Specifically, orange juice and soy sauce, but I suspect my difficulty is universal to any citrus, some sort of chemical reaction from the salt in soy sauce, sugar and citric acid. I simmer fresh squeeze OJ with soy sauce and a bit of sugar. I keep tasting as it reduces, like every five seconds, happy as it sweetens and thickens, and then BAM! the next taste is the most sour thing to have ever touched my tongue. It's like there's some sort of hardline tipping point. If anyone can explain what's happening, how to detect/anticipate this sudden transition from sweet to sour, or any basic sauce recipes for orange and soy, thanks!