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| Fig. 1: The major energy intensive processes involved in the two main phases of wine production. (Source: D. Drescher) |
Wine is a staple product for many people around the world and has been for thousands of years. Its production occurs in two major phases: agricultural, the growth of grapes in a vineyard, and industrial, their transformation to wine in stores though a winery. [1] When measured as a percentage of GDP, industrial wine expenditures account for 0.34% of the world's economy, and 1.3% of the European economy, both appreciable fractions. [2] Vineyards also cover 0.47% of the world's available cropland, and 3.48% of Europe's, making it a major contribution to the agricultural sector which is itself estimated to contribute 14% of greenhouse gas emissions. [1,2] Many studies have separately looked at ways to improve energy efficiency for wine in both the manufacturing and agricultural sectors, but a comparison across the two may be useful to focus energy saving innovation in a particular sector for maximum effectiveness. For this comparison, a useful metric is the amount of energy it takes to make a bottle of wine, and which phase that energy comes from.
As shown in Fig. 1, the major energy draws of the agricultural phase are fertilization, soil tillage, harvesting, and pruning. [1] Fertilization includes the deposition of nitrogen into the soil through liquid spray or solids deposited in the soil, and tillage stirs the soil to incorporate excess plant matter. Both processes are performed by mechanical attachments to diesel-powered tractors. In contrast, harvesting and pruning are conducted by human workers, and involve skillfully removing grapes and excess vine from the plants. Each worker's commute to work is the main energy consumption method for these two processes. All four processes are based on the consumption of liquid fuel, so the amount of fuel bought by the winery and workers can be used to determine energy input. [1] In a case study of an average vineyard in Italy, Marras et al. found that these field practices used on average 14.27 gigajoules (GJ) per year for each hectare of land used to grow grapes. The traveling associated with the vineyard, including employee commutes and grape delivery, used 1.35 GJ hectare-1 y-1, which brings the total energy cost of grape production to 15.62 GJ hectare-1 y-1. The study also found that the vineyard produced approximately 6,500 kg hectare-1 y-1 of grape juice, at a sugar concentration of 22°Bx (22 g of sugar for every 100 g of juice). According to Bayindirli et al., the density of grape juice at 22°Bx is 1.12 g/mL, with which the juice production is converted to 5,803 L hectare-1 y-1. [3] To get vineyard energy usage per wine volume the energy usage is divided by the volume production, giving a value of 2.69 MJ/L.
In the manufacturing phase, when grapes from a vineyard arrive at winery, electric motors operate mechanical destemmers and rollers that remove undesired plant matter, leaving the grape pulp and juice, called the must. This must is then pumped, again using electric motors, to fermentation tanks, where yeast turns the sugar content of the grapes into alcohol. When the wine is ready, solids are removed using electric cooling systems, pumps and motors, and the liquid is bottled and stored using electric filling, corking, and labeling machines. These processes are summarized in Fig. 1. Since machines are used for all the major steps, the energy consumption can be monitored well though analysis of the winery's energy bill. [4] Using this technique, Malvoni et al. found that an average Italian winery produced an average of 7320 kL of wine in a year and used 557,110 kWh in the same period. [4] Dividing these two values and converting to joules (1 kWh = 3.6 MJ) gives 0.27 MJ/L, which is the energy used per volume of wine in the winery processes.
Assuming that winery additives like yeast give negligible volume change, combining the vineyard and winery energy contributions gives an overall energy density of 2.96 MJ/L, which, since a bottle of wine is 0.75 Liters, means that a single bottle of wine takes approximately 2.22 MJ of energy to create. Interestingly, 90% of the energy is due to vineyard processes, meaning the agricultural portion of production uses 9 times more energy than the industrial portion. While this analysis neglects scaling factors that are associated with the operation of different size vineyards and wineries and doesn't account for energy consumption variability between growing regions, it is unlikely that these differences can increase the industrial component by an order of magnitude. This implies that increases in energy efficiency in vineyard practices would have a greater effect on overall wine production price than similar energy efficiency advancements in the winery processes. Therefore, to decrease the energy use of wine production most effectively, interested parties should focus on grape agriculture more than wine manufacturing.
© Dylan Drescher. The author warrants that input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] S. Marras et al., "Carbon Footprint Assessment on a Mature Vineyard," Agric. For. Meteorol. 214-215, 350 (2015).
[2] K. Anderson, V. Pinella, and S. Nelgen, Global Wine Markets, 1860 to 2016 (Saint Philip Street Press, 2020).
[3] L. Bayindirli, "Density and Viscosity of Grape Juice as a Function of Concentration and Temperature," J. Food Process. Preserv. 17, 147 (1993).
[4] M. Malvoni, P. M. Ongedo, and D. Laforgia, "Analysis of Energy Consumption: A Case Study of an Italian Winery," Energy Procedia 126, 227 (2017).