Undercooking tofu causes a bad stomach. Is this true? My girlfriend, who is Japanese and has thus eaten and cooked a lot more tofu than I have, says that tofu should either be eaten "raw" or well cooked. To be half and half will cause a bad stomach. She last said this to me when I said I only added silken tofu to miso soup just before I eat it.

However, in the last year I started to make my own tofu, so I know that the last heating of the soy milk makes it digestible. Then, for example with silken tofu, the soy milk is steamed/cooked in a bain-marie to produce the silken tofu. So from my experience of eating it with miso soup I've never had a bad stomach (because I'd assume dropping it into hot soup would constitute undercooking) and from my knowledge of the process it is rendered edible at the milk stage.

However, tofu is so ubiquitous in Japan that I find her input hard to dismiss. Does anyone have any insight that would help clarify this.
Firstly…  Do you think your girlfreinds may simply be worried about being gassy from eating beans? 



It is a misnomer that tofu is ever technically “raw” because because all the ingredients for making tofu are cooked (brought to a simmer or boil) in the manufacturing process.

The soymilk is often cooked twice when making tofu: first when making soymilk from soybeans and second when making tofu from the soymilk. (However the process of making silken tofu from soymilk does not always involve a second step with high temperatures.)

Some possible reasons that tofu could cause a bad stomach:


tofu is past it’s expiration date.
tofu was not refrigerated properly.
tofu is somehow contaminated.
allergies to soy.
eating beans can cause gas.


If it's the gas, try fermented soy products (such as tempeh) which cause much less or no gas.

References:


http://www.seriouseats.com/2011/08/how-to-make-fresh-silken-tofu-from-home.html
http://www.seriouseats.com/recipes/2011/08/fresh-silken-tofu-recipe.html
http://www.veggieboards.com/forum/21-general-food-discussions/14467-raw-tofu-safe-eat.html
https://www.westonaprice.org/health-topics/soy-alert/soy-carbohydrates-the-flatulence-factor/
https://therightplan.com/tofu-does-not-equal-eating-healthy/