[snax]

I switched to all grain years ago but came upon a recipe that i really wanted to try.  However, it is an extract recipe with steeping grains.  I brewed it twice and got a plastic off flavor both times.  I use un-adjusted R.O. water and nothing but StarSan touches anything once I start brewing so I know it's not chlorine.  I used White Labs WLP001 which I have used several times before with no issues.  The only thing I can think of is my plastic fermentation bucket but, again, I have used it before and since without issue.  Any help out there?

When you say RO water, is it from your own 3 or 4 stage in home filtration system, or a "water mill" at the local grocer? Do you test the water pre-brewing to assure that all/most of the free and/or total chlorine was removed by carbon filtration prior to the RO membrane?

Water from those machines at the local grocer is only as consistent as the technician is in servicing them, especially during high use. I'd tested RO water from a machine and the pH was the exact same as our tap water (9.4) when it should have been much lower if the system was functioning properly.