Squeezing the bag of grain and tannins are not synonymous. Excerpted and paraphrased from the books “Water - A Comprehensive Guide for Brewers” and “Malt - A Practical Guide From Field to Brewhouse” - Tannins, a subset of polyphenols, are present in grain husks and cell walls. They are released at mash temps and bind with proteins to form haze. In conjunction with a pH above 6, excess tannins are extracted and impart an astringent flavor - they can not be produced by pressure.
