Yep, a teaspoon of conditioning sugar per 500ml bottle is about right. This is approximately 10g/L and will ferment into 4.7 g/L of C02. Since the density of C02 is just a bit less than 2g/L you will end up with around 2.3 volumes of C02 fizz per bottle.
However, be aware that adding granulated sugar to bottles is hard work and messy (that is why some people use carbonation drops). It is just as easy to make up a concentrated sugar solution (2 sugar to 1 boiling water, then let it cool) and mix it into to the bulk cider. This approach sanitises the sugar and avoids adding any spoilage nasties that granulated sugar might bring.
Rather than trying to calculate how much sugar solution to add, you can simply add it until the SG of the cider has increased by 0.005 (i.e. 10g/L) in your case, or whatever fermented SG results in the level of carbonation you are after. This applies regardless of the size of bottle you use. Using the sugar solution mixed into the cider also ensures an even distribution of conditioning sugar in the bottles.
A word of warning re sugar and SG calculations. You might find some sources give slightly higher “sugar” values vs SG than I have used. This is because in some sources, “sugar” is sometimes used loosely for everything that affects the SG of juice.
Although sugar has the biggest effect, there are other non-fermentable components like acids, tannins, flavours, etc that also affect SG. These non-fermentables can account for 15% of the SG. e.g. SG 1.050 juice is sometimes quoted as 130g/L “sugar” whereas it is 110g/L sucrose (proper fermentable sugar) and 20g/L non-fermentables.Two easy to get “proper” references for actual sugar vs apple juice SG are Claude Jolicoeur’s Table 8.8 and Proulx & Nichols P47 Specific Gravity Table.
Also, don’t get too hung up on SG1.000 being the “holy grail” that indicates complete fermentation. This is because the finished cider will contain the non-fermentable components that lift the final SG as well as alcohol which has a SG lower than 1.000 so pulls it down. It is just convenient that the combined effect of this is usually around SG 1.000 but depending on the mix, can typically be anything from 0.096 to 1.004. Hydrometer readings that are stable over time are the best indicator
“Thus endeth the lesson”… enjoy the journey.
Cheers!
