1. (Draught porter.) From pale malt, 31⁄2 q. s.; amber malt, 3 q. s.; brown malt, 11⁄2 q.; mash at twice with 28 and 24 barrels of water, boil with brown Kent hops, 56 lbs., and set with yeast, 40 lbs. Prod. 28 barrels, or 31⁄2 times the malt, besides 20 barrels of table-beer from a third mashing.
2. (Bottling porter; Brown stout.) From pale malt, 2 q. s.; amber and brown malt, of each 11⁄2 qr.; mash at 3 times with 12, 7, and 6 barrels of water, boil with hops, 50 lbs., and set with yeast, 26 lbs. Prod. 17 barrels, or 11⁄2 times the malt.
The purity and quality of porter, as well as of other malt liquors, may be inferred in the manner noticed under Beer; but can only be positively determined by a chemical examination.
For this purpose several distinct operations are required:—
1. Richness in ALCOHOL. This may be correctly found by the method of M. Gay-Lussac; or from the boiling point. (See Alcoholometry and Ebullioscope.) The method with anhydrous carbonate of potassa will also give results sufficiently near to the truth for ordinary purposes, when strong or old beer is operated on. The quantity of the liquor tested should be 3600 water grains measure; and it should be well agitated, with free exposure to the air, after weighing it, but before testing it for its alcohol. The weight of alcohol found, multiplied by 1·8587, gives its equivalent in sugar. This may be converted into ‘brewer’s pounds’ or density per barrel, as below.
2. Richness in SACCHARINE or EXTRACTIVE MATTER. A like quantity of the liquor under examination, after being boiled for some time to dissipate its alcohol, is made up with distilled water, so as to be again exactly equal to 3600 water-grains measure. The sp. gr. of the resulting liquid is then taken, and this is reduced to ‘brewers’ pounds’ per barrel, by multiplying its excess of density above that of water (or 1000) by 360, and pointing off the three right-hand figures as decimals.
3. Acetic acid or VINEGAR. This is determined by any of the common methods of ACIDIMETRY (which see; see also Acetimetry). Each grain of anhydrous acetic acid so found represents 1·6765 gr. of sugar.
4. Gravity of ORIGINAL WORT. This is obtained by the addition of the respective quantities of saccharine matter found in Nos. 1, 2, and 3 (above). These results are always slightly under the true original density of the wort, as cane sugar appears to have been taken by the Excise as the basis of their calculations. More correctly, 12% of proof spirit is equivalent to 19 lbs. of saccharine per barrel. 101⁄2 lbs. of saccharine are equiv. to 1 gall. of proof spirit.
5. Detection of NARCOTICS. This may be effected either by the method described under Alkaloid, or by one or other of the following processes:—
a. Half a gallon of the beer under examination is evaporated to dryness in a water bath; the resulting extract is boiled for 30 or 40 minutes in a covered vessel with 10 or 12 fl. oz. of alcohol or strong rectified spirit, the mixture being occasionally stirred with a glass rod, to promote the action of the menstruum; the alcoholic solution is next filtered, treated with a sufficient quantity of solution of diacetate of lead to precipitate colouring matter, and again filtered; the filtrate is treated with a few drops of dilute sulphuric acid, again filtered, and then evaporated to dryness; it may then be tested with any of the usual reagents, either in the solid state, or after being dissolved in distilled water. Or the extract, obtained as above, may be boiled as directed with rectified spirit, the