If he can taste the food without it reaching the body cavity, it is permissible and does not break the fast, but it is disliked out of fear that it might reach his throat, as it says in the Tuhfa with the Minhaj, (3:425).
[s. It is not disliked for] one who needs to do it, such as a person who chews on some bread to soften it for a child, or someone who is trying to improve the food. It is not disliked for them to taste it, as the imams have stated. Refer to the Hashiya of Abd al-Hamid on the Tuhfa. (3:425)