First, let's look at the primary fermentation:
This stuff about different fermentation temperatures for Mild Ale and Old Ale is new to me. What I've seen in brewing records (admittedly a couple of decades later than this text) is that while different strengths of Ale were pitched at different temperatures, the maximum temperature achieved was pretty constant. Stronger worts were pitched cooler because they would generate more heat.
As in this part of the process the greatest effects are produced by the heat of the fermentation, so the greatest attention to its progress is necessary. The first heat (that is, when all the wort is first in the gyle tun) is to be considered of no other consequence than as conducing to the last or highest heat to which the fermentation will arrive; and this is found to have a very important influence on the flavour and other qualities of the ale. At 75° the first flavour of mild ale commences; for under that it is more properly the flavour of ale intended to be improved by long keeping. At 80° the flavour of ale is more perfect; at 85° it approaches the high flavour; at 90° it may be termed high, but is sometimes carried to 100° and upwards; the flavour increasing as the heat of the fermentation rises. It must still be remembered that I refer to the highest heat; and therefore at whatever degree you would have the fermentation finish, you must begin it at such a heat as experience has taught you will rise at last to the desired heat, but no higher. For instance, a wort of thirty pounds per barrel ought to increase about 15°, so that in order to arrive at 80°, you. must begin at 65°; but as it is impossible to say how your yeast will ferment (upon the quality of which the success of this operation entirely depends), it were safer in a small gyle, and in a low heat of the atmosphere, to begin at first between 65° and 70°; and if you find it increase 15° or more, you are to lower the heat of your next gyle accordingly;that is, so as to bring your highest heat of fermentation between 75° and 80°, or not much to exceed the latter; for, though a high heat produces the most agreeable flavour, the ale will not ultimately be so lively, nor will it be so soon fine, as from a contrary practice. It may not, however, be amiss to remark, that Forlow's celebrated Cambridge ale was begun at the heat of 90°, and has been sometimes carried as high as near 110°, producing that peculiarity of flavour which rendered his and the ale at one of the colleges by the same man, so famous, that some of it has been drunk at the king's table.
The quantity of good solid yeast to be used, should be proportioned to the specific gravity of the worts, the prevailing heat of the weather, and the heat of fermentation. To a wort of thirty pounds per barrel, if the heat of the air be low, and the first heat of fermentation 65°, or a little more, two pounds per barrel, or more, may be used. If the first heat be 70°, or not much under, 1.5, or 1.75 lbs. maybe sufficient. This, when the first heat is about 70°, may be all used at first; when it is lower, two-thirds may be used at first, and the remainder the next morning. In either case the quantity first used should be put into the gyle-tun, and as much wort let down to it as will cover the bottom, one and a half or two inches. The heat of this wort should not be less than 85° or 90°, in which state, being well mixed with the yeast, it puts it into immediate action, and prepares it for the reception of the rest of the wort at the required heat. When an addition of yeast is made, the whole should be well roused, to mix them the more readily.
These previous steps being taken, there is nothing uncertain but the strength and consequent operation of the yeast; and if the heat of the fermentation fall considerably short of the increase before-mentioned, the whole fermentation will be imperfect, the ale will have a heavy mixed flavour of sweet and bitter, and the fault is to be attributed to nothing but want of strength in the yeast. This can only be remedied by a fresh supply from some other brewer; and you must not be disheartened if the first or second change should not succeed; for there must be a new supply procured till some be found which will answer the desired end.
Even when a perfect fermentation is procured, the strength of the yeast will in time degenerate, and render another change necessary; and particularly so when the fermentation is carried to its utmost extent.
It is also to be remembered that I do not recommend rousing the worts in the gyle-tun, except as before-mentioned, because it communicates a rank flavour of yeast to the ale, though it perhaps adds to its strength: this rule, however, can only hold good when the yeast is of sufficient strength ; for, when it is weak, or suspected of being so, it will be necessary not only to increase the yeast considerably, by additions at every three or four hours during the day after brewing, but to rouse, at every addition, and even to continue these rousings till cleansing, in order to carry off the saccharine of the malt, and produce, as much as possible, that uniformity of flavour which good yeast would have effected in the first instance."
"The art of brewing" by David Booth, 1829, pages 40 - 42. (Copy of text from Richardson's "Philosophical Principles of the Science of Brewing." 1798.)
Richardson claims that Mild Ale should be fermented at between 75º and 85º F to get the right flavour, with 80º F being the sweet spot. Whitbread in the 1830's fermented their Ales cooler than that. They pitched at 59º to 64º F and let the temperature rise to a maximum of 74º to 78º F. It was a similar story at Truman during the 1830's: pitching at 59º to 67º F, maximum temperature 70º to 79º F. Nowhere near the 90º or 100º F Richardson mentions.
