Help with this off flavor?

My brother brewed a Brewers Best Pumpkin porter about 6 weeks ago on our gear while I was on vacation and it has an off flavor I'd like to avoid in the rest of our brews.

Sharp hot taste right in the front of the beer, that goes away quickly into a pretty average tasting porter. The beer may taste slightly metallic, but it's nothing compared to the off taste right in front. Ideas? Ambient air during ferment was around 68-70. 3 weeks in primary, two in the bottle. Only brew issue he noted was adding to much water to the wort and having a low OG. (around .005 low)

Sounds like "Hot Alcohol" or what the BJCP calls "Alcoholic". Your fermentation temperature looks ok. You may not have oxigenated the wort enough or you may have pitched too little yeast.

For proper pitching rates visit Mrmalty.com

If it's an alcohol taste, that can mellow given time. I've got a 3 year old barley wine that used to have than kind of alcoholic bite, but it got better.

Sounds like fusel alcohols, petentially caused by higher-than-ideal fermentation temps. If your ambient air temps were 70°, you could have been anywhere from 73-77° in your actual wort. While this temp would definitely speed up most fermentations, it can also yield fusels, as I noted with my first brew a couple months ago. I fermented it at room temps very close to yours, per the kit instructions, before I knew the importance of temperature control. It had a pretty "hot" taste, like cheap vodka, for the first month or so. It was drinkable, and the hotness faded slightly over the next few weeks, but I drank it all up before the taste had completely disappeared.

To really be sure, we'd need to know more about your recipe and specific processes for brew day. My guesses would be pitch rate (depending on what yeast you used) or fermentation temps.

Pumpkin and darker beers may take more time anyway,besides 2 weeks is too early to worry about anything anyway.More time should make it a better beer. I havnt had a pumpkin porter yet, that sounds good. Ive found if i ferment at the high end of temps the longer it takes for them to condition any kind of offishness.I would check one in three more weeks,or months.

I'm letting the batch bottle condition now, i'll keep trying a bottle every month or so. Thanks for the suggestions