Desired Underattenuation

I recently made a Porter and wanted it on the sweeter side. I mashed around 156 and used a lower attenuation yeast (app 71 - 75% wyeast London Ale III)

I checked the gravity as I kegged it yesterday and was surprised to see it had only hit about 65% attenuation (I have yet to have a stuck fermentation) The OG was 1.063 and dropped to 1.022.

So I tried the beer after hooking up CO2 and WOW! It was really good, super sweet and malty like I wanted it. I usually like a more effervescent beer but I enjoyed a couple glasses of my new porter at room temperature and uncarbonated because it was just so thick and sweet.

Okay so my question: Is there some way I can ensure a lower attenuation again when brewing this in the future? I know the hotter mash helps, but I have yet to have one with this high of an FG. The other thing I think is I may not have hit it for very long with the oxygen tank. That should help too but does anyone know of a way to measure or accurately predict how much I have oxygenated the wort (I just go by time but actual oxygenation varies if the can is running low.)

Any help appreciated! Thanks!

I don't know of a simple, accurate way of measuring how much you've oxygenated the wort, but you should be able to control the attenuation via the use of camden tablets. Just start taking hydrometer samples once fermentation slows down, and when you hit your desired FG, add the camden tabs to kill the yeast.

It seems to me, that you might not need this (IMO). With the hotter mash and the less attenuative yeast, you're likely to have another similar FG again. you could always cold crash the primary once you near the desired FG. Then Keg it an keep it cold. It should take quite a while to dry out if you keep it cold.

You did two things intentionally to produce the result and were successful. You know the answer to your question already. Mash high.

Perfect, I hadn't heard of campden tablets before, but it sounds like that is just the key in case I can't get it right with just a high mash temperature. I seem to have attenuation fairies in my basement. I made barleywine a few months ago that went from 1.100 to 1.016. (aim was 1.025ish) I wasn't exactly thrilled about that since there isn't enough sweetness to balance out the alcohol warmth. It's good to have a way now to inhibit fermentation if the yeast are extra aggressive, thanks for the tip!