Bitterness in beer - Bitter acids
12 important questions on Bitterness in beer - Bitter acids
Where does the bitter taste in beer originate from?
Which 2 types of bitter acids exist?
- Alpha-acids (humulones)
- Beta-acids (lupulones)
How do alpha and beta-acids look?
- They contain a central 6-membered carbon ring
- Prenyl chains
- R-groups varying in length
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What is the difference between alpha- and beta-acids?
- B-acids have an additional prenyl chain. It makes the molecule more hydrophobic, which influences the water-solubility of the beta-acids.
- They are more apolar than the alpha-acids, and consequently have a lower water-solubility. Alpha-acids are reasonably water-soluble, but the beta-acids are not.
Are there a lot of beta-acids in hops?
Are alpha- and beta-acids bitter?
What happens during heating in beer?
- The Oktoberfest Umlagerung.
- The 6-membered ring of the alpha-acids is converted to a 5-membered ring, via ring-contraction and rearrangement of the prenyl chain. Iso-alpha-acids are formed.
Why are bitter acids organic acids?
- Normally organic acids contain a carboxyl group. The bitter acids lack this group
- The acidic character of bitter acids (alpha, iso-alpha and beta) is induced by their keto-enol-tautomerism.
- The hydrogen atom is easily released and can relocate over the molecule, making it the acidic hydrogen.
What is the pKa of iso-alpha-acids?
When are trans- and cis-iso-alpha-acids formed?
Which bitter acids have a lingering effect?
- Iso-alpha-acids --> both cis and trans show lingering effect, as the fluorescence fades quickly
- Alpha- and beta-acids --> stronger lingering effect. Hints at a stronger bitter response.
Which receptors respond to the bitter acids of beer?
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