A lot of times I take a coffee and sip it slowly during the coming hours. During that period, if I eat a fruit, do I make a borei nefashos right after eating the fruit? If so, do I now have to make a new shehakol on the coffee?
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In general, the practice of drink a cup of coffee or sipping water over a few hours, is a practice that should be avoided, the reason being, that it will cause you to lose the chance to make a bracha achrona. The shiur to make a bracha achrona is usually until the food is digested, and for liquids it is much shorter than it is for foods. Therefore after half an hour after drinking, you cannot make a bracha achrona on the first liquid. Additionally, it is possible that you might have to make another bracha rishona. For this reason, the poskim say that when drinking liquids, one should make a bracha achrona right away, and when he wants to drink again, he will make another bracha rishona. Therefore in practicality your question will not really be applicable.
Biur Halacha 190-2 D:H Achar, Minchas Yitzchok 5-102 D:H Omnum, Kaf Hachayim O:Ch 184-29, Piskei Teshuvos 184- 11.