila
origin is the Nahuatl word tequitl, which means production in México. The oldest, the Tequila-
work or employment, and the word tlan, which Amatitán region that comprises the Amatitán
means place. Therefore ‘tequila’ would mean village, developed at the end of the seventeenth
place in which labor or work is done. century. The second region, the Jalisco High-
The most ancient information revealing the lands, appeared in the last decade of the 19th
existence of agave and its different uses is from century (Luna, 1991). The first tequila production
the era before the Spaniards in several codices process with a commercial purpose was
preserved to the present time (a codex, from established in the city of Tequila around the end
the Latin codex meaning board or writing tablet, of the 18th century. The main consumers were
is a manuscript volume, especially of a classic in the mining zones located in the state of Jalisco.
work or scripture). The most important is the The Spaniards tried to suppress consump-tion
Tonalmatlnahuatl codex, which notes that certain of tequila in order to reduce competition for
tribes had learned to cook agave plants and used brandy and other wines imported from Spain
them as food and to compensate for the lack of with a decree signed by Carlos III forbidding its
water in desert lands. Also, these tribes sale and production under the pretext that its
discovered that cooked agave when soaked in consumption was the cause of several illnesses.
Production of tequila from agave 227
The results were negative. The governor of the Cultivation and harvest
region later issued a decree imposing a tax on
tequila in order to enrich the royal coffers, thus The blue agave, as it is known, is the only species
permitting its sale in all of New Spain. By the end out of hundreds of Agavaceae with the
of the 19th century, expansion of the tequila appropriate characteristics for tequila production.
industry, helped by the railway, was evident. These include a high inulin concentration, low
However it was not until the first casks were fiber content and the chemical compounds
exported to the US that tequila was known present in the plant that contribute to the final
beyond México’s borders. taste and flavor of tequila to give the beverage
its particular character. Some have attempted to
produce tequila in other states with other agave
The Agave plant species, but without success. The blue agave is
cultivated in the state of Jalisco in the two regions
According to Granados (1985), the genus Agave, with the right climate and soil composition for
which means ‘noble’ in Greek, was defined by its growth, namely the Highlands and the Tequila-
Linneaus in 1753 when he described the plant Amatitán region. The temperature conditions for
A. americana as the first agave species known good agave yields are a minimum of 30C, an
to science. Agave plants, which are often optimum of 260C and maximum of 47°C. Soil
confused with cacti, belong to the family should be fertile but not very deep, 30 to 40 cm.
Agavaceae and are succulent plants with spirally- Good drainage is required to avoid effects of
arranged leaves forming a rosette. Some have flooding, which are very harmful for
definite trunks, but more often they are nearly development of the agave. The plants must be
stemless. The leaves are bluish green in color, planted at 800 to 1700 m above sea level where
over 1 m long in mature plants, and end in a the annual rainfall is about 800 to 900 mm. The
sharpened brown thorn. As Backman (1944) correct planting time is immediately before the
pointed out, the widespread distribution of some rainy season, from June to September, so that
300 species, combined with the fact that the the plants do not suffer from water stress during
plants require approximately 8-12 years to mature the first year of growth.
and hybridize very easily, make the taxonomic Propagation is accomplished by the
and phylogenetic study of the genus Agave vegetative route in agave. Sexual reproduction
extremely complicated and very difficult. The via seeds is not usual. Asexual bulbils develop in
family Agavaceae includes 20 genera and nearly the inflorescence at the base of the flowers,
300 species. Of these, around 200 are found in producing small plants that after some time
México. detach themselves from the floral peduncle and
Several agave species are important from an fall to the soil where they root. Another mode
economic point of view. Fiber derived from A. of asexual propagation is by suckers, which are
foucroydes, grown in the state of Yucatán, is a characteristic type of lateral bud or branch
known worldwide for its use in producing ropes developing at the base of the main stem. Plants
and carpet. More recently, the pulp remaining developing near each mother plant are
after removal of the fiber has found use in animal separated at the age of 3-4 years. These baby
feed. A. salmiana and A. atrovirens are valued plants are called ‘first-class seed’ because they
for pulque production and A. potatorum for are better and healthier (Sánchez, 1991). In
mezcal production. Finally, A. tequilana Weber practice, people use the word ‘seed’ to refer to
var. Azul, named around 1900 by the German such young plants, but from a botanical point of
botanist Weber (Diguet, 1902), is used to view these are rhizome shoots or suckers
produce tequila. (Valenzuela, 1992). Plant cell culture is used
228 M. Cedeño Cruz and J. Alvarez-Jacobs
experimentally by some agave producers, but is the final product when it is diluted or cooled.
