Tasting Food During a Fast
Question
I am cooking in an institution for children and I am fasting today (Fast of Gedaliah), am I allowed to taste the food?
Answer
According to the Rema, it is forbidden to taste the food even if you spit it out afterward, and this is the custom of the Ashkenazim. According to the Mechaber, it is permitted to taste less than the measure of a revi'it if you spit out the food and do not swallow after tasting.
The poskim are divided regarding the opinion of the Shulchan Aruch on whether the permitted tasting is only up to the measure of a revi'it cumulatively throughout the day, or if it is allowed to taste several times during the day, with each tasting being less than a revi'it, and the Mishnah Berurah rules to be stringent.
Source
Shulchan Aruch, Siman 567, Se'if 1. Mishnah Berurah, Se'if Katan 7.