The general cooking recipe of soybean-based foods in East Asia includes a soaking process for 6 or 18 h in water, depending on the season. In the present study, the treated concentration of organic acid was determined by the degree of the discoloration of the soybeans. When organic acids higher than 1.0 N were added to the soybeans, the discoloration occurred. The reduction rates of AFs in the contaminated samples with distilled water and organic acid solutions such as citric acid, lactic acid, succinic acid, and tartaric acid during the soaking process were shown in Table 2. The reduction rates of AFB1 in distilled water (control) for 6 h and 18 h were 58.1% and 62.0%, respectively. The reduction rates of AFB1 in all 1.0 N organic acids for 6 h and 18 h were significantly different from the reduction rates in distilled water, except for 1.0 N succinic acid (p < 0.05). The reduction rates of AFB1 in 1.0 N citric acid and 1.0 N tartaric acid for 18 h were 94.1% and 95.1%, respectively. However, the mean of the reduction rate of AFB1 during the soaking process with 1.0 N succinic acid was 58.5% for 6 h and 62.0% for 18 h.