not being used commercially due to unavailability One way to avoid this is to treat tequila with
of trained technicians and laboratory facilities to activated charcoal and to filter it through pure
small agave producers. Some developments are cellulose filter pads. This, unfortunately, results
being carried out to improve agave plants, or to in the loss of some aromas.
obtain plants resistant to pests; and these new Agave fertilization is based on soil
plants will be ready in the next two years (CIATE, composition, plant age, and the type of chemical
1993). compound used. The normal procedure is to use
Land for agave cultivation must be cleared urea as a nitrogen source in amounts of 30-70 g
and deep-ploughed, sometimes twice. Agave is per plant added directly into the soil. In some
planted approximately 2-4 m apart in straight lines areas, phosphorus and potassium fertilization is
called ruts. Sowing is done by hand in holes 15 also required. As some agave regions are also
cm in depth. Plant density is around 2000-4000 involved in cattle, swine, and chicken breeding,
plants per hectare, depending on the plantation manure is sometimes employed for fertilization
system used; and yields can be between 30,000 (GEA, 1992).
and 200,000 kg/ha, assuming that the weight of The average maturity time for agave is 10
a harvested plant varies from 15 to 50 kg. This years. Every year following planting, fields are
variation is caused by differences in soil cultivated to loosen the soil and weed and pest
conditions, quality of plants sown, rainfall, pests control is carried out. Each plant matures
and fertilization. Sometimes agave is sown individually. Harvest begins at eight years. The
intercalated with nitrogen-fixing crops such as leaves are cut from the base and left in the field
peanuts, beans, chickpeas or soybeans. After the to recycle nutrients. The harvested plants free
agave has been in the soil for a year, visual of leaves look like large pineapples and weigh
inspection is carried out to replace sick or dead from 20 to 90 kg. They are transported to the
plants with new ones. This operation is called re- distillery. Only the better plants, meaning those
seeding. The percentage of dead plants depends of good size and high inulin content (measured
on soil and plant characteristics, but is generally as reducing sugars) are harvested; but on the
from 8 to 15% (Pérez, 1990). 12th year, all plants remaining (the weakest
Agaves regularly host borer insects that live plants) are cut. These are called ‘drag’ and are
in the stems, leaves and fruits during the larval generally discarded. Agave composition varies
stage. These include butterflies of the family seasonally, but an average would be (wet basis)
Megathymidae and moths of the family Prod- 27% (w/w) reducing sugars, a juice content of
oxidae. Also, the fungi Diplodia theo-bromae and 0.572 ml/g and a pH of 5.2.
