What is the best source of oxalic acid?
                                
                                
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                                    3 min read                                
                            
                                According to the U.S. Department of Agriculture (USDA), spinach is particularly rich in oxalic acid, containing a much higher concentration than most other crops. The best source of oxalic acid, however, depends heavily on the intended use, distinguishing between natural, dietary sources and more potent commercial products.