Cider Making – Strange gravity

I am making some cider at the moment. I have approximately 10 gallons (50 litres) brewing away. The juice was part of a bulk order from the nearby Millets farm which was split amongst members of our Oxford Brewing Group.

There is no recipe to speak of… basically I made some dried wine yeast (10 teaspoons) into a starter with a little brown sugar boiled in water and cooled. Pitched it into the apple juice in the containers I collected the juice in (food grade 5 gallon plastic). The next day it was fermenting out of the top and all over the floor… so I took it outside for a few days until it had calmed down.

Today (about three weeks after it started), I transferred one of the containers into a Hambleton Bard plastic pressure barrel. While I was at it, I measured the brix reading. According to my calculations this gave it a final gravity of 0.996, which is less than 1. I thought that was impossible. Water has a reading of 1.0000. So I also measured it with my hydrometer and came up with the same answer. I then tested my hydrometer in water and that measured 1 as expected.

If this is correct then this would mean all the sugar has been fermented out, and it would have an alcohol by volume of 9%. Tasting it, it still has a lot of sweetness, and it has not finished fermenting (gas was still being produced in the fermenter).

How can it possibly have a gravity of less than one, and still taste sweet and be fermenting?

It tastes quite nice.. a bit of sweetness, but also that real cider bite to it. It doesn’t have a lot of that sulphor smell and taste that cider often has when it is young. Last year it took several months to become drinkable.

Maybe someone else wants to check my calculations:

Original Brix was 16.2%, which equates to about 1067 gravity. Other members of the brew group got similar readings.

Brix today is 5.7%, and a hydrometer reading is 0.996.

This gives me an abw of 7.3% and abv of 9.1%.

There must be some other explanation for both the refractometer and hydrometer readings to come back with such a silly value.

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