Colletotrichum agavae may cause serious
damage to agave leaves (Halffter, 1975; Agri-
cultural Research Service, 1972). Tequila production
Ehrler (1967) discovered that unlike stomata
in most plants, agave stomata close during the Tequilas differ greatly depending on agave quality
day and open by night. This prevents loss of and origin (Highlands or Tequila-Amatitán
water through transpiration during hot daylight regions). The production process also strongly
hours, although it results in a hotter leaf surface influences quality of the final product. Some
than most plants could tolerate. The thick cuticle distilleries still employ rudimentary production
overlying the epidermis, which is quite evident methods, just as they did several decades ago
in tequila agave, apparently prevents damage to (Pla and Tapia, 1990). Most companies, however,
the leaf from high temperature. This waxy cuticle employ technological advances that improve
produces turbidity in tequila because it dissolves process efficiency and consistency; and some
in the distillation step and produces a haze in have implemented a ISO-9000 standard. What-
Production of tequila from agave 229
ever processes are used, tequila manufacture of tequila the law permits the use of other sugars
comprises four main steps: cooking, milling, in amounts of up to 49% by weight in wort
fermentation and distillation. formulation. There are no legal specifications
regarding the type of adjunct sugar sources to
be used in tequila manufacture; and theoretically
Processing harvesting agave any kind of fermentable sugar can be used for
the formulation of wort. In practice and from an
Agave is transported from the fields to the economical point of view, only cane sugar,
factories as soon as possible to avoid weight Piloncillo, cane molasses and acid- or enzyme-
losses, because today most distilleries pay by hydrolyzed corn syrup are employed. Cane
weight and not by inulin content. The heads are sugar is received in 50 kg bags and stored in a
unloaded from the truck in the receiving area of dry, cool place for subsequent utilization.
the factory and must be protected from the sun Piloncillo consists of brown cones of crystallized
and rain in order to avoid withering and fungal complete cane juice, sometimes individually
growth. Although the agave has already been wrapped in corn or cane leaves and packed in
inspected during growth and at harvest, it is sacks. Cane molasses is also used but it is difficult
examined again to reject visually unacceptable to handle and there is risk of spoilage over a
plants or those damaged by pests. At this point, long storage period. Acid- or enzyme-
a representative sample of agave is taken for hydrolyzed corn syrup may be used to formulate
laboratory analysis. Modified AOAC (1990) the wort. All sugars used in wort formulation are
procedures are used to determine reducing routinely analyzed by measuring solids content
sugar content (after acid hydrolysis of inulin) and reducing and fermentable sugar content.
along with pH, moisture, dry weight, juice and
ash content.
Agave heads usually weigh between 20 and The cooking step: hydrolysis of inulin
60 kg, although some can reach 100 kg. They
are cut to sizes that facilitate uniform cooking Cooking the agave serves three purposes. First,
and handling. Different agave cutting systems the low pH (4.5) together with the high
exist, but the use of axes and a specialized tool temperature hydrolyze inulin and other comp-
called ‘coa’ are the most popular. The heads are onents of the plant. The correct composition of
cut in halves or quarters, depending on the these compounds is still unknown. In addition,
weight, and the pieces are arranged manually in cooked agave has a soft consistency that
an oven or autoclave. Band saws can also be facilitates the milling operation.
used to cut the agave heads. Band saws are faster In the pre-Hispanic era, agave cooking was
and less labor-intensive than the manual carried out in holes filled with stones heated
procedure, but the belts break frequently because using wood for fuel. The stones retained the heat
of the resinous consistency of agave. Some for the time needed to cook the agave.
factories tear uncooked agave first with a knife Nowadays some distillers have replaced the
and place the resulting pieces mixed with water stuffed stone holes with brick ovens and heating
into autoclaves to be cooked. is conducted by steam injection after the cut,
raw agave has been introduced into the oven.
Oven cooking is slow, and steam injection lasts
Other raw materials for tequila production around 36-48 hrs to obtain temperatures of 100
0
C. After that period, the steam is shut off and
When producing 100% agave tequila, the only the agave is left in the oven for a further two
source of carbohydrate is the inulin hydrolyzed days to complete the cooking process. During
from agave in the cooking step. For other kinds this step, a sweet liquid called ‘cooking honey’
230 M. Cedeño Cruz and J. Alvarez-Jacobs
is collected and used later as a source of free Extraction of agave juice: milling
sugars, mainly fructose. Also during this step
some of the sugars are caramelized; and some Milling has gone through three historical stages.