As for the quantity of yeast, Whitbread (in the 1830's) varied the amount used much more than Richardson suggests. The stronger the wort, the more yeast pitched: 0.66 lbs per barrel for X Ale, 1.33 lbs for XX, 1.5 lbs for XXX and 2.5 lbs for XXXX.
Onwards to cleansing:
The length of the section discussing cleansing - considerable more than is dedicated to mashing, boiling or fermentation - shows how important the process was considered. It's basically the removal of most of the yeast. All sorts of methods and devices were used to cleanse beer, the most sophisticated being Burton unions.
It is my practice to look every two hours into the gyle-tun, during the fermentation, whence I observe its progress very accurately. My principal attention is directed to the heat of the fermentation, which generally increases very slowly at first, but when the fermentation is in full force, its general increase is half a degree per hour, which progress declines in proportion as the fermentation advances towards a conclusion, till at length it stands still, and sometimes decreases before the vinous fermentation is entirely complete, especially where the volume of wort is small. This, then, is the grand rule for cleansing: whilst the heat is increasing, you may rest assured that the vinous fermentation is not finished; but so soon as it is at its height, you are to turn your attention to the smell of the ale. Whence you will observe, that in the middle of the fermentation, the fixed air strikes into the head so powerfully, on smelling with the nose lower than the upper edge of the gyle-tun, that it would, perhaps, be death to inhale it a second time, without intermission; but this force so much abates towards the conclusion of the fermentation, that, at the proper period for cleansing, it no longer stings the nostrils, nor strikes violently into the head, but just feels warm, and being drawn into the lungs, only occasions strong efforts to discharge the gas exactly similar to the effect of a sudden exertion in running up a hill, vulgarly termed being out of breath. The ale will then have lost its saccharine if the fermentation has been perfect, and will have acquired an uniform vinosity both in its smell and taste. The head will also then have a regular compact appearance of yeast, provided it be so low a heat of fermentation as 75° or a little more, but in proportion as the heat is carried further, the head becomes less; so that a fermentation of 90° or more will only exhibit blistery bubbles, and discharge no yeast till the ale be cleansed into casks, which, in that case, should not be larger than barrels, because it requires the heat to be lessened as expeditiously as may be, to facilitate the discharge of the yeast, and larger casks would be apt to retain it too long.
It is an advisable practice, when the fermentation is carried to its utmost period, to use about seven pounds of flour from either wheat or beans, to a gyle of 25 to 30 barrels, at the time of cleansing, in order to accelerate the discharge of the yeast by the introduction of an extra portion of gas into the ale for that purpose. This should be whisked up in a pail, with some of the ale, till all the lumps are broken, when it may be enlarged to any specific quantity, and then having a portion poured into each cask, agreeably to its size, the ale is to be cleansed upon it.
Though the above rules for cleansing are entirely consistent with my system, I nevertheless have found it convenient to deviate from them, by cleansing at an earlier period, even while the heat of fermentation is yet increasing, and the fixed air is somewhat strong, in order to obtain a better producer of yeast, and thence to have less sediment in the casks, which sometimes subsides with difficulty after removal. By early cleansing, too, the yeast is preserved longer in a state proper for a perfect fermentation, than by a contrary practice. At any rate, however, there must be no saccharine taste perceptible at the time of deciding upon cleansing. When the cleaning is finished, the casks should be filled quite full, and be filled up out of the stillions every two or three hours during the first day, and three or four times the next When the ale has nearly done its fermentation, if that from the stillions does not run clear, a cask should be tapped, to fill up with, and that which is thick should be returned into the next gyle just before cleansing.
If the ale be racked off from its lees, about three or four days from cleansing, and you add to every barrel three pints or two quarts of hops, after having boiled in the first wort, and (when the heat of the air is low) whilst they are warm, it will contribute much to the liveliness and purity of the ale, and render it much less liable to disorder, in removing from cellar to cellar; but it is to be observed, that the hops thus added give some rankness to the flavour, and racking is not favourable to the preservation of the ale. In this practice the casks should be filled quite full, and bunged down close, venting only if the cask be in danger. But if the ale be not cracked, the casks should not be bunged down so long as the head of the ale can be kept up by repeated fillings; for otherwise there would be a circle of yeast formed round the inside of the bunghole, which would be in part washed off amongst the ale on removal, and tend to make it foul."
"The art of brewing" by David Booth, 1829, pages 42 - 43. (Copy of text from Richardson's "Philosophical Principles of the Science of Brewing." 1798.)
When's the right time to cleanse? When you don't risk suffocation by sticking your head into the fermenting vessel. I think I'd prefer to judge it by the state of the head. Seems a much safer method.
Adding flour to aid clarification. I've come across this one before. Isn't it the enzymes in the flour that create the effect? I seem to remember reading that.
Adding wet, warm, boiled hops is pretty different from modern dry hopping. It clearly isn't going to add any hop aroma. Quite what the point of the practice is, when Richardson admits that it gives "some rankness to the flavour" of the beer.