Researchers Evaluate Agave’s Potential for Ethanol

High-yielding varieties promise agave-based ethanol could surpass even sugarcane yields
By Remigio Madrigal-Lugo and Alejandro Velázquez-Loera | February 22, 2012

Ethanol currently comprises 85 percent of global biofuel production, with nearly 90 percent of ethanol production coming from just two producers, the U.S. and Brazil. Ethanol yield per hectare varies widely, due to differences in crop yield by country, as well as the efficiency of conversion. Brazil has the highest ethanol yield per hectare of 5,476 liters (585 gallons per acre), from an average yield of sugar cane of 73.5 tons per hectare and a conversion efficiency of 74.4 liters of ethanol per ton of feedstock. In the U.S., average corn yields of 9.4 tons per hectare and 399 liters-per-ton conversion efficiency produces 3,751 liters of ethanol per hectare, according to one 2007 estimate.

Up to now, there has been no reported use of agave feedstock for ethanol production. In Mexico, most industries producing alcoholic beverages from agaves, such as tequila or mezcal, have seen successful production levels. In late 2007, the tequila industry reached a historic production of 292.1 million liters, of which 149.7 million was exported to more than 100 countries. The mezcal industry also achieved a record 500,000 liters. Other products manufactured from agaves include pulque and bacanora (beverages), inulin (a plant fiber used as a food additive) and fructose syrup.

Agave used for tequila and mezcal is cultivated on a large scale in Mexico while other types are planted in smaller plots or on edges of fields. Agave plants are found in all kind of soils, from shallow and eroded with steep slopes to flatter lands with better fertility conditions. In the State of Jalisco, where most agaves are grown, the Tequila region has a 200-year tradition of cultivating blue agave. In this area, the altitude ranges from 800 to 1,360 meters (2,500 to 4,400 feet), the average annual rainfall is 1,340 millimeters (53 inches), the average temperature ranges between 22 and 26 degrees Celsius (71 to 79 degrees Fahrenheit). In the Los Altos region, another area of great importance for agave cultivation in Jalisco, the altitude ranges between 1,600 and 2,020 meters, and the climate is mild. The average annual rainfall varies from 1,420 to 1,500 mm, the average temperature ranges between 18 to 26 C.

Plant populations can vary from 800 to 5,000 plants per hectare, although an average of 3,000 agaves per hectare are planted in commercial plantations. Sometimes seasonal crops such as corn and beans are sown between agave rows. Comprehensive control of pests, diseases and weeds is required and fertilizer is applied as needed. Mature plants can be harvested at 6 to 12 years. Expert workers, called jimadores, use a long-handled blade to hand harvest the plants, cutting the stems first, then trimming the leaves to be left on the field while the stems are taken to the factory for processing.  

Statistical data on average yields per hectare for agave is not available, but in several meetings with agave producers, most agree that small producers and small industrialists producing their own raw material harvest agave heads that average 25 to 30 kilograms with 17 to 21 percent sugar content and harvest cycles of eight to 10 years, utilizing few agronomical practices. On the other hand, large tequila producers who raise most of their own raw material, harvest agave heads that average 40 to 55 kg with 24 to 27 percent sugar content and cycles of six to eight years to harvest time. These producers apply appropriate crop practices on their plantations.

In visits with agave producers, we have admired pictures where technicians pose beside huge agave heads. Despite efforts by many, these magnificent plants with exceptional characteristics for high yields have not been reproduced by the traditional method of suckers. Instead, new methods are in development to develop high-yielding agave varieties from mother plants with characteristics of high weight of the stem or head, sugar content, age to maturation and architecture of the plant (which affects the yield).   The establishment of highly productive plantations from these new varieties promises to supply traditional agave markets as well as introduce agave as a competitive ethanol feedstock.

As researchers in the Plant Science Department at Chapingo Autonomus University, we first worked on applying biotechnology techniques on the agaves starting in 1979. We developed an in vitro propagation protocol for henequen (Agave fourcroydes Lem.) and initiated an in vitro germplasm bank. The first plantation with agaves reproduced in the laboratory was established in the State of Yucatan. In 1981, we continued the investigations with the agave for tequila (Agave tequilana W. blue agave) and the agave for mezcal (Agave angustifolia Haw.) and developed the specific protocols for their in vitro propagation. In 1989, we planted the first blue agave and agave for mezcal plots in the State of Jalisco, and six years later we harvested the stems and produced the respective alcoholic beverages.                 

After years of research work and the observation of millions of plants, we have selected those agaves whose stems weigh from 140 to  213 kg, with 17 to 38 percent sugar content and a six-year harvest cycle.

With the methodology developed for the agave germplasm bank, we have continuously kept plants under in vitro conditions for 30 years. The characteristics of these agaves when they have been grown in the field are equivalent to the original mother plants. Thus, it is possible to conserve agaves of these species with diverse outstanding characteristics in the germplasm bank for long periods of time.

Another result of the applied methodology is the development of a variety of agave for mezcal that we are about to register in Mexico. The main characteristics of this agave variety are stems of 150 kg with 27 percent sugar content and six years to harvest time.  The plant characteristics are presented in the comparison of ethanol production from corn, sugarcane and agave found in the table.

An agave variety with stems of 150 kg and 27 percent sugar content, grown at a density of 3,000 plants per hectare and harvested in six years has a potential annual ethanol yield of 7,500 liters per hectare. This yield is highly superior to those reported for corn and sugarcane. Higher yielding varieties of agave still can be developed from elite plants seldom found in the plantations. Second-generation ethanol production from cellulose contained in leaves and the waste pulp of the agave stem will considerably increase the yield.

Though yields from agaves raised by tequila and mezcal producers are not presently competitive with sugarcane and corn, we propose these high-yielding varieties in development could allow us to take advantage of this feedstock to produce tequila or mezcal and become a viable and competitive option for ethanol production.

       
Authors:  Remigio Madrigal-Lugo
Alejandro Velázquez-Loera
Researchers, Plant Science Department
Chapingo Autonomus University
01 (595) 95 21500 ext 6215
remigiomadrigal@hotmail.com
alevelo4207@hotmail.com