In and about the city of London, the most intense cold that has been observed is 14 degrees, and the greatest heat has made the thermometer rise, in the shade, to 89. Within these limits are comprehended all the fermentable degrees, and consequently those necessary for carrying on the process of brewing. If the lowest degree proper for fermentation be 40, and the highest 80, the medium of these two would, at first sight, appear to be the fittest for this purpose; but the internal motion, necessary to carry on fermentation, excites a heat superior to the original state of the must by 10 degrees. Hence, if 60 degrees be the highest eligible heat a fermenting must should arise to, 50 should be the highest for a wort to be let down at, to begin this act; which heat can only be obtained, when that of the air is equal thereto, so that it denotes the highest natural heat for beers and ales to be properly fermented. With regard to the other extreme, or the lowest heat, however cold the air may be, as the worts, which form both beers and ales, gain, by boiling, a degree greatly superior to any allowed of in fermentation, it is constantly in the artist’s power to adapt his worts to a proper state. The brewing season, then, may justly be esteemed all that part of the year in which the medium heat of the day is at or below 50 degrees: this, in our climate, is from the beginning of October to the middle of May, or 32 weeks; the most elegible period of time for brewing all kinds of beers.
But, as many incidents often make it necessary to extend these limits, the only time for venturing to comply therewith is, when the medium heat of the season is at 55 degrees; by which, six weeks more may be obtained. But, under these circumstances, the quantity of beer brewed should be less, that the worts may cool more readily, by being thinner spread; and, to gain more time, the brewing is best carried on with two worts only: taking these precautions, and beginning early in the morning, the first wort, by laying long enough in the coolers, will, towards evening, be brought to a heat of 55 degrees. The night, in this season of the year, being generally colder by 10 or 12 degrees than the medium heat of the whole 24 hours, the second worts may be reduced to a cold of 43 degrees: the mean of 55 and 43, being 49 degrees, would be the real heat of the worts in the ton; and with 10 degrees more, (the heat gained by fermentation,) still it would not reach 60 degrees, the highest fermentable heat, beers intended to preserve themselves long should arrive to; but so near would it be to this, and so little is the uniformity of the heat of the air to be relied on, that necessity alone can justify the practice of brewing such drinks, when the heat of the air is so high as 55, consequently, where it exceeds this, it should never be attempted.
As the extractions are made by heats far superior to any natural ones, though the actual temperature of the air neither adds to, nor diminishes from, their strength, yet it is to be known for the following reason. The proper heat given to the mash is by means of cold added to boiling water; and cold water generally is of no other heat than that of the air itself. Indeed, when the cold is so intense, as to occasion a frost, and to change water into ice, that which is then used for brewing, being mostly drawn from deep wells, or places where frost never, or but seldom, takes place, may be estimated at 35 degrees, and this will be sufficiently exact.
The following table shews the temperature of the air for every season in the year, and confirms what I have just now said concerning the season proper for brewing, and the actual heat of the water. It was deduced from many years’ observations, made with very accurate instruments, at eight o’clock in the morning, the time in which the heat is supposed to be the medium of that of the whole day.
A TABLE, shewing the medium heat, for every Season of the year, in and about London, deduced from observations made from 1753 to 1765, at eight o’clock each morning.
| Degrees. | Degrees. | |||||||
| January to | 1 15 | } | 36´ 38 | July to | 1 15 | } | 60´ 52 | |
| to | 31 | } | 34´ 97 | to | 31 | } | 34´ 97 | |
| February to | 1 14 | } | 35´ 51 | August to | 1 15 | } | 59´ 89 | |
| to | 28 | } | 38´ 11 | to | 31 | } | 38´ 48 | |
| March to | 1 14 | } | 37´ 99 | September to | 1 15 | } | 55´ 17 | |
| to | 28 | } | 39´ 72 | to | 31 | } | 54´ 13 | |
| April to | 1 14 | } | 43´ 13 | October to | 1 15 | } | 48´ 66 | |
| to | 28 | } | 46´ 04 | to | 31 | } | 46´ 72 | |
| May to | 1 14 | } | 49´ 05 | November to | 1 15 | } | 42´ 26 | |
| to | 28 | } | 55´ 67 | to | 31 | } | 39´ 40 | |
| June to | 1 14 | } | 57´ 20 | December to | 1 15 | } | 38´ 61 | |
| to | 28 | } | 59´ 14 | to | 31 | } | 37´ 54 | |
To ascertain the authority of this table, and to make it useful to several purposes, I have carried to decimals the mean numbers resulting from my observations.—But such an exactness has been found, in the practice of brewing, to be more troublesome than necessary. I have therefore constructed another table, similar to the former, but where the fractions are omitted, and the whole numbers carried on from five to five. The heats of the latter end of October, and beginning of November, have here been set down rather higher than they really are; as, at this time of the year, the hops fit to brew with are old and weak, and I could not devise any means more easy to allow for their want of strength.
A TABLE, shewing the medium heat of the air, in and about London, for every season of the year, applicable to practice.
