It's most likely the water. It's from chlorine reacting with constituents of the malt to form something called chlorophenols. If you didn't treat your water for chlorine, then this has got to be it. And fortunately, it is very very easy to get rid of chlorine in your water in the future. Before you begin your mash, all your water needs to be treated either through carbon filtration or even easier is 1/4 Campden tablet per 5 gallons, crushed and added to your water immediately prior to use. Then this will never happen again!!dmtaylor thank you for your insightful answer to my problem. I am assuming this will not go away with age int eh beer so my only alternative is to throw the batch that I bottled away and start over right? Damn, I am finished with two books out of the four of water yeast hops and malt, unfortunately water and yeast are left to read. Oh well live and learn. I have not noticed this in any of the other beers I have been brewing, is this only a symptom of Hef's? as I have brewed stouts, pilsners, american ales, IPA's etc. with no off tastes like this.
Are you using city municipal water? It can change over time. I know a guy who works for our water system in my city and he says they chlorinate heavily twice per year in the spring and the autumn. Your own city's schedule could be similar, or entirely different. But it is possible that on this batch you hit a chlorine surge. That's what happened to me 15 years ago when I began to use Campden. Before that, I was just lucky.
Another reason it might be specific to this batch is that the WLP300 yeast generates a lot more phenols than normal yeasts. These phenols actually taste great, like cloves. However, once the phenols combine chemically with chlorine to form chlorophenol, it will taste like medicine.
And yes, it is irreversible. You might indeed need to dump this batch and start over.