Increase ABV of existing homebrew?

Just a theoretical chemistry question.

Is it possible to take an existing homebrew, or any beer for that matter, add sugar, then pitch yeast to increase alcohol content?

Not that I'm planning on doing it ... just curious if possible.

Basically you would be re-fermenting an alcoholic beverage that has already fermented.

Any thoughts?

That's all there is to it. But you run the risk of throwing the beer out of balance and turning a good thing into high-alcohol plonk. Occasionally, I've added some sugar to dry out a beer that had too many fermented sugars at the end.

Considering you'd probably be adding oxygen in the process and oxygen+beer=oxidation I'd say it's not something you'd want to do.

This is essentially what alot of people do when brewing big beers like triples. They let the yeast ferment out most of the maltose then add the simple sugar when they are approaching their final gravity.

On the CYBI show where they cloned DFH 120 min IPA, the brewer let it ferment almost all the way out then fed it sugar everyday for I think 2 weeks. I'm not sure if this is the way DFH does it.

The difference between this and using a totally finished beer and adding sugar and yeast is that they are using the existing active yeast and just prolonging the fermentation to raise ABV.

People do this rather than add all the sugar at the end of the boil because yeast have a tendency to eat the most readily available food, which is simple sugar. Then they have a hard time with the more complex maltose that is still around.

Think of it as giving your kid with a plate of vegetables and cake. They will fill up on cake and not eat the veggies. You need force them to eat the veggies first then give them the cake. Kids will always have room for desert and yeast usually have the capacity to eat simple sugars even in a high ABV wort.

Sounds like a great idea. I may try this on my next batch since im already 3 days into my secondary. What is a good simple sugar to use and about how much each day?

This is exactly what happens when people bottle. Add corn sugar to already fermented beer.