How can I make homemade tofu more flavorful?

You're right in that most of the tofu that we see in supermarkets are the white, super-bland type...the only variation is in softness. If you're a vegetarian, you probably know where to find other kinds that have been baked, marinated, etc.

I really love tofu and one of my favorite kind is a densely packed tofu called "dofu-gan", literally translated as "tofu dry". It is tofu that has been flavored/marinated and pressed so that it has very little water content. These little "dofu-gan" cakes are sold at Chinese supermarkets in clear plastic bags with lettering on them. They generally will come in packs of 4 or 8. Each cake measures about 2" x 2" x 0.5". The texture is similar to super dense gelatin snack...it has a bite.

Usually these are brown in color because they have been marinated. The inside is also slightly brown so whatever marinade has also entered slightly into the tofu. They have different flavors such as soy, and some have a little spice.

So you can potentially go down this road and stay with Asian flavorings...soy, sesame oil, sambal, fish sauce, teriyaki, lemongrass, Chinese BBQ sauce, XO sauce, etc.

Also, I know that the baked tofu, etc. that has targeted vegetarians use marinade flavors that normally would be used for meats...such as bbq flavor, lemon herb, etc. So if you want to go this route, you can potentially do something such as: Tandoori, satay, liquid smoke, etc.

The way that the "dofu gan" is usually eaten, at least when I was growing up is... julienned and stir fried with vegetables and sometimes with thin strips of pork.

ANOTHER kind of tofu preparation is called "dofu-ru" and this IS actually fermented tofu. You can buy these in jars and the tofu is suspended in some sort of liquid. It is really salty. I've only seen it used (in my family) as flavoring for rice porridge and when stir frying spinach or pea shoots. You would add literally a dab and it would flavor the dish. It has a very distinctive flavor/aroma...it's hard to describe. I've never seen this flavored with additional ingredients, but you can try and see what you get.

1- Is this a valid approach and I should just add a lot more of my flavoring agents?

Yes, you can make additions to your curd prior to pressing/knitting just like with cheese. Adding bits of dried peppers ala pepper jack cheese sounds like a great idea. The main concern in this regard is to avoid adding so much adjuncts that the tofu curd fails to knit together during the pressing/draining phase and falls apart as you're handling it during subsequent cooking.

A secondary concern is that tofu generally weeps significantly more water than cheese curds. And since you've added your adjuncts already, part of the flavor of those adjuncts will run off as the tofu curd weeps. The only real suggestion I have for that is to use assertively flavored adjuncts.

2- Are there other flavoring agents that will present themselves more forcefully (and pleasantly) in tofu?

Soy beans have fat in them. The fat in the beans becomes emulsified in the milk when processing the beans into soy milk. The majority of that fat ends up in the soy curd when curdling the soy milk. The majority of the fat in the soy curd will remain in the curd during pressing/knitting into tofu blocks.

You can use this to your advantage. When grinding the soy beans into milk, you can fat based flavoring, some of which will end up in the soy milk, some of which will end up in the resulting curd, and thus into the tofu blocks. If your fat based flavoring is particularly intense, then it should be noticeable in your tofu blocks. A common type of intensely flavored (aromatic) fat based flavoring is essential oil. You can add essential oil of lemon or orange and that flavor will certainly carry through into the final tofu blocks.

3- What easily accessible bacteria would be able to ferment soy curd in a pleasant way?

Fermented tofu/bean curd has been made for centuries. There are number of fungii strains commonly used to ferment bean curd. There are likely many other bacteria that could be used. Lactic acid bacteria could feasibly grow in tofu/bean curd, though I'm not sure a sour tofu is something I'd personally enjoy.

Aside from blocks of tofu/bean curd, there is also a long history of fermented products with amazing flavor that use soy beans but not in a curd/block form. There is tempeh, soy sauce, koji, miso, etc.

I am reviving this q/a because this year a book all about making your own tofu, Asian Tofu by Andrea Nguyen, has been released and it has a few ideas for flavoring your own tofu. Namely, she mentions a traditional Japanese infusion of yuzu into the tofu. Another traditional option is seaweed.

More similar to cheese would be misozuke (a general recipe of which can be found at Rau Om). Misozuke involves taking finished tofu and wrapping it in a miso and flavoring mixture and letting it ferment. The tofu becomes soft, like a soft cheese, getting softer the longer it sits. You can try it from two days to two months. Adding flavor to it is a matter of wrapping or smearing it with additional ingredients, like seaweed.

I add salt to the soy milk before I add the coagulant to separate the curds.

It is true that even in cheese making, if you add vinegar or lemon juice to the hot milk to curdle and break into curds and whey, the sourness of the vinegar or lemon do not get bound up in the curd but either neutralize or stay with the whey. The same thing to a degree would happen with salt or similar seasonings, that some would stay in the whey. So perhaps adding more than you believe you would want in your tofu curd would be right since some must go out with the liquid that separates from the tofu curd.

Interesting idea to go with flavors that will combine readily with fats. But adding fats or flavored fats such as chili oil into the soy milk might change the way curds break out or bind into a cake. Good thing you have lots of soybeans to work with. Tireless trial and error is the mother of invention!