That should do a perfect job, but Ragus, the UK firm that makes Invert for brewers, start with refined cane sugar as described half way down this page.View attachment 736995
This one. I actually don't know how this translates correctly into English but my best guess is raw cane sugar. It is only centrifuged, not fully refined so it is slightly brown-ish. The picture gives a good idea.
To my knowledge, that's what's actually being used by the companies that produce brewer's invert the traditional way.
Now 70C is the precise temperature Ragus invert their sugar, but that is done at < pH 1.6. I tried that pH while simmering and the result was a total disaster with over half the sugar destroyed.I actually didn't heat it strongly before it went into the oven, I only dissolved everything and now the oven does the rest. Takes forever though... It was around 70c when it went into the oven.
I use double the weight of sugar to water, heating it to 70C when it will nearly all dissolve. The an amount of acid is added to the mixture with heat is still applied,. The amount of acid is that which would reduce the pH of the water used (without sugar) to between pH 2.2 and 2.0. It is then simmered as described here, watching the color change from white to pale a yellow/brown tinge. For darker invert, rather than cooking it further, such as molasses/blackstrap or Black Treacle is stirred into the mix to obtain the desired color/flavor. To stop the process, a small amount sodium carbonate or precipitated chalk is carefully stirred in and the resultant product allowed to cool.
I have no doubt all the processes previously described produce excellent products for making beer, but just wanted to describe the process I use, using Tate and Lyle refined cane sugar which costs me the equivalent of about 20 cents a pound.