Breeders at IBERS have been developing varieties of perennial rye-grass (PRG) (Lolium perenne) with increasingly higher levels of water soluble carbohydrate (WSC) and higher digestibility as a way of improving protein utilization by ruminants. The proportion of WSC in these varieties usually exceeds 30% and can be as high as 40% on a dry weight basis. While the very low lignin content (<5%) means the fibre fraction contains proportionately higher levels of potentially fermentable sugars (up to 90% fibre DM). A WSC rich juice (9-18% w/v) can be extracted from fresh grass using a screw press and fermented to ethanol with the addition of yeast and a novel fructan hydrolase to give an ethanol yield of ~0.45 g/g sugar.
Using the fresh weight yields of HS-PRG obtainable from established grassland management systems, conservative estimates of fermentative sugar release and conversion from the fibre together with that from the WSC, a total ethanol yield of ~5000 litres/ha/yr is possible.
The Grassohol project is an Aberystwyth University (IBERS) lead research programme with a consortium of 9 industrial partners with the aim of examining the logistic and economic feasibility of utilising high-sugar PRG as a bioethanol feedstock.