Page:A Practical Treatise on Brewing (4th ed.).djvu/121

Rh often extends over the tun. This almost invariably happens where there is any galvanic action from chains of pipes, or a mixture of metals; and cannot be cured or prevented, but by doing away with the cause: that is by insulating the tuns.

4. After a time, the light yeasty head should drop a little, perhaps 3 or 4 inches. This we call the 4th change. The aroma should now be very vinous and pungent.

5. The light yeasty head which had dropped, should now rise to what we call a close yeasty head, having the appearance of yeast all over, with many little air bubbles on the top, not, however, larger than a nut or a walnut; these constantly breaking, and others supplying their place. If the fermentation has been healthy throughout, the close yeasty head will continue rising, and puffing out gas from the air bells, until the beer is thought ready for cleansing. This will take place earlier or later, according to the quality of the beer and the public taste. Should all these changes, as before stated, take place regularly, and be accompanied through the process by a sound healthy aroma, (generally termed "stomach,") we may rest assured that all is right, and that the beer, if afterwards properly treated in storing, will turn out sound and good. Sometimes, however, instead of these five changes, not more than three are perceptible, all of them fretful and unhealthy. (These appearances will be