I have done a Steam Ale, Pale Ale, IPA, Blonde, Cream, and a Pumpkin Holiday Ale proir to this. The beer that has the plastic taste is an Oktoberfest. All of these beers have been run through the same tubing/plastic equipment and this is the only one that has tasted like this. I clean my equipment by rinsing and using soap and water where necessary, and then sanitize. I use use C-Brite sanitizer which requires me to rinse after, which I do.
Sounds like you have a phenols problem....First off I'd dump using the c-brite or other rinse requiring sanitizer in favor of a no-rinse like iodophor or starsan. For 2 reasons; 1) unless you are rinsing with Distilled, boiled or Bottled (sterile) water you run the risk of introducing any bacteria from the sink or from the water into/onto your equipment. and phenols possibly can be casued by bacteria, often lurking in the hoses...A no rinse like starsan is good for preventing this becasue the foam can reach hard to reach places, like in hoses. (although I use iodophor, which I pump through my hoses...that works too)
Wild yeast contamination can harbor within plastic-based equipment, such as polyethylene fermenters and plastic hoses. These materials as soft and permeable, hence difficult to clean. Wild yeasts such as S. diatatius produce minor wort phenols that impart medicinal off-flavors.
2) Phenolic flavors can also be caused by Chlorophenols which exist in municipal water supplies and residue from chlorine-based sanitizers. They can affect beer in parts-per-billion (ppb)! Avoidance of both should be given; find a substitute water supply and avoid chlorine-based sanitizers altogether.(Is c-brite a chlorine based sanitizer?)
Also;
if you are doing extract with grains, don't let your grain temps go above 170 and never boil your grains...Tannins sometimes are described as plasticky.
Phenols are also derived from certain yeast strains that produce aromatic alcohols. Bavarian wheat beers produce acceptable levels of phenols. It could be simply the yeast you are using in your Oktoberfest, what type is it?
Here's a good article on Phenolic tastes in beer from BYO...
http://byo.com/mrwizard/743.html
Check on your beer in a couple more weeks....if it hasn't faded then it probably is phenols, which means if you don't like it you might want to scrap the batch....
But hopefully we can stop it for the future.
