Enough sugar??

[Memsy]

I'm brand new to this and need some advice please!

I have x3 4.5 ltr demijohns about 4/5 full (about 3/4 of which I am guessing is liquid and the rest is the squashed grapes & pips etc). In addition there is 1 pack of yeast (Gervin GV2) and 1 500ml Ritchies Red grape juice concentrate and then about 12 tsps caster sugar in each bottle as well (added over 3 separate occasions). They have been fermenting since last Wednesday - over the weekend they were bubbling like crazy and then over the last 24 hrs they have slowed to virtually no bubbles. So, twice (this morning and just now) now I have added a few teaspoons more sugar when I have re-mixed (by up-ending) the bottles. I suspect (from the very yeasty and dry taste) that it needs more sugar to keep the fermentation going. Do you think this quantity of grapes needs more sugar? If so, how much more?

Thanks!

 

[NorCal]

The yeast will live until they run out of food or the environment is not hospitable (temperature, alcohol %, nutrient etc). So if they are missing food and the environment is acceptable, more sugar will kick up the fermentation. Without a starting specific gravity measurement and one now, it's difficult to say if the alcohol is reaching the limits of your yeast.

If the environment is what is stopping fermentation, then the sugar you add will remain (residual sugar) and will serve to sweeten the wine.

 

[RonObvious]

It's really hard to say without knowing the specific gravity - both current and original. Do you have a hydrometer? If not, you'll want to get one. Making wine without knowing the specific gravity is like flying a plane at night with no instruments.