Tasting stout 1.5 weeks into fermentation

That could be a number of things. Probably though, you are just tasting it too early. The yeast has lots of cleaning up to do still. Give it another week if you can wait that long, and try it again.

The sharp alcohol aroma does sound potentially like it could be a fermentation problem though. If you pitched your yeast into too-warm wort, or there were temp fluctuations, or it fermented too warm, or didn't pitch the correct amount of yeast, or you waited too long before pitching and bacteria grew in there... those could be issues. Do any of those ring a bell?

And astringency might possibly be due to old stale oats. Were your oats pretty fresh, or unknown? I've had some yucky issues with old oats, due to their high lipid content, leading to some pretty gross off flavors. Nobody seems to know about this but it's a serious issue, especially if they're stored in a warm room.

 

A flat fermenter sample really has no correlation to a carbed and properly aged sample. Let it ride another week. Carb and try again.

 

Please, describe your brewing procedure.

 

I'm with PDX and kellyst - let it go for a bit longer. I used to sample my RIS about 1.5 weeks in when I did gravity readings and it always had a gross quality to it that resembled a yeasty 'bite'. Maybe that's the astringency you're referring to? It could be just off tasting byproducts from a vigorous fermentation. I use the chico strain on mine. Given the right amount of time in the fermenter though the yeast will do a lot of cleaning up.

 

Your beer still has a long time before it's meant to be consumed. If it is bad, there is nothing you could do for it at this point. Just forget about it for another week and a half and move it to keg / bottles after making sure fermentation is done.