<answer>Hops</answer> contain several characteristics that brewers desire in beer. <answer>Hops</answer> contribute a bitterness that balances the sweetness of the malt; the bitterness of beers is measured on the International Bitterness Units scale. <answer>Hops</answer> contribute floral, citrus, and herbal aromas and flavours to beer. <answer>Hops</answer> have an antibiotic effect that favours the activity of brewer's yeast over less desirable microorganisms and aids in "head retention", the length of time that a foamy head created by carbonation will last. The acidity of hops is a preservative.
What is the main cause for the bitterness in beer?
Hops