In a large pot, add the corn and enough water to cover it by double (8-10 cups). Stir in the cal and bring the water to a low boil. Let cook, stirring every 5 minutes to check the water content, until the corn is al dente (when broken or bitten, the center of the kernel will still be slightly white) and the silky skins slip off easily when rubbed between fingers, 5-20 minutes. Turn off the heat and add water as needed to cover the corn by 2 inches. Cover and let rest at least 8 hours and up to 16 hours (corn will have swelled in size and may have changed color).
Transfer to a strainer and wash the corn under cold running water, rubbing it vigorously between your hands, until most of the skins have come off and the kernels look shiny (don't use a fine-mesh strainer, as you want the skins to fall to the bottom of the strainer or slip away through the holes). Use the corn immediately or store fully covered in fresh, cool water for up to 1 day in the refrigerator.
Grind the corn on nearly the tightest setting in a molino de mano (hand-operated corn grinder), pouring 1-2 teaspoons water over corn as needed to help it slide through the grinder. Tighten the setting all the way and repeat the grinding. If making tortillas, grind the masa once more in a stone grinder (metate) to get a fine, smooth consistency. Season with salt and add small amounts of water only as needed to reach a moist but not sticky consistency. Chill in a roomy container and use within 2 days. Bring to room temperature before using.