215 Agronomy Research 11 (1), 215–220, 2013 Influence of harvesting time on biochemical composition and glucose yield from hemp M. Tutt * , T. Kikas and J. Olt Institute of Technology, Estonian University of Life Sciences, 56 Kreutzwaldi, EE51014, Tartu, Estonia; * Correspondence: marti.tutt@emu.ee Abstract. This article investigates the influence of different harvesting times of hemp samples on their biochemical composition and glucose conversion yield. Samples were harvested from experimental fields of the Estonian University of Life Sciences from July to September in 2011. Dilute sulfuric acid solution was used for pretreatment in combination with enzymatic hydrolysis. Results indicate that the highest glucose conversion rate of 204.1 g kg -1 of dry matter of biomass was achieved by samples harvested on the 18 th of August. The lowest glucose yield of 170.3 g kg -1 was achieved by samples harvested on 25 th of August, which also had a very low hydrolysis efficiency of 46.9%. Biochemical composition and glucose conversion efficiencies of samples vary in time. Samples harvested in September have higher cellulose and lignin content than samples harvested in July. However, glucose conversion efficiencies decrease significantly in later samples. Average hydrolysis efficiency was 51.4%. Key words: glucose, dilute acid pretreatment, cellulose, hemp. INTRODUCTION The increasing industrialisation and motorisation of the world has led to a steep rise in the demand for petroleum-based fuels (Agrawal, 2007). Today fossil fuels take up to 80% of the primary energy consumed in the world, of which 58% is consumed by the transportation sector alone (Escobar et al., 2009). The transportation sector is almost fully dependent on liquid fuels such as petrol and diesel. Continuously increasing oil prices have raised more support for the use of renewable energies. The key advantage of the utilisation of renewable sources for the production of biofuels is the use of natural bio-resources (that are geographically more evenly distributed than fossil fuels) to provide an independent and secure energy supply. Among biofuels, ethanol is one of the most appealing choices, because it can be blended with petrol or used in its pure form in modified engines (Hahn-Hagerdal et al., 2006; Tan et al., 2008). The dominating substrates used for ethanol production today are either pure sugars (sucrose from sugarcane) or easily degradable carbohydrates (starch from cereals or corn). A shift to lignocellulosic plant material is making the utilisation of other crops possible and will enable the production of transportation fuel from herbaceous biomass, corn stalks and straw (Kreuger et al., 2011). Utilising agricultural residual and waste substrates as raw materials for fuel ethanol production will also minimise the potential conflict between food and fuel. Cellulosic ethanol production is a complex process compared to the first generation grain or sugarcane ethanol production. Firstly, it is necessary to break the