The Halacha states that a Beracha of Shehakol recited on a beverage will continue to exempt the drinking of that beverage throughout the day. For example, if a person is sitting in the Bet Midrash with a cup of coffee or tea, sipping the drink as he learns, occasionally refilling his cup, the one Beracha of Shehakol recited in the morning will cover the drinking of the entire day.
The Poskim discuss whether this is true even if he waits "the time of digestion"-i.e. 72 minutes (or 90 minutes) in between drinks. Does such a hiatus sever the connection to the original Beracha, or is the Shehakol still "alive"?
The Magen Abraham (Rav Abraham Gombiner, Poland, 1637-1682) rules that the original Beracha has expired, and he must make a new Beracha. The Kaf HaHayim testified that this was the custom in the Yeshivat Mekubalim Bet El.
On the other hand, other Poskim such as the Ginat Vradim and the Erech Hashulhan disagree. They hold that the time lapse does not nullify the original Beracha, as long as the person did not mentally decide to stop drinking. The Saba Kadisha Alfandari concurred with this position and argued that the fact that the practice in Yeshivat Bet El was different does not mean that this is the conclusive Halacha. There is at least a "Safek Beracha"-uncertainty in the Halacha, which is resolved by not saying a new Beracha.
The custom used to be that during a Ta’anit Dibur, in which the Tehilim is recited three times, the Shamash would bring coffee before beginning chapter 119, which is the longest chapter. After drinking the coffee, they would continue saying Tehilim until, two hours later, they would reach chapter 119 again. According to the Magen Abraham, they would need to recite a new Beracha on the second round of coffee, whereas, according to the Saba Kadisha, they would not.
Hacham Ovadia rules in accordance with the Saba Kadisha that one should not make a new Shehakol if a long time elapsed, since it is a Safek Berachot. Rabbi Bittan suggests avoiding this uncertainty by leaving the building briefly before the next cup. This generates a Shinui Makom and requires a new Shehakol according to all opinions. This is not considered making a "Beracha She’enah Sriha"-unnecessary Beracha- since it is done for the legitimate purpose of alleviating a Halachic doubt. Alternatively, one can employ "Negative Kavana" and explicitly intend that the original Shehakol only exempt the first cup. In that case, he would need to make a new Beracha on a second cup, even before an hour and a half.
The original Beracha of Shehakol remains in effect, even if a long time elapsed between drinks, and no new Beracha is needed.