Evaluating the environmental performance of mezcal production in Michoacán, México: A life cycle assessment approach

Agri-food systems are a critical sector in resource extraction and are essential to boost food security (Bombelli et al. 2019). It is estimated that around 44% of biomass is lost during harvesting, especially in less industrialized chains (El Bilali 2019). Through best practices such as cleaner production, these systems can support more sustainable conditions for all stakeholders (Giannetti et al. 2020). According to the Sustainable Development Goals (SDG) 7 (affordable and non-contaminating energy) and 12 (responsible production and consumption), improving energy efficiency and resource use can help small and medium-sized businesses, particularly those in developing countries, gain access to and integration into value chains and markets (United Nations 2022).

As part of the agri-food systems, the production of distilled agave spirits in Mexico has increased 210% in the last 10 years and represents the second-largest sector of the alcoholic beverage industry (Instituto Nacional de Estadística y Geografía 2022; COMERCAM AC 2022; CRT AC 2022). Tequila and mezcal production in 2021 reached 527 and 8.1 million liters, respectively. Although mezcal represents only 1.5% of production, it increased by 170% in the last year (COMERCAM AC 2022; CRT AC 2022).

Sustainable production and consumption are essential components to avoid the detriment of environmental conditions due to industrial activities (Comisión Económica para América Latina y el Caribe 2018). In the agave distilled spirits industry, tequila manufacturing is industrialized and intensive, whereas mezcal production is mainly artisanal (Tetreault et al. 2021). Cultivation of Agave tequilana has generated soil erosion, chemical pollution, and displacement of traditional food crops and wild agave species (Zizumbo-Villarreal et al. 2013). Mezcal has sustainability challenges to limit uncontrolled growth in agave cultivation (Arellano-Plaza et al. 2022) which could lead to the same environmental problems as the tequila industry.

According to the NOM-070-SCFI-2016 standard, (Dirección General de Normas de la Secretaría de Energía 2016), mezcal is a Mexican alcoholic beverage 100% of agave harvested in established regions and obtained by distillation of fermented juices with spontaneous or cultivated microorganisms extracted from cooked agave heads. Numerous works have been published about the production chain and related procedures of this beverage (Kirchmayr et al. 2014; Rodríguez-Garay et al. 2009).

According to Garcia-Mendoza Abisaí (2022), there are 150 species of agave in Mexico, in populations that are either wild or cultivated. The agave species can be differentiated by their morphological characteristics, such as general plant size, lateral teeth, terminal spines, flowers, and fruit size, among others (Rodríguez-Garay et al. 2009).

The work by Rivera-Lugo et al. (2018) examines four species and five varieties, including three species used for mezcal production. The domesticated and semi-domesticated populations of the agave genotypes used to make spirits are different from their wild counterparts and exhibit a reduced level of diversity (Rivera-Lugo et al. 2018). Extensive monovarietal cultivation of Agave tequilana is threatening the diversity of the germplasm used in traditional agave spirits production in west-central Mexico. Preservation of agave germplasm diversity requires increased cultivation and valuation of local agave species (Vargas-Ponce et al. 2007).

The common functional unit (FU) used is a 750-ml bottle with 40% alcohol volume. Guidelines for a sustainability strategy for the agave and tequila production chains was presented by Mario Molina Center, a non-profit association (Centro Mario Molina and Consejo Regulador del Tequila 2016). Their report includes an LCA of tequila production from Agave tequilana cultivation stage to the recycling of packaging materials, obtaining a total emission of 3 kg \(CO_{2}\) eq/FU. They found that 44% of this value corresponds to direct emissions from production, while the remainder corresponds to raw materials, transportation, and distribution of the product. Madrid-Solórzano et al. (2021) conducted an LCA of an alcoholic beverage called sotol, from gathering and harvesting the Dasylirion species (raw material) to the packaging stage (cradle-to-gate), considering an artisanal bottle. They found that the milling and bottling stages both contribute 78.04% of the total emission value, 5.92 kg \(CO_{2}\) eq/FU. Martínez et al. (2020) outlined an LCA of craft mezcal from Agave cupreata from the nursery of the plant to the final disposal of the packaging materials (cradle-to-gate). They considered a young craft mezcal bottle. They indicated that the energy demand of the craft mezcal resulted in 163.8 MJ/bottle. The stage with the highest contribution to the environmental impacts of mezcal was the manufacturing/processing, contributing 59.6% of them. Previous research studies have been limited by the absence of a comprehensive analysis of materials and energy usage and a failure to address treatment options for major byproducts.

