Grapefruit Fermentation Super Speed

[AdamBrandy]

I have never seen fruit juice ferment so fast as this grapefruit must! On all my ferments I use Actiflore F-33 yeast by Laffort. Usually - no matter if I ferment my squeezed apple must, date syrup wash or bitter orange - they take two weeks to finish fermentation. This time I squeezed about 15 gal of grapefruit juice (red and white), added two kg of brown sugar, pitched in 10 gr of nutrients and 20 gr yeast - and after four days of vigorous ferment the airlock stopped bubbling. I checked the hydrometer and it seems to have dried out. No sweet on the tung neither. How is this possible? Anyone has an explanation?
*It can't be temperature because it was between 14-21 degrees celsius all the time.

[joeymac]

Man, that sounds tastey to begin with. What'cha makin'?

[AdamBrandy]

Fruit brandy. Lets see how it comes out...

[Pikey]

Sounds interesting, not much sugar - does grapefruit have a lot in it to start with ?

[joeymac]

Grapefruit juice only has about 22g sugar per cup... or 5.28kg in 15 gallons. Plus the 2kg of brown sugar
7.28kg of sugar only makes about 7.5% potential alcohol so it should ferment out pretty quick.

[AdamBrandy]

Makes sense - less sugar equals shorter fermentation.
Thanks!

[Pikey]

I think you've got enough flavour to increase the sugar some.

[edit - there's a lot of acid in grapefruit for those who think low PH is a Bad thing ]