Stouts always taste funny

Somewhat new brewer here. I have about 10 all grain brews under my belt. I recently made my 3rd stout and just like the first 2 it has a strange aftertaste that is hard to describe. However if I brew a lighter beer such as a pale ale or hefeweizen I do not get this taste and they always turn out perfect. I’ve tried using 100% rodi and also 50% tap and 50% rodi. I always use campden tablets so chlorine isnt an issue. I thought maybe in my previous brews my sparge water was too hot so I made sure it was a bit cooler this time and still has a strange taste. Any advice would be appreciated.

Can you describe the funny taste?  My first thought is pH issues.

It’s hard to describe. I’ve read a few articles about common off flavors in beer and none of them really describe what I’m getting. The best way I can describe it is like a musty metallic taste or smell. Like food that has been in a can for too long.

Not really a lot to go on, but based on context (only in dark beers) I would hazard a guess that it has something to do with the dark grains.  I think Denny might be onto something with pH. Darker grains are more acidic and so that metallic type off flavor could be from low pH (a “tang” if you will).  Dark grains can also be acrid or bitter, so that aftertaste could be from too much roast bitterness like a dark roast coffee or burnt toast.

Are you using high amounts (10%+) of really heavily roasted grains, like Black Patent (500 lovibond or more).  Those grains in high amounts tend to be very harsh, sometimes with burnt flavors like an ashtray or smoke.

Low pH could also stress the yeast, so they might throw off flavors from that as well. Are your stouts high alcohol? Underpitching with a low pH wort with lots of unfermentable sugars could be messing up your yeast.

Based on the info you’ve given I’m leaning toward pH as well. The darker grains lower pH considerably more than the lighter ones. Since your results are the same with RO and tap water I would be led to believe that your tap water is very low in mineral content.

Lacking any solid information about your tap water I’d advise using RO and a water tool like Bru’n Water to build water that closely suits the style. An alternative, as much as I hate to recommend adjusting water without having a baseline to start from, you might try adding  a teaspoon of baking soda to your strike water next time you brew this beer.

I think I know what you’re describing. My stouts generally have what I can only describe as a subtle, minerally, baking-soda “saltiness,” which I can see could be fairly described as a (slight) metallic tang. I do add some baking soda to my mash to increase alkalinity, but I’m not sure the flavor is coming from that. As other brewers indicate, I think it’s related to the roasted grains–but for me, I love this flavor and mouthfeel because it adds texture to the roast/smoke/ash flavors. So IMO it’s a flavor to be embraced, not a problem to be avoided. Try to get your hands on commercial stouts and see if you taste the same thing.

Be careful with adding alkalinity. There was a mention of adding a teaspoon of BS, but no indication of batch size. Don’t go overboard.

Good point Martin. I just assumed a5 gallon batch.