Sugar will make it much sweeter, you know.
It's another verb with the kanji 増! This one means to increase too! But! These are unconscious increases, whereas 増やす are usually for conscious increases.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You haven't learned this reading yet so here's a mnemonic to help you:
What increases with time? Your love for your mama (ま)! Your love for her will grow and grow the older you get! I love you, mama!