| Degrees. | Degrees. | |||||||
| January to | 1 15 | } | 35 | July to | 1 15 | } | 60 | |
| to | 31 | } | 35 | to | 31 | } | 60 | |
| February to | 1 14 | } | 35 | August to | 1 15 | } | 60 | |
| to | 28 | } | 40 | to | 31 | } | 60 | |
| March to | 1 15 | } | 40 | September to | 1 15 | } | 55 | |
| to | 31 | } | 40 | to | 30 | } | 55 | |
| April to | 1 15 | } | 45 | October to | 1 15 | } | 50 | |
| to | 30 | } | 45 | to | 31 | } | 50 | |
| May to | 1 14 | } | 50 | November to | 1 15 | } | 45 | |
| to | 31 | } | 60 | to | 31 | } | 40 | |
| June to | 1 14 | } | 60 | December to | 1 15 | } | 35 | |
| to | 28 | } | 60 | to | 31 | } | 35 | |
As nothing is so inconstant as the heat of the air, we are not to be surprised when it deviates from the progression specified in the table. The flowing water used in the brewery, at the coldest seasons, we have fixed at 35 degrees, and the highest heat in the air, to carry on the process for beers brewed for long keeping, at 55 degrees. The length proper to be drawn, or the quantity of beer to be made from each quarter of malt being fixed, the brewer, at any time, has it in his power to make calculations for brewings, supposing the mean heat of the air to be at 35, at 40, at 45, at 50 and even at any degree of heat whatever, so as never to be unprovided for any season. Water, being a body more dense than air, requires some time to receive the impressions either of heat or cold, for which reason the medium heat of the shade of the preceding day, will most conveniently govern this part of the process, unless some very extraordinary change should happen in the atmosphere. This must make the business of the artist, in this respect, very easy, as, in the course of his practice, he will have only to correct the little changes that occasional incidents give rise to; and the calculations will answer all his purposes so long as the lengths of beer to be brewed from the same quantity of malt remain unaltered, and with very little variation and trouble, when the coppers employed, by being changed, are of different dimensions.
The best method to know the true heat of cold water, would be to keep a very accurate and distinct thermometer, in the liquor back; but as this, in every place, is not to be expected, and inaccuracies must arise from a change in the air, to prevent their consequences in practice, we must have recourse to experience. This has taught us that a difference of 8 degrees, between the actual heat of the water, and that from which the brewing was computed, will produce, in the first extract, a difference of four degrees.
Most brewers’ coppers, though they vary in their dimensions, are generally made in proportions nearly uniform; the effect of one inch of cold water more or less, will therefore nearly answer alike, that is, it will alter the heat of the tap, by 4 degrees. But this will only hold good in such cases, where the water is in the same proportion to the volume of the grist. In brewing brown beers, or porter, three worts are generally made; the extracts therefore must be of different lengths from what they are in beers brewed at two worts only. In this case, the quantity of water for the first wort, is less than it otherwise would be; and what must be allowed for the first mash, to wet the malt, is so much as to occasion the second, or piece liquor, to be proportionably less also; as it is of great consequence, if the first tap doth not answer to its proper degree, that the second should be brought to such a heat, as to make up the medium of the first and second extracts, the second, or piece liquor, by reason of its shortness, is more conveniently, and more exactly tempered in the little copper; and one inch cooling in, is in this case found, both by calculation and experience, to occasion a difference of one degree of heat only in the mash.
One of the principal attentions, in forming beers and ales of any sort whatever, is that they may come to their most perfect state, at the time they are intended to be used. Common small beer is required to be in order, from one to four weeks, and as it is impossible to prejudge the accidental variations, as to heat and cold, that may happen in any one season of the year, it is rational to act up to what a long experience has shown, is to be expected, and to mix such quantity of cold water with that, which is made to come to ebullition, as to bring the extract to the degree fixed for each particular season, let the heat, at the time of brewing, vary therefrom, in any degree whatever.
In treating on the subject of air, in the former part of this work, I observed the effect it had in penetrating the parts of the malt, or in the technical term used by brewers, in slacking it. As such is the case, when the grain is entire and whole, it is more so when ground, and experience teaches us, that, when malt has been about 24 hours from the mill, the dampness it has imbibed is equal to half an inch more of cold water added to that which is to be made to boil for the first liquor, and produces therefore a diminution of 4 degrees in the heat of the tap11.
An effect, somewhat resembling this, is caused by the impression of the air on the utensils of a brewhouse, which are not daily used; the heat received from a foregoing process has expanded their pores, and rendered them more susceptible of cold and moisture. From this circumstance, the heat of the first mash will be affected in a proportion equal to half an inch less cooling in, or in the space of 24 hours, to 4 degrees of heat.
The time of the day, in which the first extract is made, becomes another consideration; for as 8 o’clock in the morning is the time of the medium heat in the whole 24 hours, the other hours will give different degrees. When a first mash is made about 4 o’clock in the morning, the following table shews the difference between the heat at 4 and 8; that of the other hours, in the like case, may be learned by observation. It has been observed, that, in the cold months, from the sun’s power being less, the heat of the day and night are more uniform, and also that the coldest part of the 24 hours is about half an hour, or an hour before sun-rising. I have judged it convenient to place, in the same table, the several incidents affecting the first extract.
Incidents occasioned by the air affecting the
heat of the first extract, to be noticed more
particularly, when small beer is brewed, as
the quantity of water is then greatest, and
the mash more susceptible of its impressions
.
| Morning at 4 o’clock* | ||
| January | 0 | Utensils, for want of being used, in 24 hours lose 4 degrees of heat, equal to half an inch of cold water. |
| February | 0 | |
| March. | 2 | |
| April | 4 | Malt, which has been ground 24 hours, imbibes moisture equivalent to half an inch, which lessens the heat by 4 degrees. |
| May | 6 | |
| June | 8 | |
| July | 10 | The difference between the actual heat of the air, and that naturally expected is to be allowed in proportion of 8 degrees to one inch cooling in. |
| August | 8 | |
| September | 6 | |
| October | 4 | Malts, from having been long kept, or old, become considerably slacked. |
| November | 2 | |
| December | 0 | |
* Colder by so many degrees than at eight o’clock in the morning.
Before we quit this subject, it may not be improper to observe, that, in the hottest season, and in the hottest part of the day, the difference between the heat of the air in the shade, and that in the sun’s beams in and about London, is nearly 16 degrees, and also that cellars or repositories for beers, are, in winter, generally hotter by ten degrees, than the external air; and in summer, colder, by five.