Health rules to cook vegetables:

1. All green vegetables should be cooked in an amount of boiling water which is enough to cover them except for spinach, which should be cooked without water due to the high proportion of water in its leaves. You may add a little bit of water, a large spoon of salt, and one gallon of water (4 liters) to improve the taste and to help raise the temperature of the water which maintains the color of the vegetables.
2. Vegetables should be cooked quickly along with removing the foam whenever it appears so as not to affect the color. Soft-structured vegetables such as the gourd, cauliflower, and artichokes should be cooked on medium heat to prevent the rupture of their parts. When boiling cauliflower, the flower should be put down to prevent the gathering of the foam on the surface and changing its color.
3. Cook vegetables in a reasonable amount of boiling water on a hot fire while covering the cooking pot. The amount of water is estimated at about half the weight of the vegetables.
4. Cook green vegetables in an uncovered pot with a quantity of water sufficient to cover the vegetables, and this makes the color brighter. Green vegetables are strongly affected by acids, and since vegetables contain non-volatile acids, it is not possible to totally avoid the change in their green color. To avoid it as much as possible, cook the green vegetables in an uncovered pot so that the acids fly with the vapor and do not affect the chlorophyll (the green pigment in plants). If the cooking method requires the pot to be covered, you must leave the vessel without a cover in the first minutes in which the volatile acids frequently fly.

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