Author Topic: Acetaldehyde - Yeast and odor of...  (Read 1179 times)

Online rabid_dingo

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Acetaldehyde - Yeast and odor of...
« on: May 28, 2011, 09:15:25 PM »
So I brewed a mild with some smoked malt.OG if I remember correctly was about 1.044.
It sat in primary for about 6+ weeks. So I know that is is not an "unfinished" beer. After racking
it to a keg, letting that sit a week and then puting it on a line in my keggerator, I smell
green apples. Not really tasting them. The taste is defenitley percieved but it seems that
I can distinguish between tasting it and smelling it.

So, I have read that racking off the primary too soon may cause this, and that aging may help.

Is it true?

Does anyone have some specific experience with it? It sucks because I was hoping to share it next
weekend...
Ruben * Colorado :)

Offline 1vertical

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Re: Acetaldehyde - Yeast and odor of...
« Reply #1 on: May 28, 2011, 09:56:26 PM »
My experience with this was definately the taste more than the aroma. But beyond that,
It took time time time...and unfortunately, you will not be the one to say when the yeast
has gotten this cleaned up. The yeast will tell You when they are done....an unknown
time span unfortunately.
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Re: Acetaldehyde - Yeast and odor of...
« Reply #2 on: May 29, 2011, 12:19:48 AM »
Very first time I have encountered this. Oh well. I'll wait it out...

What is odd to me. I figured a couple of "Mild" "Session" beers would be
easy for me to crank out this spring.They have challenged me.  :-\
Ruben * Colorado :)

Offline 1vertical

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Re: Acetaldehyde - Yeast and odor of...
« Reply #3 on: May 29, 2011, 05:39:44 AM »
Very first time I have encountered this. Oh well. I'll wait it out...

What is odd to me. I figured a couple of "Mild" "Session" beers would be
easy for me to crank out this spring.They have challenged me.  :-\
Remember our conversation....maybe "its da water".  But it is all about
making the best environment that you can for your hard working yeasties.
A fine is a tax for doing wrong. A tax is a fine for doing well.

Offline thomasbarnes

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Re: Acetaldehyde - Yeast and odor of...
« Reply #4 on: May 29, 2011, 10:13:10 PM »
So I brewed a mild with some smoked malt.OG if I remember correctly was about 1.044. It sat in primary for about 6+ weeks.

It sounds like your yeasties stopped fermenting early, so all that extra time in the fermenter was wasted.

Some questions for you:

What yeast strain were you using? Some yeast strains produce more fermentation byproducts than others. Also, some strains are notable for flocculating before they're finished fermenting.

Did you make a yeast starter? Low yeast cell count can stress the yeast, meaning they make more acetaldehyde during the growth phase of their life cycle.

What temperature did you ferment at? Low temperatures for a particular yeast strain can also make them produce more acetaldehyde.

Did you suffer any temperature swings during the first couple of weeks for fermentation? Temperature swings can shock the yeast and make them flocc prematurely.

What percentage of adjunct sugars did you use? Anything much above 20% adjuncts doesn't give the yeast sufficient nutrient, so they produce more off-flavors.

Did you fully aerate your wort? Again, lack of oxygen in the wort can strain the yeast making them produce off-flavors.

So, I have read that racking off the primary too soon may cause this, and that aging may help.

Both of these statements are true, but they're unlikely to apply in your case. Under normal conditions, a "best mild" like you've brewed should be fully fermented in about a week and should be fully conditioned after 1-4 weeks. So, 6 weeks in primary should have been more than enough time.

Aging won't help much if the yeast has already flocculated, unless you age for a long time and let the acetaldehyde break down or oxidize into other compounds.

Does anyone have some specific experience with it? It sucks because I was hoping to share it next weekend...

I've had and seen a few batches of green apple beer. In terms of aggressiveness/danger, here are some things you can do:

1) Don't mess with it. Your yeast might have time to reduce the acetaldehyde by next week. If the green apple character is still there, live with it, or make cider from apple cores and serve it with a garnish of apple and a dash of apply syrup/concentrate.

2) Warm the beer to 65-80 F if you've been storing it cold. This might get the yeast back to work but risks speeding up oxidation of your beer.

3) If you've got any trub/yeast slurry at all in the bottom of your keg, carefully stir it back into solution. Optionally, combine this with option #2.

4) Carefully stir in 1-2 cups of fermenting wort from another batch and hope that the actively fermenting yeasts reduce the acetaldehyde without contributing off-flavors (diacetyl, more acetaldehyde).

5) Aerate your beer and hope that gets the yeasts to work.

