Possible Clues:

• Bitter in taste — harsh in tone
• Astringent
• Sharp, forthright
• Scathing
• Biting, as criticism
• Tasting sour or caustic in speech
• Best writing, perhaps, with Biro that's sharp
• Harsh and sharp in speech
• Bitter with pen under tree
• Bitter and sour maple with crumbs of biccy