In a forest based biorefinery, pulp and paper are the main products, while side-streams are utilized for value-added products. One biorefinery concept is to remove hemicelluloses from wood by extraction prior to pulping and converting them into biofuels or chemicals. This study presents a concept of a larch wood based biorefinery and focuses on the mass balance of pre-extraction. Sugar rich extracts were obtained by hot water extraction of Siberian larch (Larix sibirica Lebed.) wood chips at different temperatures and times. At 160°C and 60–90 min the extract contains 13–16% hemicelluloses (on wood). The composition of extracts and extracted wood has been determined to have a basis for mass balances. Fermentation of the hydrolyzed extract with Bacillus coagulans MXL-9 resulted in consumption of all C6 and C5 sugars and produced lactic acid in high yield. In an earlier work, it was demonstrated that water pre-extraction of larch chips followed by polysulfide-anthraquinone (PSAQ) pulping still produced a good papermaking pulp at a yield comparable to the corresponding non-extracted kraft pulp. Accordingly, the present results show that a larch wood based biorefinery has a potential for industrial application.