If you go with strategies 2 or 5, drink the beer soon, since you've set the clock ticking on some really nasty oxidized character. Of course, since it's a mild, it's not going to age well at all, so you'll have to drink it quickly anyhow. Personally, I'd go with strategy #1.

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Re: Acetaldehyde - Yeast and odor of...
« Reply #5 on: May 30, 2011, 11:13:21 PM »
It sounds like your yeasties stopped fermenting early, so all that extra time in the fermenter was wasted.
Agreed
Some questions for you:

What yeast strain were you using?  Safale 05 dry yeast.

Did you make a yeast starter? I'm not in the habit of making one for a packet...

What temperature did you ferment at? 65ish without control (as in not in a fridge. Just "room" temp. where I store fermenting beer.)

Did you suffer any temperature swings during the first couple of weeks for fermentation? It may have, but none that stick out. At least no AH-HA! moment that comes to mind. Possible issue #1

What percentage of adjunct sugars did you use? Looking at my notes I have this:
5# Pale Malt
1.5# Crystal 40L
1# Flaked barley
1.25# Home Smoked MO (alderwood)
4oz Special B.
Although when looking at it via BeerSmith the only flaw is that it is too strong for a mild, fine by me...

Did you fully aerate your wort? I use a restaurant supply SS Whisk that I whirlpool for about 1 min. I have a modified hose to drain my boil kettle with that has holes in it but that is newer than this recipe.

Aging won't help much if the yeast has already flocculated, unless you age for a long time and let the acetaldehyde break down or oxidize into other compounds. Makes perfect sense...

It just solidifies my need for ferm temp control. I have a controller but currently no space for a spare fridge/freezer.
I have lucked out that here in Colorado it has stayed rather cool for Spring. I am begining to think that a spike occurred
and I don't remember one. Summer is close and I may have to shut it down for the Summer... :(
Ruben * Colorado :)

Offline thomasbarnes

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Re: Acetaldehyde - Yeast and odor of...
« Reply #6 on: May 31, 2011, 03:16:00 AM »
What yeast strain were you using?  Safale 05 dry yeast.

That's a very clean strain, and it sounds like you did everything right regarding starter and fermenting temperature. The fermentation temperature might have risen a bit, but probably not to levels where off-flavors were that much of a problem. Anyhow, acetaldehyde isn't generally associated with high temperature fermentation.

It's just possible that you overpitched. The dry yeast packets have a lot of cells and your mild wasn't that big a beer. On the other hand, if the packet was old and you didn't rehydrate the yeast first, it's possible that your cell count was too low. Either case can result in off-flavors.

The recipe looks solid, so no problems there. Actually, for an authentic mild, you could have used a bit of caramelized sugar or syrup, but since you added the smoke malt I can tell you're not a slave to style categories. BTW, while it's not recognized by the BJCP, mild ale actually comes in different strengths. Remove the smoked malt and you've got what the Brits would call a "best mild" or "strong mild" which overlaps into English brown ale or brown porter territory. (Mild is often the draught product, brown ale the bottled product. Take the beer a bit darker and roastier, and it's a brown porter.) Keep the smoke in, and you've potentially got something that would taste like an authentic 17th or 18th century "brown beer" or "running porter."

[/b]Did you fully aerate your wort? I use a restaurant supply SS Whisk that I whirlpool for about 1 min. I have a modified hose to drain my boil kettle with that has holes in it but that is newer than this recipe.

This is a potential problem. If you're getting oxygen into your wort by stirring or agitating, you need to aerate for at least 10 minutes to get anything like the oxygen levels you need (about 6 ppm max. using just air). To get proper O2 levels in a strong wort you almost need to use oxygen and a sintered airstone to get your magic 10 ppm dissolved O2. I can't comment on O2 levels achieved using an aerating cane/hose since I've never used one.

It just solidifies my need for ferm temp control. I have a controller but currently no space for a spare fridge/freezer.
I have lucked out that here in Colorado it has stayed rather cool for Spring. I am begining to think that a spike occurred
and I don't remember one.

Sympathy. I'm stuck with the same problem. But, I don't think that a temperature spike would have made the yeast flocc prematurely. Instead, it's more likely a temperature crash that knocked them out of solution. A potential situation for this to occur might be a hard cold snap for a couple of days, coupled with serious drafts through your fermenting area.

Alternately, the fermentation temperature started unusually high or slow so the yeast were under stress or otherwise produced lots of off flavors, then went cooler so that they didn't have time scavenge up the acetaldehyde and diacetyl they produced.

Speaking of which, did you get any buttery or slick notes in your beer, or are you not particularly sensitive to diacetyl?

