Our Sages teach us (Eruvin 40b) that one should recite the “Shehecheyanu” blessing upon seeing a new fruit that renews once a year. Even if one sees this fruit in the hands of another person or on the tree, one should recite the “Shehecheyanu” blessing.
Nevertheless, the Poskim and Maran Ha’Shulchan Aruch (Chapter 225) write that nowadays, one should only recite the “Shehecheyanu” blessing only upon eating the new fruit. The Poskim discuss several reasons for why one should recite this blessing specifically when eating the fruit as opposed to when one sees it. The Magen Avraham writes that the reason for this is based on the Rishonim (Sefer Mitzvot Katan and others) who write that when one sees a new fruit and plans on eating it at a later time, one should only recite the “Shehecheyanu” blessing when eating the fruit, for the primary enjoyment of the fruit is when one eats it. Thus, it has become customary to always recite this blessing when eating the fruit.
Nevertheless, if one did recite the “Shehecheyanu” blessing upon seeing the fruit for whatever reason, one should not repeat this blessing when one eats the fruit, for the individual is exempted by the blessing he recited at the time he saw it. However, it is improper to deviate from the prevalent custom established by the great Poskim and quoted in Shulchan Aruch which is to only recite this blessing when eating the fruit.
In any case, we see that the primary establishment of the “Shehecheyanu” blessing is for the enjoyment one has from the fruit, either when seeing it or eating it. Thus, if one does not derive any enjoyment from the fruit, such as, if one was served a new fruit and one does not particularly like this fruit and only wants to taste the fruit to see how it tastes or if the fruit is not yet ripe enough and it is bitter or sour, one should not recite the “Shehecheyanu” blessing upon eating the fruit. Indeed, Hagaon Harav Shmuel Ha’Levi Wosner zt”l rules likewise (in his Responsa Shevet Ha’Levi, Volume 4, Chapter 25) that if one knows that one is not glad as a result of the fruit, one should not recite the “Shehecheyanu” blessing. The Sefer Halacha Berura (Chapter 225) quotes his opinion as Halacha.
Similarly, since the primary enactment of the blessing was for seeing the new fruit and the enjoyment this engenders, clearly, even if one eats only a small amount of the fruit, one may still recite the “Shehecheyanu” blessing since one is happy and enjoys the new fruit.