A method of production of malic acid, the method comprising: (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from a group consisting of crude maleic anhydride, crude maleic acid, crude fumaric acid, vent gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product to obtain a treated intermediate product by: (i) gas stripping the crude maleic anhydride; or (ii) subjecting a mixture comprising one or more of the crude maleic acid, the crude fumaric acid, and the vent gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon column to substantially remove retained impurities to form the second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) causing the feed to undergo hydration reaction in a tubular reactor or a continuous stirred tank reactor to produce malic acid, wherein the hydration reaction of the feed is in the presence of a catalyst selected from a group consisting of aluminum metal, borate salt of aluminum, and carbonate salt of aluminum. (a) treating a first intermediate product to form a second intermediate product, wherein the first intermediate product is selected from a group consisting of crude maleic anhydride, crude maleic acid, crude fumaric acid, vent gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process, and combinations thereof, and wherein the treating comprises: substantially removing impurities from the first intermediate product to obtain a treated intermediate product by: (i) gas stripping the crude maleic anhydride; or (ii) subjecting a mixture comprising one or more of the crude maleic acid, the crude fumaric acid, and the vent gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon column to substantially remove retained impurities to form the second intermediate product; substantially removing impurities from the first intermediate product to obtain a treated intermediate product by: (i) gas stripping the crude maleic anhydride; or (ii) subjecting a mixture comprising one or more of the crude maleic acid, the crude fumaric acid, and the vent gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and (i) gas stripping the crude maleic anhydride; or (ii) subjecting a mixture comprising one or more of the crude maleic acid, the crude fumaric acid, and the vent gas scrubber solution obtained from a phthalic anhydride production process or a maleic anhydride production process to crystallization; and passing an aqueous solution of the treated intermediate product through a carbon column to substantially remove retained impurities to form the second intermediate product; (b) obtaining a feed comprising the second intermediate product; and (c) causing the feed to undergo hydration reaction in a tubular reactor or a continuous stirred tank reactor to produce malic acid, <EOS>