Answer
Wa `alaykum As-Salamu waRahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
There is nothing wrong with tasting the coffee when you are fasting because you need to do that. But you have to be very cautious and make sure that nothing reaches your stomach.
Answering your question, the Fatwa Center at Islam Q and A, states:
If a fasting person needs to taste the food whilst fasting, there is nothing wrong with that, and it does not affect the fast so long as none of the food enters the throat of the fasting person. This applies equally to coffee and other things.
If one tastes it without any need to do so, this is makruh, but it does not invalidate the fast.
Ibn Abbas said: “There is nothing wrong with tasting what is being cooked or whatever.”
Imam Ahmad said: “I prefer that he should avoid tasting the food, but if he does that, it will not affect him and there is nothing wrong with that.” Al-Mughni, 4/359.
Ibn Taymiyah said in al-Fatawa al-Kubra (4/474):
“Tasting food is makruh if there is no need to do that, but it does not break the fast.”
Ibn Uthaymeen was asked in Fatawa al-Siyam (p. 356): Is the fast invalidated by tasting food?
He replied:
“The fast is not invalidated by tasting food so long as one does not swallow it, but you should not do that unless there is a need for it; in that case if a little of it reaches your stomach by accident your fast is not invalidated.”
We read in Fatawa al-Lajnah al-Da’imah (10/332):
“There is nothing wrong with a person tasting food during the day when fasting, when there is a need to so that, and his fast is valid if he does not deliberately swallow any of it.
If the taste or smell remains, that does not affect the fast, so long as you do not deliberately swallow anything.
Ibn Sireen said: There is nothing wrong with using a wet siwak – i.e., when fasting. It was said: It has a flavor. He said: And water has a flavor, but you rinse your mouth with it.”
Allah Almighty knows best.
Source: IslamQA