Thanks for all responders - I have been forced to do some more research as I just could not believe the "one liter becomes two litres when one kilo sugar is dissolved" opinions. Cut to the chase - this is not correct, and in good scientific procedure, the proofs are given below.
Does adding sugar to water change its volume? Opinions differ...but not by much, here are three men of science – note that none of them say “the volume stays the same” or “1L water plus 1Kg sugar equals 2L liquid”! Although there are plenty on the internet that say just that.
“I have done several tests with various types of sugars (beet/cane/table sugar, dextrose sugar, dry malt extract) and they are all identical to each other within a few percent. The long and the short of it is that EVERY 1000 GRAMS OF SUGAR, WHEN DISSOLVED IN WATER, DISPLACES ABOUT 500mL OF WATER. (I.e. every gram of sugar displaces half its weight in water.)In other words, if you have 3 litres of water and you dissolve one kg of sugar into it, you end up with 3.5 litres of total volume of the solution.” Conclusion: 1 kg sugar will add 0.5L to a water volume.
“Yes, adding sugar to water DEFINITELY increases the volume. Dissolving sugar in water is a physical change, not a chemical reaction, it has nothing to do with the space between the molecules etc. 100g of sugar when dissolved in water, will contribute about 62.5 ml in volume ! This equates to 625ml per kilo – therefore, if you have 3 litres of water and you dissolve one kg of sugar into it, you end up with 3.625 litres of total volume of the solution.” Conclusion: 1 kg sugar will add 0.625L to a water volume.
“Adding sugar to water the volume will definitely change but not so much, for example….adding 1kg of sugar into 5L water will be equal to 5.7L [Not 6L].” In the above examples therefore if you have 3 litres of water and you dissolve one kg of sugar into it, you end up with 3.7 litres of total volume of the solution. Conclusion: 1 kg sugar will add 0.7L to a water volume.
So somewhere between 0.5L and 0.7L – let’s take the midpoint 0.625L multiplied by my own original query regarding 3.5K of sugar in 6L water, my 6L water becomes 8.18L total liquid. This enables me to adjust the amount of water needed to top up to 22.5L as in the recipe : 22.5 – 8.18 = 14.32L. As I am making a kit wine here from concentrated grape juice I will need to deduct from the 14.32 the volume of grape juice 1.49L = end result 12.83L.