Page:A Practical Treatise on Brewing (4th ed.).djvu/125

Rh In the early part of our practice we have had occasion to see a good many boiling fermentations which we could not then account for. Since that time, however, we have been enabled to trace the causes, and invariably to remove them.

Many think that fermentation goes on better when the gyle-tuns are accurately closed, so as to prevent contact with the atmosphere. In as far as regards the atmosphere, this opinion is correct; but when fermentation goes on vigorously, there can be no connection with the atmosphere,—the great production of carbonic acid gas excluding it. Carbonic acid gas is heavier than atmospheric air, in the proportion of 1527 to 1000, and while it ﬂoats on the surface of the beer, and at the same time is produced in such quantities as to be constantly making its escape, atmospheric air cannot possibly interfere.

About the year 1824, Mr. Gray, of Westham, on Madame Gervas’s principle, attempted to introduce close fermentations into this country. It was tried in several places, but we have never heard of its having been permanently adopted. What may be denominated close fermentations are however, still practised in many parts of the country. When the worts are gathered together in the tun, a certain portion of yeast is added; the gyle-tuns are then