A new beer with a hint of soy

According to my experiences, there are only two ways to get a soy aroma in a clean beer (i.e. without using sake yeast) without adding soy sauce: Yeast autolysis and some dark malts. I wouldn't really recommend going the first route because yeast cell contents can also add other, less pleasant, aromas such as fecal matter. The latter requires some degree of trial and error but I have "sucessfully" gotten soy-sauce type flavors from cold steeping dark crystal malts (Caramunich III, Special W) and from some roast malt (Carafa I) over extended periods.

do you want to just add soy sauce (would that be pretty salty?) to the beer or do you mean brewing with soy beans?

If it is the latter I know the same mold used for brewing sake is used for fermenting soy beans so you could buy a sake kit with the aspergillus spores and inoculate a bunch of steamed soy beans with it. After the mold has grown for a week or so you could add the beans to a cooled wort. This could be a pretty interesting experiment.

My first recommendation for this type of flavoring experiment, is to go commercial. I'd go get 4-5 different commercial beers of different styles (pilsner, Amber, brown, Pale, stout or porter) and add soy to it. If we are talking about soy sauce then I'd just pour a 2-4oz sample of beer and add a few drops of soy sauce to it until it has that "hint" of flavor you are looking for.

Doing it this way will help you decide (through clever math) how much soy sauce to add to a 5 gallon batch. And you'll also get to experiment with different style with soy.

You might find out that it doesn't work with any style and that you'll just scrap the experiment. That way you won't ruin 5 gallons first.

I would plan to add my soy flavoring to the secondary post fermentation. And just scale it up from how many drops worked well in a 4oz sample.

Hope that helps.