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1.
to turn soymilk into tofu by adding nigari (magnesium chloride) or calcium sulfate. it is also achieved on a home scale by adding an acid such as vinegar or lemon juice to create a substitute for buttermilk in recipes.

and finally, it unintentionally happens when adding cold soymilk to hot coffee, which creates curdles and little tofu-y bits. (this can be avoided by putting the soymilk in the bottom of the mug and slowly adding the coffee to cook/acidify the soymilk slowly, which creates far smaller particles of tofu.)

see also tofuification

origination:
tofuify first appeared at vegsource by alextree August 29, 2002
tofuification first appeared in a post at livejournal's vegancooking community by postpunkjustin 2007-06-24
you must first tofuify your soymilk before adding the rest of your liquid ingredients. when all liquids are combined, you may add the dry ingredients and incorporate.
by supercarrot February 12, 2010