Could Adding Beer Sugar Help Increase Alcohol Level

No. This is often stated but it is not the way it works. When simple sugar is added to your wort/beer it is completely fermented (assuming the yeast remain healthy) and it is easy to compute the alcohol produced. This is identical to bottle carbonation except on a larger scale. Your FG is unchanged.

Simple sugar can be used to dry out a beer, but this is done when the recipe is created. Example: I want a double IPA in the 8 - 9% alcohol range. If I added enough grain to accomplish this it is likely the beer would result in a higher than desired FG. So grain is eliminated and replaced by sugar. The result is a high OG with a low or medium FG (remember, all the simple sugars are fermented). The monks in Belgium do this every day with their strong ales. They desire high alcohol and medium body and achieve this by substituting sugar for grain. My experience is adding sugar up to 5-10% of total fermentables . . . the monks go higher than this.

Adding sugar in low OG brews is not normally done (better ways to dry it out) but you are trying to fix a problem. Using koopa's number you are talking about adding 2°P or 0.008 points. This will give you about 1% extra alcohol without changing flavor or color. Your beer will still have a thin body.

If you add malt extract there are more uncertainties as you are not sure of attenuation. Will the remaining yeast consume 70% or 80% or ???. The yeast have already adapted to the current fermentation, now you are adding a different source of complex sugars. I am not saying it will stall, but the risk is in not knowing. Expect color and flavor to change also.

This is a long article, but here are more details on sugar.

 

Agreed! Sorry I wasn't clear about that in my last post.

 

You could try freezing the a beer and removing some of the beer Ice. I think I have heard of someone doing that in the past. You could save the batch, just have less, and not have to wait for the "second" fermentation after your sugar addition. It would also retain the good body.

 

You should ferment until attenuation is complete and there are no off-flavors. Yeast don't know about your calendar, regardless of whether you add sugar or not.

 

For a recipe designed to have sugar it is normally added during the boil which eliminates any sanitation problem. When I have added directly to fermentor I pitch right after high krausen. You probably want to run the numbers in brew software to check your outcome. I can see no advantage in waiting . . . your yeast are active and should require no additional time in consuming all the sugars. It is like serving a child a plate of vegetables and a bowl of ice cream . . . one goes at a slow rate and one goes fast.

As Vikeman says, your hydrometer will tell you when it is finished.

Unrelated to sugar: A technique to cover up a thin-body beer is to dry-hop with some nice aroma hops . This may be out of style for a Kolsch, but it could help with the problem. A drinker's first impression is "pleasant aroma" instead of thin body. When I dry-hop to mask a mistake I will split the batch and do some experimenting with hops. Good luck and it would be nice if you posted results with it is all complete.