Alcohol denatures a protein mainly by disrupting the intramolecular hydrogen bonding between the side chains, which is essential to maintain the tertiary protein structure. The alcohol molecules compete with the amino acid residues to participate in forming new hydrogen bonds, which distances the side chains from each other and thus breaks protein’s tertiary structure. Besides, some alcohols can also interact with the hydrophobic residues in a protein, destroying its hydrophobic core and resulting in denaturation.