Can I cook and taste the food while fasting?

This is a practical question rather than a theoretical one: a great deal of cooking happens in Ramadan, often while hungry, and often for other people.

• Cooking does not affect the fast at all.
• Smelling the food does not either. The nose is not a route to the stomach.
• Tasting with the tip of the tongue, without swallowing, and spitting afterwards, is permitted when there is a reason — adjusting a dish you are about to serve to others. Doing it for pleasure is discouraged, not because it invalidates, but because it brings you unnecessarily close to what would.
• Swallowing unintentionally does not invalidate.

The boundary is set by the same verse that fixes the hours: “It has been made permissible for you the night preceding fasting to go to your wives for sexual relations. They are a clothing for you and you are a clothing for them. Allah knows that you used to deceive yourselves, so He accepted your repentance and forgave you. So now, have relations with them and seek that which Allah has decreed for you i.e., offspring. And eat and drink until the white thread of dawn becomes distinct to you from the black thread of night. Then complete the fast until the night i.e., sunset. And do not have relations with them as long as you are staying for worship in the mosques. These are the limits set by Allah, so do not approach them. Thus does Allah make clear His verses i.e., ordinances to the people that they may become righteous.” (Qur’an 2:187)

One thing worth pointing out, because it surprises people fasting for the first time: a good part of Ramadan happens around food. You cook, you shop, you prepare the iftar, you serve others. That is not a contradiction of the fast; it is part of it. Feeding someone you break the fast with is among the most praised things in the month.