Cidery Smell in Ale / Acetaldehyde

I've had an English style ale in primary for 7 days. The full details are in this thread:

https://www.homebrewtalk.com/f12/ipa-recipe-too-much-crystal-389047/

I popped it open to take a SG sample and noticed a strong cidery smell, which I have smelled before in other brews. My understanding is that this smell is due to acetaldehyde, and with time the yeast will convert this to ethanol.

My questions are:

1) Is this "bad" in any way, or just a normal part of the attenuation process i.e. RDWHAHB.
2) If it is "bad", how can I modify my process to remediate it?

The yeast still is chewing on it so I know this is still a work in progress, but otherwise SG is getting close to FG and the taste is fine.

Acetaldehyde is one of the intermediate products of fermentation. It's a normal thing. There may be ways to minimize it but it will always be there.

From what I can gather:

In an anaerobic environment, yeast transforms sugar -> pyruvate -> acetaldehyde -> ethanol (good!)

In an aerobic environment ethanol can get oxidized back into acetaldehyde (bad!)

So - is it possible to over-aerate your chilled wort, or does the yeast consume all of the available oxygen during the lag period of reproduction and before fermentation?

You can over aerate your wort but it takes pure oxygen through a diffusion stone and then it still takes some time. You cannot get too much by shaking or stirring. Some would argue that you can't even get enough oxygen by shaking or stirring to be optimal for the yeast health.

Excessive acetaldehyde (more than will be cleaned up by the yeast) can be a symptom of too high ferm temps, where was yours at?

So the general recommendation to avoid splashing and aerating your beer as you rack or bottle is just to avoid oxidizing ethanol to acetaldehyde.

And even so, so long as you still have a good yeast population it should scavenge any oxygen and re-convert that acetaldehyde back to ethanol so long as you condition in the bottle for long enough.

naiek said:

Excessive acetaldehyde (more than will be cleaned up by the yeast) can be a symptom of too high ferm temps, where was yours at?

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Primary is in my kitchen which usually stays between 65-68F. I pitched about 5g of dry Windsor ale yeast so it wasn't overpitched, so I doubt it got too warm.

It has a few more SG points to drop and it is still putting off gas bubbles, so I'm pretty sure it is still wrapping up the tail-end of the fermentation.

I have my fermenting beers in a 62 degree room and the outside of the fermenter will get up to 64 from the yeast activity. As the temperature goes up the yeast get more active and raise the temperature even more. It could be 4 to 6 degrees warmer than the room temp in your fermenter. Do you have a stick on fermometer to be able to monitor the temp of the beer? I've never been able to read them with any confidence so I use a non-contact IR thermometer. I can just point and shoot.

I keep a small spirit thermometer on the fermentor itself and it indicates these temperatures. This is a 2.5 gallon batch so it isn't a huge thermal mass.

I think you would be hard pressed to over oxygenate the wort prior to fermentation. The majority of my beers have receives oxygen via an oxygen stone and have not had any issues with cidery flavors.

I'd think most of these off flavors are either from unfinished fermentation or oxygenation post fermentation. And of those two I'd go with unfinished fermentation as the most common cause.

Keeping in mind some yeasts produce an ester profile similar to apples. A lot of British beers come across with apple aroma to me.

Edit - 7 days? Not finished fermenting.

chri5 said:

Keeping in mind some yeasts produce an ester profile similar to apples. A lot of British beers come across with apple aroma to me.

Edit - 7 days? Not finished fermenting.

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I'm definitely in agreement that it is not finished. Just curious about the process.

The esters are interesting too. Windsor ale yeast is said to be 'fruity'. What I am smelling is straight apple cider, smashed apples, which I don't know whether it can be fully attributed to yeast esters or not.

Thunder_Chicken said:

The esters are interesting too. Windsor ale yeast is said to be 'fruity'. What I am smelling is straight apple cider, smashed apples, which I don't know whether it can be fully attributed to yeast esters or not.

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I find a beer like Fuller's ESB smells very apple-like to me.

I'm hearing that the esters produced will give you a banana or bubble gum aroma. I haven't noticed any of those in my beers.

RM-MN said:

I'm hearing that the esters produced will give you a banana or bubble gum aroma. I haven't noticed any of those in my beers.

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It depends on the ester. Esters are associated with a lot of different smells in real fruits. This site has a good list:

http://www.ausetute.com.au/esters.html said:

Examples of Esters

methyl butanoate (apple)
ethyl methanoate (rum essence)
ethyl butanoate (pineapple)
pentyl ethanoate (banana)
pentyl butanoate (apricot)
octyl butanoate (orange)
methyl ethanoate (solvent)
ethyl ethanoate (solvent)

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I believe Belgian ale yeasts tend to kick off a banana flavor when fermenting at elevated temperatures (sometimes a desired feature). I wonder if other yeasts kick off different esters preferentially. Something that kicks off orange would be interesting in a Belgian wit.