of the compounds that contribute significantly In ancient days cooked agave was crushed with
to the aroma and flavor in wort formulation are wood or steel mallets to extract the juice. Later,
due to its high content of fermentable sugars a rudimentary mill consisting of a large circular
(>10% w/v). Finally, the oven door is opened to stone 1.3 m in diameter and 50 cm thick was
allow the cooked agave to cool. The agave is used. Driven by animals, the stone turned in a
then ready for milling. circular pit containing cooked agave and
In most distilleries brick ovens have been extracted the juice. The resulting juice was
replaced by steel autoclaves. Autoclaves have collected by hand in wood basins and carried to
superior efficiency and allow good pressure and fermentation tanks. By the 1950s modern
temperature control, enabling a homogeneous systems were implemented in which cooked
and economic cooking. In a typical autoclave agave was passed through a cutter to be
cooking operation, steam is injected for 1 hr so shredded (except in factories that did this
that the condensed steam washes the agave. This operation before cooking); and with a comb-
condensed liquid is called ‘bitter honey’ and is ination of milling and water extraction, sugars
discarded because it contains waxes from the were extracted. The mills used for agave are
agave cuticle and has a low sugar content (10% by weight) and finally pumped into a fermenter. Although
that is later used to formulate the initial wort. To the amount of sugar employed as an adjunct is
calculate the yield and efficiency of this step, the regulated by law and must be less than 49% by
amount of cooking honey and its reducing sugar weight at the beginning of the fermentation, each
content as well as the cooked agave are factory has its own formulation.
measured. The milling step generates a by-product called
The main difference between autoclaved and bagasse, which represents about 40% of the total
oven-baked agave is that careful control of weight of the milled agave on a wet weight basis.
cooking time, temperature and steam pressure Bagasse composition (dry weight basis) is 43%
must be maintained in autoclaves to prevent cellulose, 19% hemicellulose, 15% lignin, 3%
overcooking or burning the agave. Overcooking total nitrogen, 1% pectin, 10% residual sugars
gives a smoky taste to the tequila, increases the and 9% other compounds. The bagasse, mixed
concentration of furfural in the final product and with clay, is used to make bricks; but it is also the
reduces ethanol yield due to the caramelization subject of research to find alternative uses.
of some of the fermentable agave sugars. This is Examples are use of bagasse as an animal feed
why some factories with both cooking systems or as a substrate on which to grow edible fungi.
reserve the ovens for their better-quality Attempts are also underway to recover its
products. Although it is easier to obtain well- components (cellulose, hemicellulose and
cooked agave in an oven than in an autoclave, pectin) using high-efficiency thermochemical
there is no difference in terms of flavor and reactors (Alonso et al., 1993), to obtain furfurals,
fermentability between agave cooked in make particle board, or enzymes (cellulase and
autoclaves or in ovens if both are correctly pectinase). Many of these projects are at the
controlled.
Production of tequila from agave 231
laboratory stage, and there is not enough populations of 20-50 x 106 cells/ml. The dried
information to evaluate feasibility. yeasts were originally prepared for wine, beer,
In milling, as in all steps of the tequila process, whisky or bread production; and sometimes the
a sugar balance is computed to determine the quality of the tequila obtained using these yeasts
yield. If the yield decreases, the extraction is not satisfactory, with large variations in flavor
pressure in the mill and the water/agave ratio and aroma. To achieve high yields and maintain
are increased to improve efficiency. a constant quality in their tequila, some
companies have been using yeast strains isolated
from a natural fermentation of cooked agave
Fermentation juice. Nutrients are added; along with special
conditions such as a high sugar concentration
Wort formulation or temperature. These isolated and selected
yeast strains have been deposited in national
To produce 100% agave tequila, only agave may microbial culture collections, the most important
be used and the initial sugar concentration ranges being the Biotechnology and Bioengineering
from 4 to 10% w/v, depending on the amount Department Culture Collection of CINVESTAV-
of water added in milling. When other sugars IPN, located In México City.
are employed, they are previously dissolved and
mixed with agave juice to obtain an initial sugar
concentration of 8-16%, depending on sugar Inoculum growth
tolerance of the yeast strain. Wort formulation
in most of the distilleries is based solely on When an inoculum is used, it is grown in the
previous experience. A few distilleries base wort laboratory from a pure culture of a strain of S.
