The different styles of sweetness in sparkling wine can sometimes get a bit confusing. The reason for this is that historically the wines were much sweeter than there are now. And as time has gone the preference has turned more and more to the drier, and new styles has been introduced to the market, and hence new names.
Here is the short list:
Brut Nature: max 3 gr sugar/litre (no added sugar allowed)
Extra Brut: max 6 gr sugar/litre
Brut: max 12 gr sugar/litre
Extra seco: 12-17 gr sugar/litre
Seco: 17-32 gr sugar/litre
Semi-Seco: 32-50 gr sugar/litre
Dulce: more than 50 gr sugar/litre
Seco means dry, and was the original “starting point” in the sweetness scale, with Semi-Seco as “half dry” and Dulce meaning sweet or dessert.
When people wanted dryer bubbles Extra Seco (extra dry) was created and when that was not enough Brut was created, later followed by Extra Brut and finally Brut Nature.
Brut Nature never has any added sugar, only remaining fruit sugars from the juice, that has not been consumed in the fermentation process. So here the scale stops and we will never be able to produce anything dryer.
Dulce being the very sweetest Cava is very hard to find nowadays, since the trend is all about dryness. I think this is a shame since Cava Dulce is very nice to desserts like chocolate cake or crema catalana. Luckily some producers still make them.