Acetaldehyde In Aroma

[Adr_0]

awesome thread. on a side note, good to see people comparing apples to apples

 

[Acasta]

Just split another batch brewed today. Half into plastic, half into glass.

Very interested to hear some more results on this.

 

[manticle]

Acetaldehyde is perceived by most people as that taste you get when you sink your teeth into a granny smith apple.

With that in mind, you'll know it when you taste it.

Martin

Also pumpkin skin and paint emulsion. None are great in beer.

 

[O-beer-wan-kenobi]

Exactly the same here, thought it was an infection in the lines/taps. Everything cleaned and disinfected, replaced the taps, still the same.

Just split another batch brewed today. Half into plastic, half into glass.

Screwy

Screwy, How did the brews turn out?
Again I have acetaldehyde in my Vienna lager. Im going over my process and cant see where it is coming from.

I dont use an oxygen stone but I run the wort into the fermenter from a height that helps with oxygenating the wort then I give it a good shake for a minute. The yeast pitching rates are high so I'm baffled where this comes from? I'm wondering if it is the plastic fermenter releasing oxygen back in to the fermented beer.

When I have taken gravity readings at 2 and 3 wee weeks the beer tastes good but after 4 weeks or so I can detect the green apple smell and flavour. Either the smell and flavour are strong or I am sensitive to this because it is not feint.
All the advise for acetaldehyde is to keep the beer on the yeast for them to clean up and remove it but it seems the longer I leave it the worse it is.

So this makes me think, is it the fermenter slowly leaking oxygen back into the beer? My fermenter's are a few years old and it would be good to see if it is the cause or not.

 

[technobabble66]

Don't know if this is drifting OT or not, and whether there's a better thread for it, but it seemed relevant:

http://www.mocon.com/pdf/optech/Closures%20-%20Oxygen%20Passage%20Study.pdf

It's a study looking at the O2 permeability of different bungs & airlocks (primarily for glass carboys). I thought it particularly interesting as it gives a nice summary of the oxygen permeability of various plastics, etc.

In particular:
HDPE (fermenters) = 44-91
LDPE (glad wrap) = 98-138
PET = <1-1

Also, with the bungs/airlocks, it seems Silicon is very permeable to O2 (well, i didn't know that) and the problem with water trap airlocks is not only the permeability of the plastic, but that the water can allow easy transfer of O2. Still water apparently allows significantly less O2 transfer, but still some.

So if we're concerned with O2 getting into our fermenting/conditioning beer, maybe we should be moving to glass carboys with dry/mechanical air-locked non-silicon bungs.

I should probably say i don't think i've yet experienced any problems with my brew i'd attribute to O2 getting into them, but the findings above are interesting nonetheless.

 

[O-beer-wan-kenobi]

Thanks Techno. Not sure how those numbers for the fermenter materials exactly relate to the amount of oxygen you can get in the beer, and how much oxygen you would need and the duration to get the acetaldehyde flavours and smell. (sorry lots of and's there)

Like I said my fermenter's are old which may be a factor, but I would have thought this would be an issue that has come up before, considering the fermenter's are common standard ones.

I have a 25l glass demijohn but I have already started another lager, so I may try and secondary ferment in that which is something I have never done before. I will see if that makes a difference, if not I will primary ferment in glass the next time round.