Page:A Practical Treatise on Brewing (4th ed.).djvu/95

Rh the gravities in the gyle-tun, making allowance only for What may be retained by the hops in the last wort.

We all know that the gravities of the taps, or worts running from the mash-tun, vary considerably, according to the times at which the samples may be taken; thus leading to erroneous conclusions. The only accurate mode, therefore, of calculating the gravities of the unboiled worts, must be by taking samples from the under-back after being thoroughly roused, or better, from the copper when the worts are therein collected, and after about ten minutes’ boiling.

The common practice is even then to calculate the gravity as when reduced to a temperature of 60°, without making any deduction for the decrease in quantity necessary to reduce the worts to that temperature, by evaporation and condensation. We thus calculate a gravity (taking in what is retained by the hops) of at least ten per cent. more than we actually have: making all the difference between the (so denominated) raw and boiled gravities.

The Excise, when taking the dip of hot worts in the coolers, always allowed ten per cent. for evaporation and condensation. The same allowance should be made when taking hot worts in the copper—when we shall find that the raw and boiled gravities will very nearly correspond.