The two major byproducts of the production of plant-based alcoholic beverages, bagasse and vinasse, need to be managed properly. Alternatives have been investigated to propose new applications in which bagasse and vinasse from sugarcane or agave can be used as raw materials for the production of biofuels such as ethanol (Caspeta et al. 2014; Gómez-Guerrero et al. 2019), methane (Valdez-Vazquez et al. 2020), and electricity generation from combustion and gasification (Parascanu et al. 2017). Furthermore, research has been done on composite materials with bagasse, such as reinforcement and filler material for polylactic acid (PLA) green composites (Huerta-Cardoso et al. 2020) and bioactive compounds, membranes, and food packaging (Robles-García et al. 2018). These options have also been investigated through life cycle assessment (Silva et al. 2014; Kiatkittipong et al. 2009; Groot and Borén 2010) proposing an expansion of the waste management system into raw materials in other sectors through industrial symbiosis (Chertow and Ehrenfeld 2012).

Life cycle assessment was carried out on the production of mezcal using a “cradle-to-gate” approach based on the ISO 14044 principles and the ISO 14040 conceptual framework (ISO 14040:2006 2006; ISO 14044:2006 2006), using OpenLCA (Ciroth 2021), the leading free software worldwide. Emissions from the life cycle inventory are provided by literature references and the Ecoinvent database version 3.6 (2019). ReCiPe midpoint (H) was selected as an impact assessment method to translate the inventory data into environmental impact categories. The following categories were selected based on their relevance to the product system: global warming potential (GMP), which helps us comprehend the impact of biomass as a primary energy source in comparison to fossil fuels; freshwater eutrophication (FEP), which addresses the effects of effluent discharge on soil and water bodies in the region; fine particulate matter formation (PMFP), due to the direct exposure of individuals to particulate matter from wood combustion; and cumulative energy demand (CED), which measures the total amount of energy needed.

The material and energy balances were made from in situ measurements. As mentioned below, the study includes the quantification of two agave processing facilities (APF) for operative materials, energy, fossil fuels, and wastes. As far as possible, quantitative information on all essential inputs and outputs connected to the unit process was gathered and/or modeled.

Figure 3 is a flow chart elaborated with STAN 2.6.801, and it displays all input and output flows from the harvest to the refining process.

Based on the material balance, related ecoefficiency indicators can be calculated in a transparent and reproducible way. The following indicators were calculated: the mass yield from harvest, moisture loss, and carbon production during hydrolysis, water usage, the energy efficiency from the ground kiln, distillation, and refining, the rate of waste generation, and the agave material use efficiency.

The mass yield \(y_i\) is the ratio of the process output \(m_{out}\) to the mass \(m_{in}\) of the input, and it describes how much of the original mass remains in the process. The mass yield for agave harvest, agave cooked, and carbon production in the ground kiln is defined as follows:

Fuel-related materials are evaluated according to their energy content in order to determine the energy efficiency of the processes. The energy efficiencies from the ground kiln, distillation, and refining are calculated as follows:

The amount of water evaporated is equal to the loss of mass after the cooking process, where L is the enthalpy of vaporization of the water and \(HHV_{Wood}\) is the higher heating value of the wood. Sensible heating is not considered.

Using the mass balance approach, the waste disposed at the on-site landfill was considered. The core waste intensity indicator (e) is the total waste leaving the system boundary per unit of product delivery. In the case of bagasse and vinasse:

Results for the process indicators for the APFs are shown in Table 2.

For the agave heads, the mass yield in the harvest stage is 41%. Iñiguez-Covarrubias et al. (2001) indicate that, from the total wet weight of an agave, 54% corresponds to the head of the plant, in the case of Agave tequilana. It is important to note that harvest has a small \(m_{loss}\) since some agave heads were contaminated by pests or handled improperly during transportation.

