I'll be honest with you. Much of this goes right over my head. I can only really understand the first four rows of the analysis.
By A. D. Rudin, B.Sc.. and M. J. Watts. B.Sc (Ind Coope, ltd., Burton-on-Trent)
Received 19th May. 1961
Spectrophotometry studies on the isooctane extracts obtained in various common methods for determining bitterness revealed that an ale brewed in 1875 now contains an unusually large proportion of materials other than isohumulones. A similar result obtained for modern ales maintained for short periods at elevated temperatures in contact with air suggests that these "background" materials may have been formed from isohumulones by oxidation. Other constituents in the old ale are consistent with its high original gravity and its age.
A SAMPLE of ale brewed in 1875 for the Arctic Expedition Jed by Capt. Nares has recently been examined and the results Table I) have certain interesting features. Thus, it was found that very different values, ranging from 50 down to 11 p.p.m. for the bitterness content of the beer, were
TABLE 1Analysis of an Ale Brewed is 1875
Present gravity 1053.4º Original gravity 1126.4º Alcohol (v/v) 9.65% Colour (E.B.C.) 156º Nitrogen (mg. per 100 ml.) 200.3 pH 3.9 Esters (as ethyl acetate, p.p.m.) 77 Fusel oils (p.p.m.) 110 Aldehydes (as acetaldehyde. p.p.m.) 15 Isohumulone (Klopper,2 p.p.m.) 50 (Rigby & Bethune.3 method I. p.p.m.) 50 (Rigby & Betbune,method II; p.p.m.) 11 Dextrin 6.95% Maltotriose 2.15% Maltose 2.30% Hexose 1.70%
obtained using three of the common methods of analysis based on spectroscopic measurement. Detailed examination of the absorption spectra of the various solutions obtained during these analyses showed that they generally differed markedly compared with corresponding solutions prepared from Infers brewed nowadays. Thus, the solution obtained by extracting acidified beer with iwetane (Klopper2) absorbed strongly at ?88-270 mμ. and not, as is more usual, at ?75 mμ. (Fig. 1; Curve I). Washing the extract with acidified methanol did not appreciable alter the position of the maximum absorption as would be expected if this treatment had completely removed "background material," i.e., substances other than isohumulones (curve II). Similarly, the absorption spectrum of the unwashed tsooctanc after dilution with alkaline methanol (Rigby & Bethune,3 method I) failed to show the normal well defined absorption maximum at 255 mμ. (curve III) although the washed isooctane on similar treatment (Rigby & Bethune3 method II) had an absorption spectrum strongly reminiscent of that obtained using alkaline solutions of pure isohumulones (curve IV).
In computing bitterness contents from the results obtained using Klopper's method or Rigby & Bethune's "method I," an allowance, approximating in both cases to one-third of the measured absorbence, is made for materials present in the extract which are not isohumulones. In Rigby & Bethune's method II no such allowance is made, as these background substances are presumed to have been removed by the washing of the isooctane extract with acidified methanol. On the basis of the result obtained by this latter method, which is generally considered to give a reliable measure of true isohmnulones, the normal allowance made for "background" method in the two other methods is clearly too small in the present case.
The above facts suggest, therefore, that this ale now contains little true isohumulone although a much higher original value is probable in view of the larger concentrations of hops used in brewing 86 years ago. In connection with this presumed decrease in isohumulone content, it has been shown that modern strong ales maintained at 50º C. in the presence of air soon show appreciable
Fig. 1 - Absorption spectra of various solutions obtained m the analysis of bitterness of beers. (I) isooctane extract of acidified beer; (II) isooctane extract washed with acidified methanol; (III) isooctane extract diluted with alkaline methanol; (IV) washed isooctane extract, diluted with alkaline methanol.
changes in their bittering content. Thus, within 7 days the isohumulone content as measured by Klopper's method decreased by 30% while using Rigby & Bethune's method II a more striking decrease of about 50% was observed. Furthermore, the absorption spectra of the extracts from the modern ale after treatment showed some of the features noted in the old ale, e.g., the absorption peak of the isooctane extract shifted from 275 to 267 mμ. It may well be, therefore, that over the years the bitter substances originally present in the 1875 ale have undergone modification similar to that induced rapidly in its modern equivalent by maintaining it under the conditions described. Furthermore, it seems likely that oxidation may have played an important part in these transformations.
Regarding other constituents, appreciable quantities of fermentable sugars including glucose, maltose and maltotriose were detected, but there was only a slight trace of fructose and no sucrose. The dark colour of the ale was strongly adsorbed on nylon and prevented, an accurate determination of anthocyanogens. Compared with present-day beers neither the aldehyde nor the fusel-oil content of this old ale seems exceptional, whereas its content of esters is rather high and this fact is reflected in its vinous odour and taste. The ale was still sound and bright but adhering strongly to the inside of the bottle (champagne-type of green glass holding 1 quart) was a brown, mainly proteinaceous, deposit in which were detected a few badly distorted yeast cells, none of which appeared to contain spores; no viable organisms could be detected in the beer itself.
It is interesting to note that in 1928 Hopkins, examining a strong ale of similar vintage (1879), observed mis-shapen yeast cells in the sediment and some of these contained spores which appeared to be viable. Incidentally, his sample had a high ester content (330 p.p.m.) and a low pH value (3.60).
Acknowledgement. —The authors wish to thank the Chairman and Directors of Ind Coope, Ltd., for permission to publish these results.
1. Hopkins, R. H., this Journal 1928, 403.
2. Klopper. W. J., Brauwissenschaft, 1955, 101.
3. Rigby, F. L., & Bethune, J. L., this Journal, 1955, 325."
The Brewer, volume 67, 1961, pages 511 - 513.
What they seem to be saying is that all the bittereness Iisohumulone) has disappeared. And that you can see a substantial drop in isohumulone level if you leave a beer at 50º C and exposed to air.
The colour value looks about right. The Arctic Ale we tried I would guess was somewhere around 150º EBC.
A pH value of 3.9 makes the beer quite acidic. I can't say the one we tried came over as particularly sour. Then again, with all the other stuff going on, it might not have been that noticeable. The wine-like flavour mentioned certainly does match my subjective perception of the beer.