increase alcohol content and dry the beer by adding sugar, best way

I am fermenting my RIS (83% m.otter, 6% crystal 11%roasted) mash 65 ° C, us05, OG1.100 and after 2 weeks FG1.031, I added sugar (20g / L) to increase 1abv to the secondary and fermentation is immediately re started. Is this the right way?

 

Yes, adding sugar will do exactly that. Yeast loves sugar so just let it ferment.
Be careful tho Adding to much sugar will have a detrimental effect on the body of the beer. So if you feel like you need to add to much sugar it might be better to use DME.

 

You put your sugar addition in a little later than I do for your late addition, but that's not necessarily bad. I try to add my sugar right at or shortly after peak fermentation. I try to make sure that the yeast are all fired up for a big sugar meal. The fact that your fermentation kicked right off after the addition means your yeast were still active.

No worries. Should be a nice RIS if your final gravity end up in the high 20s.

 

after 5 days it drop to 1.026. now is 10%. I think it makes no sense to add more sugar

 

Going to be a bit thin for an RIS, but I just had left hand's wake up dead, and despite being thin it is quite delicious. Good luck with your beer.

 

When doing big beers you definitely want to add the sugar towards the tail end of fermentation so that the yeast can take care of the more complex sugars first. Unless you're doing a DL clone, then just add some kikkomans.

 

I added one lb of Simplicity sugar to my saison after the boil but before placement in the primary. Kind of curious to see what happens.