formulation on composition of raw materials and cerevisiae maintained on agar slants in lyophilized
nutritional requirements for yeast growth and form or frozen in liquid nitrogen. All laboratory
fermentation. In these distilleries response propagation is carried out under aseptic
surface methodology is the preferred method conditions using a culture medium with the same
to optimize nutrient concentrations, using ferm- ingredients used in the normal process but
entation efficiencies and the taste of the resulting enriched to promote cellular growth. The
tequila as responses (Montgomery, 1984). To inoculum is scaled-up with continuous aeration
complement nutritional deficiencies of agave to produce enough volume to inoculate
juice and sugars employed in the growth and fermentation tanks at 10% of the final volume.
fermentation steps, urea, ammonium sulfate, Populations of 200-300 x 106 cells/ml are norm-
ammonium phosphate or magnesium sulfate ally achieved. Strict cleanliness is maintained in
could be added. Because the pH of the agave this step as bacterial contamination is highly
juice is around 4.5, there is no need for undesirable. When contamination is detected,
adjustment and the same wort composition is antibiotics or ammonium bifluoride are used as
used for both inoculum growth and fermentation. antimicrobial agents. Once an inoculum is grown,
it is maintained by mixing 10% of the volume of
an active culture with fresh agave juice and
Yeasts nutrients. Although inoculation with commercial
yeast greatly improves yield and turnover time,
Some companies do not inoculate a specific some companies prefer a more complex (in
strain of S. cerevisiae and instead allow natural terms of the microbial diversity) fermentation.
fermentation to proceed. Others inoculate the While yields might be lower and turnover time
wort with fresh packages of baker’s yeast or a higher, the range of microorganism produces
commercial dried yeast to obtain initial more compounds contributing to a more
232 M. Cedeño Cruz and J. Alvarez-Jacobs
flavored tequila. It is also important to recognize to 150,000 liters for the largest ones; and they
that a change in taste and flavor could negatively are constructed of stainless steel in order to resist
affect the market for a particular brand of tequila. the acidity of the wort. Ethanol production can
be detected almost from the onset; and a pH
drop from 4.5 to 3.9 is characteristic of the
Fermentation of agave wort fermentation. The alcohol content at the end of
fermentation lies between 4 and 9% v/v,
Once a wort is formulated with the required depending on the initial sugar concentration.
nutrients and temperature is around 30 oC, it may Alcohol losses may be significant because many
be inoculated with 5 to 10% (volume) of a fermentation tanks are open, allowing
previously grown S. cerevisiae culture with a evaporation of alcohol with carbon dioxide.
population of 100-200 million cells/ml. Some of the largest distilleries have a cooling
Otherwise, microorganisms present in the wort system that keeps fermentation temperature
carry out the fermentation. If an inoculum is not within a tolerable range for yeast, but small
added, the fermentation could last as long as producers do not have these systems. The
seven days. With an inoculum the fermentation fermentation temperature can exceed 40 oC,
time ranges from 20 hrs in the faster process to causing the fermentation to stop with an
three days in the slower one. accompanying loss of ethanol and flavors that
Production of ethyl alcohol by yeast is consequently decreases yields and affects the
associated with formation of many fermentation quality of the tequila. Fermentations carried out
compounds that contribute to the final flavor of with pure agave juice tend to foam, sometimes
the tequila. These are organoleptic compounds requiring the addition of silicones. In worts with
or their precursors produced either in added sugars, foaming is usually not a problem.
