re: Question for Statistics Gurus

The process you are doing is correct.

Cross-validation is definitely the way to go with a regression problem like this.

If you are concerned in trying to find the difference between a true outlier and an something that would be considered wrong because of the process I would look at the r-studentized residuals.


ETA: If you want I can give you a reference to a professional statistician I know who loves this kind of stuff. Actually works with professors in Food Science on similar issues to yours.
These type of residuals are similar to z-scores.

If you have rstudent values over ~+/- 2.5 that means that the value the regression predicted had only a P(Z>=2.5) <0.0001 chance of being replicated again.