Context: Hops contain several characteristics that brewers desire in beer. Hops contribute a bitterness that balances the sweetness of the malt; the bitterness of beers is measured on the International Bitterness Units scale. Hops contribute floral, citrus, and herbal aromas and flavours to beer. Hops 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.

Question: What is the main cause for the bitterness in beer?
Answer: Hops

Question: What is the main goals for the sweetness of beer?
Answer: malt

Question: How is the bitterness in most beers generally measured?
Answer: the International Bitterness Units scale

Question: The acidity of what ingredient acts as a preservative in beer?
Answer: hops

Question: What do you call the length of time that foam is on top of beer because of carbonation?
Answer: head retention

Question: What does beer contain that brewers desire in hops?
Answer: Unanswerable

Question: What is measured by the Bitterness International Units scale?
Answer: Unanswerable

Question: What is retention head?
Answer: Unanswerable

Question: What type of effect do floral hops have?
Answer: Unanswerable