Botteling, blending, sweetening, syrup

my first cider is made, and I’m happy that I had no problems with it.
picking day was on the 3rd of October last year, and I have around 300litres (arround 80 gallons)
I have a couple of problems now, which I will solve like this, please give me any advice you can give me:

first is, that I have no more sugar in my Cider, it’s totally dry, but I want it sweet, so i will put 20grams of sugar per litre in there. I just have around 5 litres of apple juice left, so I can’t backsweeten it! I will do it different this year.
I haven’t pasteurised the cider yet, and I don’t think that I can do that due to the amount of Cider I have, how can I kill the yeast completely without pasteurising it? I need to kill the yeast, because I will put sugar in it again, and I want to store it for more than one day. any idea? how do you store your cider?

next is, that I want to give it a taste of elderflower, in may/june i can collect elderflowers for making a syrup, do you have any receipe? and how much elderflower syrup do i have to blend with cider? i guess it depends how strong the elderflower syrup is, isn’t it?

I will buy a 50-litre keg, some fittings and a bottle of CO2 for carbonating. next step will be that i will put CO2 in the cider-keg, I read this way of carbonating anywhere in the network, do you think it will work?
currently my cider is just a bit sparkling, but I want it really sparkling.

I bottle the cider and will close them with crown caps, do i have to sterilse them before i close them? And how can I make it, that there’s no more air in the bottle when I close it? I see no way for putting CO2 in the space between cap and cider. any idea?

thx for any advice you can give me!

Congrats on your first batch of cider! The easiest method to back sweeten the cider will be to dose with potassium sorbate as the recommend dosage of 1/2 tsp per gallon. Stir in the sorbate and wait at least 24 hours before introducing sugar. The only downside is that one treated you will need to either bottle the cider still, or force carbonate with a keg and c02 in order to achieve carbonation.

To sweeten cider you can do any one or a combination of things. You could add the the left over juice that you have, or freeze the juice and then invert the frozen open bottle over a glass to collect the run off as it thaws. The run off will have a sweeter more concentrated apple flavor without adding the additional volume of liquid to your batch. You could also utilize wine conditioner which is liquid inverted sugar, or make your own simple syrup by dissolving corn sugar or table sugar in a small amount of boiling water.

Don’t forget to take gravity readings pre and post sweetening so that you gain understanding of the FG that your palate prefers. Above all else, add the sweetener of choice slowly, tasting a lot the way. Adding sweetener to cider is a lot like adding oak to wine. You can easily add, it’s pretty hard to remove if you end up with too much.

I would recommend continuing to bulk age a portion of the batch in a sealed carboy until elder flower or other fruits come in to season. Be sure at this point to fill the carboy all the way up the ned and use a solid bung if available to prevent oxidation. Once flower and fruit become available you can rack off on to the preferred additive and then rack to keg once the flavor is achieved.

Good luck!