Cooked Corn and Popcorn on a Fresh Pilsner Keg

Defect 1 - "cooked corn / creamed corn": DMS (dimethyl sulfide). Threshold in a light lager is on the order of 30–50 ppb - which is why Pilsner is the most unforgiving beer in the brewery. DMS comes from S-methyl methionine (SMM), a precursor concentrated in Pilsner malt. SMM is heat-labile: it is driven off by a long, vigorous, uncovered boil and by rapid chilling.

Match to notes: the kettle lid was partly on for the last 20 minutes - that traps DMS vapor that should have left the stack. A 60-minute boil is nominal-to-short for a 100% Pilsner-malt grist; 90 minutes is standard practice. The 20-minute whirlpool also holds the wort hot with the lid back on, and a 36-hour crash means a slow, warm chill that lets residual SMM convert.

Defect 2 - "movie popcorn": diacetyl (2,3-butanedione). Threshold is famously low, roughly 0.1 ppm (100 ppb), and it reads as butter, butterscotch, or slickness. Diacetyl is a yeast byproduct of valine synthesis; it is reabsorbed and reduced to acetoin/2,3-butanediol by active yeast during a diacetyl rest.

Match to notes: fermented at 50°F and then crashed to 32°F in 36 hours. There is no diacetyl rest and no time at 55–60°F with yeast still in suspension. The crash arrested the reduction step mid-way and locked the precursor in the keg.

Rule them out methodically - that is what protects the relationship with the brewery.

• Line contamination: unlikely. Acetobacter or a dirty line reads as vinegar, musty, or sour-dirty, not buttery or corny. Lines cleaned 3 weeks ago is within a normal 2-week-to-4-week cycle, and the defect appears on exactly one tap. If it were a line issue, you would expect it localized but with a microbial character.
• Temperature: ruled out. Glycol at 34°F with a 38°F target means the beer is cold and stable; warm beer does not create DMS or diacetyl, and it does not create them in 48 hours.
• The 95°F loading dock: contributes but is not the cause. Six hours warm will accelerate staling and can spike diacetyl if live yeast is still present in the keg, which is consistent with a brewery that packaged without a rest. Call it an aggravating factor, and cite it - but do not let it be the headline, because DMS cannot be created post-packaging.
• Glassware: check one anyway. A rinse-aid residue reads as soapy/flat and can be mistaken for slickness.

Verdict: both defects are brewhouse and fermentation failures that were present in the keg before it reached you. Your line is clean and your system is cold.

Tonight:

1. Pull the tap and mark the keg "hold." Do not dump it - you may need to return it or sample it with the brewery.
2. Pour a sample at the bar and at the tap and taste both, noting that hop aroma is also suppressed (a Pilsner at 35 IBU with no hop nose is another data point pointing to the boil).
3. Replace with another Pilsner or a pale lager on that line so regulars are not served a defective beer. Hold the line with a cleaning and a water flush.
4. Do not "fix" it. There is no fining, venting, or temperature trick that removes DMS from a keg.

To the brewery, in writing:

• Batch number, keg serial, tap date, and the exact sensory descriptors plus when they were detected (48 hours after tapping, not on the first pour).
• Note that only this tap is affected, lines were cleaned 3 weeks ago, glycol verified at 34°F - take those off the table proactively.
• Cite the 6-hour 95°F dock exposure factually, as an aggravating factor.
• Ask two specific questions: boil length and whether the kettle was covered, and whether a diacetyl rest was run before crashing. Those two answers resolve the dispute in one exchange.