Organoleptic Trials With Hop Bitter Substances

Abstract

Pure hops-derived substances were added to unhopped beer. Illumination only produced a sun-struck flavour with cfs-isohumulone, trans-isohumulone and racemic trans-isohumulone. It seems that 3-methyl-butenyl-mercaptan is not or not alone responsible for sun-struck flavour.Tests trials show that trans-isohumulone, cis-tsohumulone, racemic trans-iso humulone, trans-pt-isohumulone and ds-^-isohumulone do not show significant differences in bitter taste and bittering power. Fresh solutions of these bitter acids are not as bitter as solutions which have been kept for a few weeks.Since it is known that the isomerization of compounds in question is not easy as only humulone produces two diastereo-isomers,6toms-isohumulone is crystalline with in.p. namely trans-and cts-isohumulone,* the 08°C. and can thus be purified completely question of their relative bitterness is clearly by recrystallization. The cts-isohumulone important. The interesting point behind is an oil and even the most careful work this is obviously that if one of the two isocannot produce it completely pure. It mers is more bitter, industrial isomerization cannot be distilled without decomposition conditions could be adapted to produce more and partition procedures like chromatoof the more bitter iso-a-acid. graphy or countercurrent distribution, alOver a very wide range of pH, aqueous though producing highly purified material, alkaline isomerization gives the same equilido not yield completely pure substances, brium mixture with a ratio 65-70/30-35 for Indeed, these procedures yield the desired the cts-and /rans-isomers.' Magnesium catasubstance in dilute solution and the evaporalysed isomerization, however, produces a tion of the large excess of solvent always 50-50 mixture.4Photo-isomerization* in leaves some impurities behind. Also, it is methanol leads to a high percentage of the very difficult to remove the last traces of frans-isomer.solvent from an oil like cts-isohumulone. A comparison of bitterness for the two These observations are general for the field • Trans-and ei's-isohumulone are new names for isohumulonc A and D respectively according to the nomenclature proposals ol the Hops Liaison Committee of the E.B.C.

Relationships of Sensory Bitterness in Lager Beers to Iso-α-Acid Contents

“…It has been proposed that iso-␣-acids are the most important source of bitterness in beers 10,24 . Lager 16, with the lowest iso-␣-acids, had the highest total content of tetrahydroiso-␣-acids of all the products.…”

“…These compounds exist as the equally bitter cis-and trans-isomers. Iso-␣-acids are thought responsible for 70% of observed sensory bitterness 23,24 . In beer, trans-iso-␣-acids are less stable then cis-iso-␣ acids during aging 4 due to their lower aqueous solubility 3 ; ␤-acids are believed to contribute little to the bitterness perception in comparison with ␣-acids.…”

“…Despite many misconceptions, bitterness receptors are currently thought to be located on papillae concentrated on the back of the upper surface of the tongue and additionally there are also likely sensors on the posterior of the soft palate 17 . There are a number of studies on bitterness in beer 8,10,12,14,23,24 and iso-␣-acid concentrations have been correlated with bitterness intensity 10,12 . In time-intensity profiling, King and Moreau 14 showed that maximum intensity was reached on first ingestion, and reduced for subsequent ingestions.…”

Sensory Characterization of Commercial Lager Beers and Their Correlations with Iso-α-Acid Concentrations

“…The intensity of bitterness has been related to the concentration of iso-α-acids [24,27,28,31,32]and to a lesser extent with the alcohol content in beer [33]. In particular, the iso-α-acids are responsible for approximately 70% of the bitterness of beer [34,35,36,37]. It is generally recognised that the main bittering principles of beer are the hop-derived iso-α-acids [38].…”

On the Sunstruck Flavour of Beer

“…Furthermore the photolysis occurs with light of a rather long wavelength (day light) and exclusively with iso-a-acids. 3 The reasons for this are not obvious. The result of our efforts however indicate that only 3-methyl-2-butene-l-thiol was formed and therefore the results of the Japanese research group have been confirmed.…”