Cidery Flavors when Kegging

Hello out there,

A few months back I made an extract nut brown ale. It fermented for about 4 weeks, and I was ready to keg. The sample tasted very good. So I transferred the beer to the keg in my apartment where the kitchen sometimes is above 90 degrees. I lived upstairs at the time and had window units. So I took the beer out of the fermenter and transferred it to the keg. The next time I sampled, bam, I tasted cider. Does anyone know what might have happened? My theory is that the beer got too hot in the kitchen while transferring...

I made sure that I was very thorough when washed and sanitized the keg. I let oxyclean sit in there for a few days, and ran it through the tap. Then I sanitized with starsan which I also ran through the tap.

Any ideas?

It's acetalaldehyde. Those cidery/green apple flavors are produced in a few ways: One is just incomplete fermentation, another is oxidation of alcohol into acetic acid (most likely in your case), and the third is contamination by an acetic acid bacteria.

If I had to guess, i'd say the beer was oxidized when you racked it into the keg. Next time when you clean out your kegs, just use the Star San and a scrubby brush. Be very careful to slowly rack your beer using a slow flow racking cane that's completely submerged. An auto siphon works well to transfer your finished beers, too.

Flush the keg with Co2 before filling with beer. I have threaded ball connectors for this reason, connect the beer fitting to you Co2 and this will let it fill from the bottom of the keg. Co2 being heavier than o2 will force it up and out. Hold a lighter at the top and when it goes out the o2 is flushed out of fill with beer and enjoy.