I've recently barrelled 40 pints of Turbo Cider (25 litres of Aldi apple juice, 1kg brown sugar and Safale 04). I let it ferment right down to 1000 before barrelling and put nearly a litre of apple juice in the barrel to prime. However, the result is a bit flat. It tastes ok, and I'm drinking it

If anyone could enlighten me that would be great, for future reference!
Cheers
Sam