Higher Alcohol content question

I have seen some porters labelled as 15+ percent ABV. The yeast that I have been using, scottish ale yeast reports about 8-9 percent ABV. How are these porters getting the higher alcohol content?

Are they pitching Champagne yeast in addition to the ale yeast? Are they adding distilled liquor to the fermentation?

Any advice would be helpful, thanks in advance.

There are beer yeasts that claim to be able to get to 25% abv.

a 8/9% yeast has been able to muster 12% with step fermentation and even bottle carb with some care.

They legally cannot add spirits and still call it beer.

Most ale yeasts will actually go up to 12% if not a touch higher if treated right. It's all about acclimating the yeast to the hostile environment. Almost all strains of yeast were conditioned a certain way to make them do what the brewer wanted. A good example is Wyeast 1728 Scottish and 3522 Ardennes. Believe it not, it's the same strain of yeast. But obviously 3522 was conditioned over many generations to do a very different job.

But yes, many breweries add champagne yeast towards the end of fermentation to make sure the beer gets to where they want it to be.

Step fermentation is what DFH does with 120 and Utopias. Small base malt and dextrose additions in combination with more nutrients and pure O2 additions. The principle is to keep the active fermentation going... and going.... and going.....

I know the 120 regimen takes well over a month of daily supplemental sugar and O2 feedings.

Another possibility is to do a rum wash, which is to brew both the base beer and distill some rum (yeah, illegal as hell without the proper licensing) and then blend the two together. Seems lazy to me.