The thermometer used to control the malting and the brewing processes.
The principle of temperature measurement was established by the experimental philosophy as early as the 17th century. The measuring instruments are close to the modern thermometer: a liquid enclosed in a glass tube expands or contracts. Medicine, the first meteorological records, and also the laboratory physics make use of this kind of "thermometer". The notion of calorimetric degrees materialised by graduations is stated around 1700
The graduated scale of the Polish Daniel Gabriel Fahrenheit (Gdansk 1686~The Hague 1736) is becoming familiar in the Netherlands and Great Britain. Fahrenheit invented the mercury thermometer in 1715, graduated from 30 (intense cold of an aqueous solution of ammonium hydroxide mixed with snow) to 96 (temperature of a healthy human body) .
In tandem with this expensive thermometer for the scientist, instrument manufacturers design and sell thermometers suitable for every professional use. The subdivision systems are manifold, as are the calibration of boiling points or other changes in the physical state of the material taken as benchmark points.
The brewers have a great practice of temperature control (steeping, boiling of the wort, cooling, fermentation). For their part, maltsters, who organise themselves as a complementary but distinct profession from brewers, must also control heat, its effects (germination, drying, browning of the grains), and record their heat measures to repeat and improve their malting technical processes.
Contrary to what the learned circles then repeat, the men of practice also know how to abstract general rules, set scales and evaluate without a thermometer the changes of state of the materials they transform. They know that the infusion of malt requires different heating stages to obtain a sweeter wort. These stages vary according to the quality of the malts (pale, coloured, roasted).
The brewer is also a maltster who knows how to adapt the right temperature for drying the germinated grains. Scientists often hide the source of their practical observations. The notion of temperature stages was part of the apprenticeship of the good malt-brewer. The use of a thermometer was recommended in hop drying as early as 1733 and was quickly adopted, because a visual assessment of air temperatures (slow drying of hop blossoms) is very difficult and misleading, depending on the season.
Michael Combrune, a Huguenot brewer who lived in Hampstead and then in a village in the London metropolis between 1740 and 1750, is usually considered to be the promoter of the brewery thermometer for Great Britain. His Essay on Brewing of 1758 is the first known text recommending the use of thermometers to brewers. In 1762, Combrune published Theory and Practice of Brewing. From the theoretical principles are derived the detailed practical instructions he gives to improve the production of the various kinds of beer then common in England. He advocates the measurement, control and recording of temperatures at all stages of brewing. Combrune suggests that the first thermometer was into the hands of a brewer in 1740, less than 25 years after the first experimental Farhenheit's thermometer. John Richardson John Richardson published similar works at the same time (Advertisement of Proposals for teaching his Method of brewing Porter and Pale Beers, in 1777, and The Principles of Brewing, Hull 1798).
Nevertheless, Combrune adds that most of his contemporaries quickly discarded this instrument without finding any use for it. Not out of obtuseness, but because they have their own reliable means of detecting temperature changes in brewed liquids and grains. Every Man His Own Brewer, published anonymously in 1768, indicates that the thermometer was in general use among the London breweries of Porter. Brewers had specialised thermometers built for their profession: robust, suitable for tanks and pipes, graduated according to key brewing temperatures, and sometimes silent to protect their secrets.
Once adopted by brewers and widespread within the brewery, the thermometer itself will generate further technical innovations. Beer types that are more delicate to brew and control, such as traditional ale, will be produced on a large scale all year round in new industrial breweries in English provincial towns. The quality of their water supply will be the dominant theme of the 19th century (Burton-on-Trent), an efficient advertissement against the beers brewed with the polluted waters of the big cities.
In Bohemia-Moravia, the adoption of the brewery thermometer is acquired around 1788. The brewer František Ondrej Poupe (1753~1805) used it and advocated its widespread use and that of the hydrometer in all breweries in the country. He wrote three technical books on brewing.
What forces tipped the balance at the end of the 18th century? More than an immediate technical advantage, the thermometer was adopted for economic and fiscal reasons, at least in Great Britain.
At the end of the 18th, the production of beer for the big cities of the industrial revolution becomes annual, and no longer seasonal (spring beers, beers sold at best 6 months in the year). In today's vocabulary, we would say that the economic model of the brewery is changing. The successful brewers in England supply beer to an urban population that drinks all year round. This beer has to be brewed throughout the year, even in summer, on a short cycle (shortened on-call period). The old rural and domestic pattern is maintained (brewing in autumn and winter a beer served in spring and also in summer, but with a lot of manufacturing or conservation accidents) when the quantities produced and the risks are low. The rural brewer combines several seasonal activities, brews only small volumes and serves its immediate environment. A permanent brewing all year round changes the situation. Controlling brewing in summer becomes crucial. The thermometer is there to help the brewer compensate for seasonal temperature variations that he cannot anticipate or measure. For the urban brewer, each brew now involves thousands of hectolitres and a real financial risk. Brewers who adopt the thermometer fall into this category from the outset and did not need to be convinced a priori.
A second impulse will push the reluctant brewers on the way to physical measurements in the brewery. This is the Excise Administration. The European state powers committed themselves in the 19th century to an economic policy of heavy taxation to finance their colonial ambitions. The malthouse-brewery is an inexhaustible source for the treasury of each country. The excise duties of the beer brewing are calculated on the basis of the raw grains and malt bought and the volumes of beer sold, according to each sort of beer. The brewers will then optimise the conversion of starch into sweet wort and the fermentation of the latter into an alcoholic beverage. From a tax point of view, the malt that is not fully converted into fermentable sugars and the starch that remains in the spent grains (dregs) are a "dry" financial loss ".
 Gabriel Fahrenheit does not use the boiling point of water which depends on atmospheric pressure. However, in 1724 he indicates that this point is at 212 degrees on his own scale on his own graduated scale.
Un article de synthèse sur la question des mesures et de la brasserie aux 18è-19è siècles : Freudental Gunter 2003, Von Wettergläsern, Wärmemessern und Bier-Waagen und den Anfängen der Betriebskontrolle. Gesellschaft für die Geschichte und Bibliographie des Brauwesens, Jahrbuch 2003, 53:78.
 Water does not immediately impose itself as a physical referent, despite the advice and authority of Newton in London or Willem's Gravesande in Leiden. After Fahrenheit's death, Hendrik Prins and other manufacturers has reproduced his mercury thermometers, but calibrated with the melting point of ice (32°F) and the boiling point of water (212°F).
 Sumner James 2007, Michael Combrune, Peter shaw and commercial chemistry : the Boerhaavian Chemical Origins of Brewing Thermometry, Ambix 54-1. Re-editing of M. Combrune's book in 1804 under the title Theory and Practice of Brewing : openlibrary.org/books/OL7247997M/The_theory_and_practice_of_brewing.
 The graduations are removable, but fixed to the shape of the tube and calibrated according to its use (mash tun, wort cooking, fermentation). Reserved for the master brewer, it is his privilege to read the thermometer.
 Paupie, F.A. Die Kunst des Bierbrauens physisch-chemisch-oekonomisch beschrieben (The art of brewing described in physical-chemical-economic terms)(Prague 1794); Versuch einer Grundlehre der Bierbrauerei etc. (Essay on a theory of brewing, etc.) (Prague 1797). Pocátkové základního naucení o varení piva etc. (Fundamentals of beer brewing, introduction etc. (Olomouc, 1801).