Material Insights · Understanding the Material World

Bioethanol: Techniques

Maize, cane or cellulose: which crop will feed the tank

What this tab covers The methods used to capture this energy: how each works, and how they compare on efficiency, cost, life-cycle emissions, maturity and scale.

Three feedstock routes are covered. Maize (corn) is projected to supply about 61% of world ethanol in 2035 and sugarcane 22% (plus 5% from molasses); cellulose is still marginal. World output was about 32,000 million US gallons (about 121 billion litres, calculated) in 2025.

Comparison

MethodEfficiencyCostLife-cycle emissionsMaturityScale
Sugarcane ethanol246Energy ratio about 9.3 at the factory gateNot quantifiedEU typical and default saving 70% against 94 g CO2eq/MJ, about 28 g CO2eq/MJ (calculated); 20.2 g CO2eq/MJ delivered to New Zealand excluding land-use changemature Brazil produced 8,650 million gallons (27% of world output) in 2025
Corn (maize) and grain ethanol146712Energy ratio 1.5 without co-product credit, 2.1-2.3 with it2025 ethanol price USD 1.50-1.70 per gallon and average net return USD 0.21 per gallon at a representative Iowa dry mill, implying costs net of co-products of about USD 1.3-1.5 per gallon (USD 0.34-0.39 per litre, calculated); corn is about 80% of input costsEU typical saving 55% (default 48%), about 42 g CO2eq/MJ (calculated), natural gas CHP plant, excluding land-use changemature US output 16,494 million gallons (52% of world) in 2025; US capacity 18,330 million gallons a year (September 2025)
Cellulosic (second-generation) ethanol348Energy ratio 5.4 in a switchgrass field studyNot quantifiedEU estimated typical saving 85% (default 83%) for wheat straw ethanol, about 14 g CO2eq/MJ (calculated)early commercial Marginal; not among the main feedstock shares

Sugarcane ethanol has the best energy ratio and among the lowest emissions of crop fuels because bagasse supplies the mill's energy. Corn ethanol needs far more external energy for cooking, distilling and drying, so it saves less carbon, but it dominates output because the US grows vast amounts of corn and mandates blending. Sugar beet sits between them (EU typical saving 67%). Cellulosic ethanol promises the deepest savings from non-food feedstocks, but pre-treatment and enzyme costs have kept it marginal. Land-use change can add substantially to crop ethanol emissions (ICAO adds 8.5-11.9 g CO2eq/MJ for cane and 18.3-34.9 for corn).

How each method works

Sugarcane ethanol

Cane is crushed and the sugar-rich juice is fermented by yeast and distilled. The fibrous residue (bagasse) fuels the mill's boilers, making the process self-sufficient in steam and power.246

Corn (maize) and grain ethanol

Corn is milled and cooked, enzymes turn its starch to glucose, yeast ferments it, and the beer is distilled. The remaining solids are sold as distillers grains for animal feed.146712

Cellulosic (second-generation) ethanol

Straw, grasses or wood are pre-treated with heat, steam or acid, then enzymes break cellulose into sugars for fermentation. Unfermentable lignin is usually burned for process heat.348

Sources

  1. 2015 Energy Balance for the Corn-Ethanol Industry (published February 2016) US Department of Agriculture, 2016
  2. The Sustainability of Brazilian Sugarcane Bioethanol: A Literature Review (Barber, Pellow and de Aragao Pereira, for EECA) AgriLINK NZ / Bioenergy Association of New Zealand, 2008
  3. Net energy of cellulosic ethanol from switchgrass (Schmer, Vogel, Mitchell and Perrin, PNAS 105(2):464-469) University of Nebraska-Lincoln Digital Commons (author record), 2008
  4. Directive (EU) 2018/2001 (Renewable Energy Directive II), Annex V: typical and default greenhouse gas savings for biofuels (Parts A and B); fossil comparator 94 g CO2eq/MJ. Default values not changed by amending Directive (EU) 2023/2413 (RED III); a Commission revision was in draft in 2026 European Union (EUR-Lex), 2018
  5. Annual World Fuel Ethanol Production Renewable Fuels Association, 2026
  6. Monthly Biofuels Capacity and Feedstocks Update, Table 1: U.S. biofuels operable production capacity US Energy Information Administration, 2025
  7. Food crops to remain backbone of global biofuel production through 2035 (summary of OECD-FAO Agricultural Outlook 2026-2035; feedstock shares are 2035 projections) Down To Earth, 2026
  8. Ethanol Production Profits in 2025 (Irwin, farmdoc daily 16:36; representative Iowa dry mill model) University of Illinois, farmdoc daily, 2026