A process for producing sugar monomers and/or polymers from a carbohydrate-rich substrate, said process comprising the steps of: (a) providing a reaction mixture comprising a carbohydrate-rich substrate and a liquid solution containing a hydrolysis catalyst by mixing the hydrolysis catalyst with process water using turbulent energy to produce a homogeneous mixture, wherein the hydrolysis catalyst is selected from (i) an organic acid, a mineral acid, hydrogen peroxide or mixtures thereof (ii) one or more Fenton or Fenton like reagents, or (iii) one or more enzymes with cellulolytic and or hemicellulolytic activity, and maintaining a gas pressure above said carbohydrate-rich substrate at an evacuation pressure of from 105% to 200% of water equilibrium pressure at infusion temperature and for 1 minute - 2 hours to infuse said hydrolysis catalyst into said carbohydrate-rich substrate at an infusion temperature of 40-90°C; (b) exposing said reaction mixture to a gas-phase reaction pressure of 50-150 kPa that is higher than said evacuation pressure; (c) maintaining said reaction mixture at a reaction temperature of 15-95°C for a reaction time of 15 minutes to 8 hours to generate said sugar monomers and/or polymers within lumen space of said carbohydrate-rich substrate; (d) exposing said reaction mixture to a gas-phase expulsion pressure that is lower than said reaction pressure, wherein said expulsion pressure is from 100% to 200% of the water equilibrium pressure at said reaction temperature; (e) maintaining said reaction mixture at an expulsion temperature of 15-95°C for an expulsion time of 1 second to 60 minutes; (f) repeating steps (b) to (e) for at least two pressure cycles to expel said sugar monomers and/or polymers out of said lumen space and into said liquid solution; and (g) recovering said sugar monomers and/or polymers from said liquid solution. (a) providing a reaction mixture comprising a carbohydrate-rich substrate and a liquid solution containing a hydrolysis catalyst by mixing the hydrolysis catalyst with process water using turbulent energy to produce a homogeneous mixture, wherein the hydrolysis catalyst is selected from (i) an organic acid, a mineral acid, hydrogen peroxide or mixtures thereof (ii) one or more Fenton or Fenton like reagents, or (iii) one or more enzymes with cellulolytic and or hemicellulolytic activity, and maintaining a gas pressure above said carbohydrate-rich substrate at an evacuation pressure of from 105% to 200% of water equilibrium pressure at infusion temperature and for 1 minute - 2 hours to infuse said hydrolysis catalyst into said carbohydrate-rich substrate at an infusion temperature of 40-90°C; (b) exposing said reaction mixture to a gas-phase reaction pressure of 50-150 kPa that is higher than said evacuation pressure; (c) maintaining said reaction mixture at a reaction temperature of 15-95°C for a reaction time of 15 minutes to 8 hours to generate said sugar monomers and/or polymers within lumen space of said carbohydrate-rich substrate; (d) exposing said reaction mixture to a gas-phase expulsion pressure that is lower than said reaction pressure, wherein said expulsion pressure is from 100% to 200% of the water equilibrium pressure at said reaction temperature; (e) maintaining said reaction mixture at an expulsion temperature of 15-95°C for an expulsion time of 1 second to 60 minutes; (f) repeating steps (b) to (e) for at least two pressure cycles to expel said sugar monomers and/or polymers out of said lumen space and into said liquid solution; and (g) recovering said sugar monomers and/or polymers from said liquid solution.