The proportion of malt extract in beer can be directly determined by the evaporation of 5 or 10 c.c. of the sample in a capacious platinum dish over the water-bath and drying the residue until constant weight is obtained.[76] It should be allowed to cool under a bell-jar over calcium chloride, before weighing. Usually the estimation is made by an indirect process, which consists in removing the alcohol by evaporation, bringing the liquid up to its original volume by the addition of water, and then taking its specific gravity and determining the percentage of malt extract by means of the following table:—
Specific Gravity and Strength of Malt Extract.
| Specific Gravity. | Per Cent. Malt Extract. |
| 1·000 | 0·000 |
| 1·001 | 0·250 |
| 1·002 | 0·500 |
| 1·003 | 0·750 |
| 1·004 | 1·000 |
| 1·005 | 1·250 |
| 1·006 | 1·500 |
| 1·007 | 1·750 |
| 1·008 | 2·000 |
| 1·009 | 2·250 |
| 1·010 | 2·500 |
| 1·011 | 2·750 |
| 1·012 | 3·000 |
| 1·013 | 3·250 |
| 1·014 | 3·500 |
| 1·015 | 3·750 |
| 1·016 | 4·000 |
| 1·017 | 4·250 |
| 1·018 | 4·500 |
| 1·019 | 4·750 |
| 1·020 | 5·000 |
| 1·021 | 5·250 |
| 1·022 | 5·500 |
| 1·023 | 5·750 |
| 1·024 | 6·000 |
| 1·025 | 6·244 |
| 1·026 | 6·488 |
| 1·027 | 6·731 |
| 1·028 | 6·975 |
| 1·029 | 7·219 |
| 1·030 | 7·463 |
| 1·031 | 7·706 |
| 1·032 | 7·950 |
| 1·033 | 8·195 |
| 1·034 | 8·438 |
| 1·035 | 8·681 |
| 1·036 | 8·925 |
| 1·037 | 9·170 |
| 1·038 | 9·413 |
| 1·039 | 9·657 |
| 1·040 | 9·901 |
| 1·041 | 10·142 |
| 1·042 | 10·381 |
| 1·043 | 10·619 |
| 1·044 | 10·857 |
| 1·045 | 11·095 |
| 1·046 | 11·333 |
| 1·047 | 11·595 |
| 1·048 | 11·809 |
| 1·049 | 12·047 |
| 1·050 | 12·285 |
| 1·051 | 12·523 |
| 1·052 | 12·761 |
| 1·053 | 13·000 |
| 1·054 | 13·238 |
| 1·055 | 13·476 |
| 1·056 | 13·714 |
| 1·057 | 13·952 |
| 1·058 | 14·190 |
| 1·059 | 14·428 |
| 1·060 | 14·666 |
| 1·061 | 14·904 |
| 1·062 | 15·139 |
| 1·063 | 15·371 |
| 1·064 | 15·604 |
| 1·065 | 15·837 |
| 1·066 | 16·070 |
| 1·067 | 16·302 |
| 1·068 | 16·534 |
| 1·069 | 16·767 |
| 1·070 | 17·000 |
The sugar contained in beer is best determined by by taking 50 c.c. of the sample, adding 10 c.c. of plumbic basic acetate solution, and making the volume of the mixture up to 300 c.c. with distilled water. After standing for some time the solution is passed through a dry filter. It is then examined by cautiously adding it from a burette to 10 c.c. of Fehling’s solution (diluted with 40 c.c. of distilled water and brought to the boiling-point), until the blue colour of the latter disappears (see p. [111]). It should be borne in mind that, while 10 c.c. of Fehling’s solution are reduced by 0·05 gramme of glucose, it requires 0·075 gramme of maltose to effect the same reduction.
In order to estimate the dextrine, 10 c.c. of the beer are reduced by evaporation to about 4 c.c., and heated with 1 c.c. of dilute sulphuric acid to 110° by means of an oil-bath in a strong hermetically closed glass tube for five hours. At the completion of this operation the solution is neutralised with sodium hydroxide, diluted, and the total glucose determined by Fehling’s reagent, as just described. The glucose due to the conversion of the dextrine is found by deducting the amount of maltose (expressed in terms of glucose) previously obtained from the total glucose; 10 parts of glucose represent 9 parts of dextrine.
