@cire Thanks for the info. Any chance that you have a source for this pH? The historic papers all just say "it is neutralised".
Ragus. Somewhere in their website was a description of the processes they used. Whether it is still there is in doubt as it appears they no longer produce in bulk the 25kg blocks of Brewer's Invert 1, 2 and 3. The latest I saw advised they made Brewer's Invert to order for British and Belgian brewers, "Custom Formulations". I am finding most of the links that provided details of their processes are no longer accessible, but this one does give the information on neutralization you asked.
https://www.ragus.co.uk/product/invert-sugar-syrup/
I'd be careful what you read about early inverts, there was at least one case where a brewery in Manchester used invert sugar manufactured in Gargrave near Liverpool, that killed a number of heavy drinkers.
Invert sugar manufacturing was what brought Mr Tate and Mr Lyle together in business.
There are several ways of making invert sugar, invertase is an enzyme that will convert sucrose to glucose and fructose at room temperature, but takes many hours.
Inversion takes place with heat alone, but is time-taking. It can be done more quickly or with less heat by acidification. Ragus acidify to pH 1.6 and keep at 70C, and while stirring continually, take samples until full conversion, when it is neutralized to stop the process and avoid further chemical changes.
I invert at pH 2.2 at a light simmer for 5 to 15 minutes. Like Ragus, use 2:1 ratio sucrose:water by weight. At this ratio, the sugar goes fully into suspension, but not fully dissolved so the mixture is quite hazy. Stirring makes the solution clarify seconds after adding the requisite amount of acid, showing conversion is underway. As the mixture reaches a simmer, another 5 to a maximum of 10% of sugars can be added, some of which will also invert. A 10% addition will likely result in some crystallization of the final product, while lesser amounts will remain liquid and clear when cooled. This is quite imperfect when compared to the way Ragus work, but it does do the job. It is so simple a process that I would advise a first attempt is done using all white refined sugar, even if only on a small scale. Observe the sugar going into solution and clearing when the acid is added. Then look for a slight change in colour to pale straw/yellow when inversion completes. Knowing this process enables timing of inverting or adding darker sugars.
With soft or RO water, 1kg or 2 pounds of sugar will require a good level teaspoonful of citric acid. For alkaline water, add a well heaped teaspoonful. I add acid when the mixture reaches 70C. 2gm of sodium bicarbonate should be enough to neutralize to pH 5 or thereabout.
Few British breweries now include sugars in their recipes, it is too expensive compared to the cost of malted grains. Those can't make the same beers as sugars can.