Borer

From Halachipedia
  1. It is forbidden to separate on Shabbat by taking the refuse from the food. It is forbidden even when it’s done with one hand. [1]

References

  1. S”A 319:2 writes that it’s forbidden to take the refuse from food even with one hand. Mishna Brurah writes that even though some don’t have the words “one hand” in S”A, still one shouldn't be lenient to take to take refuse from food with one hand.