The combo of "green apple and butter" would make it a slam dunk case for a fermentation problem, whereas acetaldehyde aroma on its own might be due to some other things.

Since you've got a draught system, it couldn't hurt to clean your lines, especially if you're getting off-flavors from your other beers. Some bacteria will produce acetaldehyde plus other off-flavors and they love to live in dirty beer lines.

Finally, it's also possible that you're just mistaking apple esters, which are really common in ales, for acetaldehyde, so there's actually no problem. Sometimes apple esters plus a bit of roast can be interpreted as acetaldehyde. The smoke malt might be tricking your sense of smell/taste.

Offline 1vertical

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Re: Acetaldehyde - Yeast and odor of...
« Reply #7 on: May 31, 2011, 07:00:29 AM »
[/b]Did you fully aerate your wort? I use a restaurant supply SS Whisk that I whirlpool for about 1 min. I have a modified hose to drain my boil kettle with that has holes in it but that is newer than this recipe.

This is a potential problem. If you're getting oxygen into your wort by stirring or agitating, you need to aerate for at least 10 minutes to get anything like the oxygen levels you need (about 6 ppm max. using just air). To get proper O2 levels in a strong wort you almost need to use oxygen and a sintered airstone to get your magic 10 ppm dissolved O2. I can't comment on O2 levels achieved using an aerating cane/hose since I've never used one.

Ruben this is the one I spoke about really the "better" mousetrap...

http://www.williamsbrewing.com/22-AERATION-WAND-P490C106.aspx
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Offline denny

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Re: Acetaldehyde - Yeast and odor of...
« Reply #8 on: May 31, 2011, 08:35:56 AM »
Keep in mind that with dry yeast the need for aeration is drastically reduced.
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Re: Acetaldehyde - Yeast and odor of...
« Reply #9 on: May 31, 2011, 10:33:14 AM »
Speaking of which, did you get any buttery or slick notes in your beer, or are you not particularly sensitive to diacetyl?
I can't say I am sensitive to diacetyl, I can't specifically say I have ever tasted it no slick notes to mention..

The combo of "green apple and butter" would make it a slam dunk case for a fermentation problem, whereas acetaldehyde aroma on its own might be due to some other things. <- this is the exact situation. I smell it, it is strong but really don't taste it. The hops and the smoke are there the smoke is milder than I expected.

Since you've got a draught system, it couldn't hurt to clean your lines, especially if you're getting off-flavors from your other beers. Some bacteria will produce acetaldehyde plus other off-flavors and they love to live in dirty beer lines. I just got done cleaning the keg lines. One keg of PBW under pressure pushing the solution through for a bit then let the solution sit, about 10-15 min, then run StarSan solution run through and do the same. I run the StarSan through for a longer period as a rinse as well.

Finally, it's also possible that you're just mistaking apple esters, which are really common in ales, for acetaldehyde, so there's actually no problem. Sometimes apple esters plus a bit of roast can be interpreted as acetaldehyde. The smoke malt might be tricking your sense of smell/taste. <-Possibility. First time that I have let the smoke be part of a recipe that is simple compared to other recipes...

Thanks Thomas, good points to consider.
Keep in mind that with dry yeast the need for aeration is drastically reduced.
I always understood this to be the case. Especially from the old olive oil thread. So I figure my efforts, muted my most
standards, were complementary to the already ready yeast...


Ruben * Colorado :)

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Re: Acetaldehyde - Yeast and odor of...
« Reply #10 on: June 04, 2011, 12:15:24 PM »
I'm currently having this problem with an AG SMASH kolsch and wlp0029. Vigorous but lengthy fermentation at 62F and 5 weeks in the fermenter. I've had this occur before at this temp with other ale strains like wlp02. Interesting thing is this has been a side by side with an extract batch and that has turned out pretty awesome with no off flavors.

In my case the flavor is closer to "melon" which I find disgusting in beer. It's not grassy or vegetal to me but I'm wondering if the cause is poorly stored malt? My sack is easily 4+ months old and has set in the garage with all it's temp swings.

Usually acetaldehyde goes away with time but this time it hasn't. So I dry-hopped the keg with 1oz of Zeus and crossed my fingers. ;)
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Offline dmtaylor

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Re: Acetaldehyde - Yeast and odor of...
« Reply #11 on: June 05, 2011, 05:53:46 AM »
I recently read that pure acetaldehyde boils at 68 F, so I'm recommending to anyone who thinks they've got it, to warm up the beer for a few days and see if it helps with offgassing it.  In theory, it should work!
Dave

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