In the ground kiln, wood (\(m_{wood}\)) is used and some charcoal residues (\(m_{charcoal}\)) are produced in such a proportion that they reach around 16.5%, which is an efficiency comparable with the exclusive activities of charcoal production. Weber and Quicker (2018) report that the mass yield for low-efficiency carbon production processes is around 20%.

Energy from wood is used for the hydrolysis of the agave heads, obtaining 22% of moisture removal throughout the process. Considering the ground kiln as a cooking device, it reaches an efficiency of 16.2%. The skills of the people in charge of production are important to make the task more efficient, since sometimes they employ more wood for the process, obtaining fewer efficiencies. Most of the wood fuel is needed for distillation and refinement. The calculated efficiencies of those processes are 6% and 11%, respectively.

It is important to remark that previous indicators quantify the material and energy performance of the production process and do not adequately account for all environmental effects (Huijbregts et al. 2006). It is necessary to translate inputs and outputs into environmental impacts, indicating that LCA evaluations are still necessary.

Figure 4 shows the environmental impact assessment for the mezcal production for both APFs considered in the life cycle inventory (Table 1). Results for each process are expressed as a percentage of the total impact.

Total results corresponding to potential environmental impacts and cumulative energy demand are shown in Table 3 for the two APFs.

The cumulative energy demand (CED) of a product includes the energy consumed during the extraction, manufacturing, and disposal of the raw and auxiliary materials. Most often, agave crops are irrigated using a gravity-flow system during the first year of the cultivation stage; therefore, there is no energy consumption in this stage. Due to the proximity of the agave plantation areas to the APF-1 and APF-2, around 1% of the energy is used for transport during the harvesting process.

The consumption of wood in the hydrolysis, distillation, and refining processes accounts for 87% of the energy used, which shows how crucial biomass energy is to the culture of mezcal manufacturing. The price of wood ranks as the second-highest expense in the process of making mezcal (after the purchase of agave heads). Distributing the usage of forest resources across harvesting cycles can help with forest recovery (Gao et al. 2021), and it can be promoted as a good practice in this industry. The ratio of fossil fuel and biomass energy, on average, is around 5%. The package contribution, on average, is around 8% of the total energy of the mezcal production. Burning bagasse is considered a waste management base scenario; unfortunately, this energy is not harnessed. The total amount of energy per functional unit is 114.7 MJ and 142.2 MJ for APF-1 and APF-2, respectively. In the study carried out by (Martínez et al. 2020), traditional mezcal has a cumulative energy demand per bottle of 163.8 MJ, which is in accordance with the results.

Global climate change is predicted to increase heat, drought, and soil-drying conditions and thereby increase crop sensitivity to water vapor pressure deficits, resulting in productivity losses (Cushman et al. 2015). Climate change may influence the region’s ability to access water and wood, as well as the spread of pests that may compromise the stability of the productive system (Silva et al. 2022; Morales-Barquero et al. 2014; Servín et al. 2014). Carbon emissions are increased when biomass is burned openly for pest control and land clearing during the growing phase of APF-1 (see the process I 2). For the harvest phase, the carbon footprint is due to the transportation of the agave heads from the cultivation area to the APFs. The production of charcoal is responsible for 11% of APF-1 and 21.3% for APF-2 of the \(CO_{2}\) eq emissions during the hydrolysis process. Emissions from the wood burning process in distillation and refining processes consider carbon dioxide as biogenic; with this assumption, therefore, the contributions of burning are mainly due to biogenic methane emissions (Eggleston et al. 2006). \(CO_{2}\) eq emissions are mostly a result of the use of fossil fuels. The packaging process accounts for around 29% of the impact on climate change in both APF-1 and APF-2. Bagasse combustion ends up adding three times fewer impacts than the packing process. The total GWP attributed to mezcal from the current work is 2.1 kg \(CO_2\) eq/FU, which is equivalent to 70% of the impact of tequila compared to the reported results of 3 kg \(CO_2\) eq by Centro Mario Molina and Consejo Regulador del Tequila (2016). The result from Martínez et al. (2020) is 1.7 \(CO_2\) eq, but waste management was not included within the boundaries of the product system.

