Lemon slices have a sour taste over time, so it is better to remove them when they become the taste you want. I prefer to use lemon peel because it tastes better to feel the scent of the peel than the lemon sourness in the coffee taste. If you have plain-flavored coffee beans, you can experience living with delicious beans. The lemon peel can be cut into appropriate sizes with a fruit knife or potato knife.