Possible Clues:

• Sourness
• Bitterness
• Harshness or sharpness of speech
• A European loses the head in Paris, for instance, out of bitterness, in a manner of speaking
• Travelling by air, etc., out of bitterness, in a manner of speaking
• One really gutted about taste — that's sourness
• Tree, by squeezing it, produces vitriol
• Sharp and forthright manner
• When rattled, I react by showing bitterness
• Tartness of tone