Lemon juice and vinegar are good examples. We also eat certain bases, although they are not as common as acids. Baking soda, for example, is a base when it is dissolved in water. Tasting is not a test used by chemists to determine whether or not a substance is an acid or a base. Instead, they use a dye called an indicator that changes color depending on what the solution is.
Litmus paper turns blue when it is dipped in a base and pink when it is dipped in acid.
Here's how to make some red-cabbage indicator. Grate it secton by section into a large bowl. Add between 1 and 2 cups water, enough to cover the cabbage. Let the cabbage stand in the water, stirring occasionally so that all the cabbage is moistened . When the water is a strong red, remove as much of the grated cabbage as you can with the slotted spoon and save it in your second bowl.