This is the 5922nd most frequent Japanese word.
もっぱら
"Exclusively; solely; primarily."
The word 'もっぱら' is used to show exclusivity or a focus on a single activity, i.e., 'exclusively or solely engaged in reading'.
彼はもっぱら読書にふける毎日を送っている。
He spends his days entirely absorbed in reading.
'もっぱら' emphasizes the singular focus on local ingredients, showing that they are exclusively dedicated to this practice.
このカフェではもっぱら地元の材料を使っている。
This café exclusively uses local ingredients.
In this context, 'もっぱら' indicates that the conversation was exclusively or entirely focused on hobbies.