Eutrophication is a type of water pollution that can seriously harm aquatic ecosystems by overfeeding water bodies with excess nutrients, typically nitrogen or phosphorus. The burning of agricultural wastes contributes to eutrophication, and it is increased mainly by the use of fertilizer (15% for APF-1). Degradation of harvested biomass in the soil makes a limited contribution. The combustion of firewood in hydrolysis and distillation has a negligible contribution, but the ashes were not quantified, i.e., they were outside the limits of the system, and it is important to note that they can also contribute to this category (eutrophication) if their treatment is not adequate. The use of fossil materials generates small contributions to the packaging. Vinasse production in the distillation stage was the key hotspot, causing a significant contribution in the eutrophication category (41.7% for APF-1 and 37.4% for APF-2). Composting is one of the strategies to use the nutrients produced as fertilizer for crops instead of increasing aquatic biomass.

Burning biomass produces particle emissions. This category is essential to understanding the risk to human health by the extended use of wood in this production process to safeguard people. In the cultivation stage, the annual burning of dry biomass affects this category. In the milling and fermentation stages, transportation is where fossil fuel burning arises. This can increase if, in addition, the technology used is old. Hydrolysis is a process without the presence of oxygen, so the amount of smoke is minimal. The largest amount of PMFP emissions occurs in distillation (55% on average for both APFs). Refining and packaging have contributions of 12% and 9% respectively. Bagasse burning has a minor contribution. PM2.5 has been confirmed through fieldwork that this is a major issue since the smoke restricts work activities inside the APFs. In the case of the APFs studied, they are located in an area with a very low-density population.

Wastes contribute between 3 and 58% of the environmental impacts for the described categories for both APFs. There are many proposed alternatives to take advantage of the utility potential of waste, that do not require major changes in the craft manufacturing process.

As shown in Fig. 5, producers responded in the survey which applications for bagasse and agave vinasse seemed most viable for their use in a local context, identifying the use of biomethane for cooking, composting for agave growth, and mixing bagasse with adobe for construction material as the main options. We explore the barriers that must be overcome for these treatment options to be implemented in the mezcal industry.

Although the potential of biogas technologies has been well demonstrated, some barriers in rural areas have been identified, such as high up-front installation costs, no access to financial support or incentives given by the government, and a lack of access to skilled workers for construction, operation, and repairs (Mittal et al. 2018). For cooking applications, obstacles include widely available fuelwood in the local area and low participation of women in decision-making.

Although composting may be utilized as a substrate, the volume of waste produced is greater than the rate of usage locally, requiring the development of a product that can be employed in other agricultural areas.

The generation of alternatives for use, such as adobe and bagasse, requires industrial synergy. Bagasse can be used as a raw material to make adobe, but first, it must be ensured that the conditions are suitable to replace the traditional fiber. Furthermore, the transport and processing of the fiber have additional impacts that limit this type of industry from growing outside the community.

This study provides a comprehensive and transparent evaluation of the environmental impacts of the production of mezcal in Michoacán, Mexico. Eco-indicators of the process were calculated based on a material and energy balance as well as LCA environmental impact categories such as GWP, FEP, PM2.5, and CED. The current results highlight the importance of biomass energy and also reveal the impacts of bagasse and vinasse management scenarios for the craft mezcal system. The sustainable manufacturing of mezcal could only be done in discontinuous batches due to the limited availability of natural resources and the traditional mezcal culture. The main regulations should focus on forest management to make sustainable use of wood (FSC systems), improving road conditions to reduce fuel consumption, and encouraging practices such as avoiding the use of agrochemicals during the growth of the agave, promoting the application of agroforestry systems, and organic pest control that can benefit the maintenance of agave cultivation in the long term. The results of this research can assist producers in prioritizing the reduction of material intensity and environmentally damaging emissions and monitoring progress, or they can serve as the basis for choosing environmentally conscious agave products in purchase decisions. As a future perspective, the identification of hotspots along the production process suggests that efforts can be focused on (a) increasing the efficiency of combustion devices, (b) reducing product losses during distillation, and (c) increasing the percentage of biomass utilized from bagasse and vinasse to make the system more sustainable.