Here's what I do when I buy tofu at the grocery store: I put it in the back of my fridge and forget it for at least three days.
Then, when I'm remember that it's there, I make a slit in the corner and press all of the liquid out in a very satisfying release of pressure. I cook what I want, then put the rest in a glass container. Back into my fridge it goes!
Does hearing that make you want to give me a scolding? Because I deserve one.
I learned from Minh Tsai of Hodo Soy that tofu should be treated like fresh flowers. Rinse the tofu and then—here's where the flower analogy comes in—replace the liquid with fresh water, daily. Clearer liquid means fresher tofu. (According to Minh, that's why grocery store tofu is packaged in opaque, rather than translucent, containers—otherwise, shoppers would notice the cloudiness of the liquid.)
The freshest tofu, of course, is the tofu you make yourself. But to make it, you'll need a tofu mold, the proper coagulant (calcium sulfate for Chinese tofu; magnesium chloride for Japanese), and a whole lot of high-quality soy milk (or a whole lot of soy beans, if you're planning to make the milk yourself, too).
Minh has calculated that, in Hodo Soy's facilities, it takes 25 pounds of soymilk to make 10 pounds of tofu; at home, it might cost you $28 in ingredients to make one store-sized block. You'll get more tofu for your buck if you make silken tofu, as the whey doesn't get pressed out in the process.
In the end, it's probably more economical to seek out high-quality, good-tasting tofu than it is to seek out high-quality, good-tasting, protein- and fat-rich soy milk, and then transform it into a block.
Just make sure to change the water!
Have you made tofu at home? Would you do it again? (Are you a tofu delinquent like I am?) Tell us in the comments.