The fasting person is expected to stay away from some acts in order for the ritual to be valid. When the so called prohibitions of the fast are violated, the fast will be void. Abstinence from food and sexual intimacy forms the essence of the fasting ritual, violating this rule would be violating the essence of fasting. Qadha (making up) and Kaffarah (expiation) are required whenever a rule is violated intentionally. Qadha is to make up for a fast the person broke before; kaffarah is a form of expiation and a way to atone for the broken fast. Among the forms of kaffarah for the Ramadan fast as mentioned in the practices of the Prophet are setting a slave free, fasting two months successively, if s/he is not capable, then s/he provides 60 Muslims a day's meal. (Halil Altuntaş, İsmail Karagöz, Oruç İlmihali, DİB. Yay, 2013, 100) However, only Qada is required for the one who violates a rule of fasting unintentionally. 

Detailed information about what necessitates Qadha and Kaffarah can be found in the books on the basics of Islam. 

Eating or drinking something out of forgetfulness, however, does not nullify the fast. The Prophet said that the one who accidentally eats or drinks something should continue their fast because Allah has given them a treat .(Bukhari, Sawm, 26)

Acts contrary to the meaning and purpose of the fast,  which might even break the fast if done excessively, are the makruh acts of fasting. Tasting or chewing, for example, are makruh because the possibility of swallowing it. Although it does not break the fast, treatments that weaken the body - like giving blood - are makruh while fasting. (Ilmihal, 406) The fasting person should avoid anything that could cause harm to the meaning of the fast.