A method of processing fiber-containing co-products of an alcohol production process, the method comprising: (a) contacting polysaccharide fibers present in a mixture comprising one or more co-products of an alcohol production process with an α-hydroxysulfonic acid to hydrolyze at least a portion of the polysaccharide fibers, thereby generating fermentable sugars and releasing oil from the polysaccharide fibers, wherein the one or more co-products of an alcohol production process comprise one or more of the following: (i) wet distiller's grains; (ii) thin stillage; (iii) whole stillage; and (iv) gluten feed; wherein the concentration of α-hydroxysulfonic acid is 2.0 to 3.5% by weight of the mixture, and the temperature of the mixture is 115 to 140 °C; (b) increasing the pH of the mixture by adding a base to the mixture; (c) contacting polysaccharide fibers in the mixture with enzymes to hydrolyze the polysaccharide fibers, thereby generating additional fermentable sugars and releasing further oil from the polysaccharide fibers, wherein the temperature of the mixture is 50 to 55 °C; (d) incubating the mixture with yeast under anaerobic conditions to produce alcohol by fermenting fermentable sugars produced in steps (a) and (c), wherein the temperature of the mixture is 25 to 35 °C; (e) distilling the mixture to remove alcohol from the mixture, thereby producing an alcohol-containing distillate and enhanced whole stillage; (f) removing released oil from the fermented mixture produced in step (d) and/or from the enhanced whole stillage produced in step (e); (g) separating the enhanced whole stillage to produce enhanced wet distiller's grains and enhanced thin stillage; and (h) drying the enhanced wet distiller's grains to remove moisture, thereby producing enhanced dried distiller's grains (E-DDG) having a total protein content of at least 45% on a dry weight basis and a total fat content of no more than 10% on a dry weight basis. (a) contacting polysaccharide fibers present in a mixture comprising one or more co-products of an alcohol production process with an α-hydroxysulfonic acid to hydrolyze at least a portion of the polysaccharide fibers, thereby generating fermentable sugars and releasing oil from the polysaccharide fibers, wherein the one or more co-products of an alcohol production process comprise one or more of the following: (i) wet distiller's grains; (ii) thin stillage; (iii) whole stillage; and (iv) gluten feed; wherein the concentration of α-hydroxysulfonic acid is 2.0 to 3.5% by weight of the mixture, and the temperature of the mixture is 115 to 140 °C; (i) wet distiller's grains; (ii) thin stillage; (iii) whole stillage; and (iv) gluten feed; (b) increasing the pH of the mixture by adding a base to the mixture; (c) contacting polysaccharide fibers in the mixture with enzymes to hydrolyze the polysaccharide fibers, thereby generating additional fermentable sugars and releasing further oil from the polysaccharide fibers, wherein the temperature of the mixture is 50 to 55 °C; (d) incubating the mixture with yeast under anaerobic conditions to produce alcohol by fermenting fermentable sugars produced in steps (a) and (c), wherein the temperature of the mixture is 25 to 35 °C; (e) distilling the mixture to remove alcohol from the mixture, thereby producing an alcohol-containing distillate and enhanced whole stillage; (f) removing released oil from the fermented mixture produced in step (d) and/or from the enhanced whole stillage produced in step (e); (g) separating the enhanced whole stillage to produce enhanced wet distiller's grains and enhanced thin stillage; and (h) drying the enhanced wet distiller's grains to remove moisture, thereby producing enhanced dried distiller's grains (E-DDG) having a total protein content of at least 45% on a dry weight basis and a total fat content of no more than 10% on a dry weight basis.