Less than adequate sanitation practices, old expired sanitizer, scratched plastic, or rubber components can all lead to permanent residence of wild yeast or bacteria. In the case of vomit aroma or flavor, I believe the source is bacteria. I have experienced this one time. The resolution is to throw away any and all plastic and rubber components, including hoses and gaskets, start over with new stuff, and ensure everything is sanitized to the utmost degree. Also consider moving towards to glass or other hard materials, and thus minimize the possibility of places for wild critters to hide out.
Don't be surprised. It happens to most of us eventually.