subsequent maturation of the wort before it goes Non-aseptic conditions are employed in
to the distillation step, in the distillation process, fermentation, and in consequence bacterial
or in the barrels if tequila is aged. The factors activity may increase. The size of the bacterial
influencing formation of the organoleptic flora depends on a number of factors including
compounds in alcoholic beverages have been the extent to which bacteria grow during yeast
reviewed by many authors (Engan, 1981; Berry, propagation (if used), the abundance of bacteria
1984; McDonald et al., 1984; Ramsay and Berry, on the raw materials and hygiene standards in
1984; Geiger and Piendl, 1976). Experience in the distillery. There is no doubt that the activity
the tequila industry is that the amount of of these bacteria contributes to the organoleptic
organoleptic compounds produced is lower in characteristics of the final product. Occasionally,
fast fermentations than in slow fermentations. As the size of the bacterial population in fermenting
a consequence, the flavor and general quality of wort may become too large (>20 x 106 cells/
tequila obtained from worts fermented slowly is ml), in which case the bacteria use the sugars,
best. The rate of fermentation depends mainly decreasing ethanol yields and sometimes
on the yeast strain used, medium composition excreting undesirable compounds. The same
and operating conditions. The wort sugar content compounds used in the propagation step may
decreases from an initial value of 4-11% to 0.4% be used here to decrease common bacterial
(w/v) reducing sugars if an efficient yeast strain contaminants found in tequila worts. Lactobacillus,
is employed. Otherwise, the residual sugar Streptococcus, Leuconostoc, and Pediococcus
content could be higher, increasing the prod- are the most common contaminants, but Aceto-
uction costs. bacter may be found in fermented worts that are
Fermentation vessels vary considerably in left inactive for a long time prior to distillation.
volume, depending on the distillery. Their In contrast to other distilled beverages, the
capacity ranges from 12,000 liters for small tanks organoleptic characteristics of tequila come from
Production of tequila from agave 233
the raw material (cooked agave) as well as from The most important factor influencing the
the fermentation process. In most of the amount of isoamyl alcohol and isobutanol is the
processes used in the tequila industry, yeast strain. It was found that a native strain
fermentation is spontaneous with the partici- isolated from tequila must produces a higher
pation of microorganisms from the environment, amount of such compounds when compared
mostly yeasts and a few bacteria. This peculiarity with a strain usually employed in bakeries. These
brings about a wide variety of compositions and results agree with those reported for Scotch
organoleptic properties. However, the special whisky (Ramsay and Berry, 1984) and beer
characteristics of the wort make it a selective (García et al., 1994).
medium for the growth of certain kind of yeasts The carbon:nitrogen ratio also has a significant
such as Saccharomyces and to a lesser extent, influence on higher alcohol production. In
acetic and lactic bacteria. In experiments isolating tequila musts, which contain mainly fructose
microbial flora from musts of various origins, (.95%) as a carbon source and an inorganic
different microorganisms were isolated. In most nitrogen source (ammonium sulfate), it was
cases, this difference in flora is responsible for found for both native and bakery yeast strains
the wide variety of organoleptic characteristics that low carbon:nitrogen ratios result in low
of tequila brands (Pinal, 1999). Where a single amounts of isoamyl alcohol: 19 mg/L in bakery
purified strain is used, the final flavor and aroma strains and 30 mg/L for native strains vs 27 and
are more neutral since the bouquet created by 64 mg/L, respectively, for high carbon:nitrogen
the contribution of several stains is richer than ratios. A similar relationship exists for isobutyl
that obtained from only one type of yeast. alcohol production (Figures 1 and 2).
Moreover, when yeast produced for bakery Temperature is a third factor affecting isobutyl
applications is used, the final product is also more and isoamyl alcohol production with higher
neutral. It is also recognized that when non-100% temperatures (e.g. 38 vs 32°C) yielding higher
agave tequila is made, a poorer bouquet is concentrations of those alcohols. On statistical
obtained because since a more defined medium analysis it was found that in addition to the direct
yields a more defined product. effects of yeast strain, carbon:nitrogen ratio and
temperature, the interaction of these three
factors also had an impact on higher alcohol
Organoleptic compounds generated during concentration in tequila (Pinal et al., 1997). These
fermentation results are consistent with the fact that with high
carbon:nitrogen ratios there is a tendency to use
Fusel oil amino acids as a nitrogen source, which implies
the production of fusel oil as a by-product (by
As in many other alcoholic fermentation proc- the Erlich pathway). On the other hand, variables
esses, higher alcohols are the most abundant such as the type of nitrogen source (urea or
compounds produced along with ethanol. We ammonium sulfate) or the amou


Use: 0.1993