Having read the comments from the judges it sounds like the solvent flavours / astringent flavours are very pronounced so would be surprising if you couldn't pick up on it yourself.
Are you serving the beer from a keg or is it bottle conditioned? If you bottled from keg specifically for the competition I'm wondering whether there is something in that process that has exacerbated the issue.
Might be helpful as well if you can describe your end-to-end brewing process so people can see if there is anything that jumps out as a potential cause. I think over the course of the thread almost every logical root cause has been suggested but there may be something we're missing.
Maybe my taste buds are shot :)
My general brew day goes like this:
Wash out the brew pot and bag ( I do biab).
Pour water into the pot to heat, i normaly keep 5l for sparging.
Weight out grains
Weigh out water salts and add to the water ( this i sometimes forget and add after the grain)
When water is at strike temp
Add grain to water mixing while I pour in.
Every 10-15 mins stir and check temp - heating if needed. (Occational over heat - add some cold sparge water if its too high)
Heat sparge water
Clean a colander and big bowl
Lift grain bag by hand and leave to drain, squeezing a bit ( with latex style gloves on)
Put bag into colander and slowly pour the sparge water on.
Turn pot up to boil
Squeeze bag
Add run off into pot
Wait for hot break
Clean up mess left on the counter and wash the bag, colander and bowl.
Measure boil additions (hops) in clean but not sanitised small bowls.
Add additions direct to pot when needed.
Durining mash, wash and sanitise the chiller coil, fermemter, auto-siphon etc.
Using a clean cloth and star san/chem san at correct rate.
I leave the fermenter full of sanitiser.
15 mins before end of boil add chiller.
At end of boil move pot to by the back door to allow pipes to get to the chiller.
Move pot back to stove when cool.
Empty sanitiser into plastic tub, and rince along with bag.
Transfer wort into bag in fermenter.
Lift bag out sometimes squeezing ( this is risky, I wash but don't allways I sanitise my hands here).
Add yeast, closing fermenter and adding to the fridge.
Lots of cleaning at this stage.
Bottle prep goes one of 2 ways either I prep days before and cap with proper caps or the plastic bottle savers I've now got or I'll prep just before and cover with plastic wrap.
If the bottles are new or heavy soiled I'll clean with vwp and a bottle brush and rince twice. If not I'll use chem San and bottle brush and will rince.
Botteling.
Sanitise the botteling wand and a cloth.
Will empty then attach to the tap.
Bottle caps are sat in chem san.
Bottles are capped when full.
Dry hopping:
Hops are weighed in Clean but not sanitised bowls.
Hop socks are sanitised and rinced.
Carbination:
I used to boil water and mix the tabel sugar the add to the fermenter 30mins before botteling
Now I inject 10mm into each bottle before filling.
Hopefully that all makes sense, bar some typos from being on my mobile and some dyslexia spelling oddness :)