The organic acids (acetic and lactic) are estimated as follows:—(a) Acetic acid, by distilling 100 c.c. of the sample almost to dryness, and titrating the distillate with decinormal soda solution; (b) Lactic acid, by dissolving the residue remaining after the distillation in water, and either determining its acidity by decinormal soda, or by treating the residue with water and a little sulphuric acid, adding barium carbonate to the mixture, heating in the water-bath and filtering, the precipitate being thoroughly washed with hot water. The filtrate is then concentrated to a syrup by evaporation, and agitated in a test-tube with a mixture of 1 part each of sulphuric acid, alcohol, and water, and 10 parts of ether. After standing at rest for some time, the ethereal solution is separated by means of a pipette and evaporated to dryness in a tared capsule. The residue (impure lactic acid) can be weighed, or it is dissolved in water, the solution treated with zinc carbonate, and the lactic acid determined as zinc lactate, which contains 54·5 per cent. of the anhydrous acid.
Phosphoric acid may be estimated in the beer directly by first expelling the carbonic acid, then adding a small quantity of potassium acetate, heating, and titrating with a standard solution of uranium acetate, using potassium ferrocyanide as the indicator. It can also be determined gravimetrically in the ash.
The estimation of the ash is made by evaporating 100 c.c. of the sample in a weighed platinum dish to dryness, and incinerating the residue at a rather moderate heat, so as to avoid volatilisation of the chlorides. The amount of ash in normal beer should never exceed 0·5 per cent., the usual proportion being about 0·3 per cent.; this would naturally be increased by the addition of sodium bicarbonate or sodium chloride to the beer. The complete analysis of the ash is seldom necessary, but it is often of importance to estimate the amount of sodium chloride contained. This is effected by dissolving the ash-residue in distilled water and precipitating the chlorine from an aliquot portion of the solution by silver nitrate; one part of the precipitate obtained represents 0·409 part of common salt. The proportion of sodium chloride in pure beer is very inconsiderable, but it may be added to the beverage either to improve the flavour or to create thirst. For the determination of phosphoric acid, a weighed portion of the ash is dissolved in nitric acid, the solution evaporated to dryness, and the residue boiled with water containing a little nitric acid. It is then filtered, concentrated by evaporation, an excess of ammonium molybdate solution added, and the mixture set aside for about ten hours, after which the precipitate formed is separated by filtration and dissolved in ammonium hydroxide. A solution of magnesium sulphate (mixed with a considerable quantity of ammonium chloride) is now added, and the precipitated ammonio-magnesium phosphate collected, washed, ignited, and weighed, 100 parts of this precipitate contain 64 parts of phosphoric anhydride (P2O5).
The positive detection of the presence of artificial substitutes for malt in beer is a matter of considerable difficulty. According to Haarstick, a large proportion of commercial glucose contains a substance termed amylin, which exerts a strong dextro-rotary effect upon polarised light, but is not destroyed by fermentation, and upon these facts is based a process for the identification of starch-sugar in beer. It is executed by evaporating 1 litre of the sample to the consistency of a syrup and separating the dextrine present by the gradual addition of 95 per cent. alcohol.[77] After standing at rest for several hours the liquid is filtered, the greater portion of the alcohol removed from the filtrate by distillation, and the residual fluid evaporated to dryness over the water-bath. The solid residue is then diluted to about a litre, yeast added, and the sugar present decomposed by allowing fermentation to take place for three or four days, at a temperature of 20°. It was found that, under these conditions, pure beer afforded a solution which was optically inactive when examined by the polariscope, while beer prepared from artificial glucose gave a solution possessing decided dextro-rotary power. The use of rice and glucose in the manufacture of beer is also indicated when there is a deficiency in the proportion of phosphoric acid in the ash, and of the extract, which applies, although to a somewhat less extent, if wheat or corn meal has been substituted for barley malt.
The following conclusions were reached by a commission of chemists appointed in Germany to determine standards for beer:—A fixed relation between the quantity of alcohol and extract in beer does not invariably exist. As a rule in Bavarian and lager beer, for 1 part by weight of alcohol a maximum of 2 parts and a minimum of 1·5 parts of extract should be present. In case malt has been replaced by glucose, or other non-nitrogenous substances, the percentage of nitrogen in the extract will fall below 0·65. The acidity should not exceed 3 c.c. of normal alkali solution for 100 c.c. of beer. The ash should not exceed 0·3 per cent. The maximum proportion of glycerine should not exceed 0·25 per cent. For clarification, the following means are permissible: Filtration, the use of shavings, etc., and of isinglass or other forms of gelatine; for preservation, carbonic acid gas, and salicylic acid may be employed—the latter, however, only in beer which is intended for exportation to countries where its use is not prohibited.