This section is from the book "Alcohol, Its Production, Properties, Chemistry, And Industrial Applications", by Charles Simmonds. Also available from Amazon: Alcohol: Its Production, Properties, Chemistry, And Industrial Applications.
In general terms, beer is a beverage which has been brewed, fermented, and bittered. Formerly, and typically, beer was brewed from malt, and bittered with hops ; but sugars and starchy substances other than malt are now commonly employed, and bitters other than hops are used to a small extent. In the United Kingdom, beer is legally "any liquor which is made or sold as a description of beer or as a substitute for beer, and which on analysis of a sample thereof at any time is found to contain more than two per cent. of proof spirit." It "includes ale, porter, spruce beer, black beer, and any other description of beer" (10 Edw. VII, c. 8, s. 52). A later enactment excludes from the legal definition of beer any" liquor made elsewhere than upon the licensed premises of a brewer for sale which on analysis of a sample thereof is found to be of an original gravity not exceeding 1016 degrees, and to contain not more than two per cent. of proof spirit" (5 Geo. V, c. 7, s. 8).
"Ale" was at one time distinct from beer, as not being bittered with hops, but the term has long been used indiscriminately with "beer" for the lighter-coloured varieties of malt liquors as distinct from stout, porter, and black beer.
At the present day, the lighter kinds of beer drunk in this country contain about (5 or 7 per cent. of proof spirit,1 and the original specific gravity of the wort before fermentation is usually about 1040 to 1043 (water = 1000). Ordinary dinner ale, pale ale, sonic makes of "porter," lager beer, and the beer generally supplied in public houses contains about 9 to 11 per cent. of proof spirit, and is of approximately 1050-1055 original gravity. Heavier beers and stout range from about 1060 to 1090 degrees of original gravity, and contain 11 to 14 per cent. of proof spirit; whilst special kinds of "strong ale" may be of more than 1100 original gravity, and contain up to 20 per cent. of proof spirit.
Chemically, beer consists of a weak spirituous solution of various sugars, acids, dextrins, proteins, flavouring and colouring matters; with a small quantity of mineral constituents, chiefly phosphates and sulphates.
On distillation, the volatile constituents are separated from the beer; these consist, apart from water, of alcohol, carbonic acid, acetic acid, and traces of minor constituents such as essential oils and higher fatty acids. The non-volatile constituents are usually referred to as the "extract" - more appropriately as the "residue."
The most frequent analytical operations required in the examination of beer are the determination of the proportion of alcohol and
1 This refers to normal circumstances, apart from war conditions. The milder kinds of "war" beer (1918) contained about 3 per cent. of proof spirit of the "original " specific gravity. In some cases, an estimation of the carbon dioxide, the acetic acid, the nitrogenous constituents, and the mineral ingredients, especially the chlorides, may be required; and occasionally search must be made for bitter substances other than hops, and for preservatives. The examination of the beer for saccharin is also of some importance, as the addition of this substance to beer is prohibited by law.
Original gravity. General considerations. - Beer in this country is not taxed upon the alcohol it contains; the basis of taxation is the specific gravity of the unfermented wort. Essentially, the wort of beer is a solution of maltodextrins and various sugars - maltose, dextrose, cane-sugar, and invert-sugar - either arising from the malt and grain used, or added as such. As soon as fermentation commences, the specific gravity begins to alter, and the finished beer is of lower density than the original wort, for two reasons. First, the destruction of sugar by fermentation removes solid matter from solution; and, secondly, the alcohol produced is specifically lighter than the wort. The original specific gravity of the unfermented wort can, however, be ascertained by the analysis of the partly-fermented wort, or of the finished beer, as the case may require.
As a first approximation, such an analysis might be based upon the well-known equations of Gay-Lussac denoting the conversion of sugar into alcohol. With maltose, for example: - C12H12O11+ H10 = 4C2H5OH + 4CO2; and it is readily calculable that 100 parts of this sugar yield theoretically 53'8 parts of alcohol. Hence by determining the quantity of alcohol in a given specimen of wort or beer we can find the equivalent amount of sugar destroyed; and from the known density of solutions of maltose we can thus deduce the corresponding loss of specific gravity. Also we can determine the actual specific gravity of the residual wort or beer freed from alcohol, and correcting this for the loss as above ascertained, we can, theoretically, obtain the original gravity of the wort.
In practice, however, this is not sufficiently accurate. A part of the sugar destroyed is not converted into alcohol. Moreover different sugars are present, and they do not all yield the same proportion of alcohol. Again, the introduction of yeast complicates the matter, since part of the solid matter of the wort is used up in sustaining the growth of the yeast, and a sensible quantity of alcohol may be added as such with the yeast itself. These and other disturbing factors, small individually, together influence the result sufficiently to render the figures given by the simple theoretical method as outlined above, only an approximation to what obtains in actual brewery operations.
We have, in fact, to fall back upon an empirical basis for the calculation of results sufficiently accurate to be used in practice. Starting with representative worts of known specific gravity, experimental fermentations have been carried out. From the examination of samples drawn as the operation proceeded, the actual loss of gravity consequent upon the production of known quantities of alcohol has been determined. The results have been embodied in statutory tables for use in assessing the duty on beer.