NOVELTY - Converting a cellulosic feedstock to at least one chemical compound, involves: a) processing feedstock to form first juice/first solid comprising cellulose/hemicellulose; b) hydrolyzing first solid to form first liquid comprising sugar and second solid comprising cellulose; c) separating in separation apparatus first liquid from second solid; d) fermenting sugar to form first mixture comprising chemical compound; e) saccharifying in presence of first fermentation mixture at least part of solids portion; and f) fermenting second mixture to form second mixture comprising chemical compound.    USE - For converting a cellulosic feedstock to at least one chemical compound such as ethanol (claimed); of for conversion of feedstock materials such as cellulosic feedstock materials into compounds such as ethanol which is used as fuels for internal combustion or other engines, as solvents, and as chemical building blocks for the manufacture of other chemicals and polymeric materials.    ADVANTAGE - The process reduces the need to stop and clean apparatus and accordingly can be carried out in continuous mode, e.g. for periods of several days or longer (e.g. a week or more) to support an overall continuous process.    DETAILED DESCRIPTION - Converting a cellulosic feedstock to at least one chemical compound, involves: a) processing the feedstock to form a first juice and a first solid comprising cellulose and hemicellulose; b) hydrolyzing at least part of the first solids to form a first liquid comprising at least one sugar and second solid comprising cellulose; c) separating in separation apparatus first liquid from second solid to form a first liquid portion comprising sugar and a solids portion comprising cellulose; d) fermenting at least part of the sugar in the first liquid portion to form a first fermentation mixture comprising chemical compounds; e) saccharifying in the presence of at least a portion of the first fermentation mixture at least part of the solids portion to form a second mixture comprising sugar; f) fermenting at least a portion of the sugar in the second mixture to form a second fermentation mixture comprising chemical compounds; and additionally: i) washing second solids with at least part of the first juice; ii) adding at least a part of the first juice to solids portion exiting the separation apparatus; iii) combining in a slurry vessel at least a part of the first juice with at least a part of the solids portion comprising cellulose; iv) saccharifying solids portion in the presence of at least part of the first juice; and v) and fermenting sugars in the second mixture in the presence of at least part of the first juice.