Liquid yeast, beer still tastes 'green'

[Rivvo]

Apologies if this has been discussed before, I did search but couldn't see it anywhere.
I have been sampling a Patersbiere that has been bottled for about 6 weeks, I used WLP500 (Belgian Monastery) in it and it was my first use of liquid yeast. It seems to have taken a long time to clear and when I tried one last night it tasted 'green' ie too young to me (crisp green apple taste), is this a common theme with liquid yeats or is it just down to the Belgian strains, or is it just me ?
I couldn't detect any other 'off' flavours and I think it will probably be fine in the end.

[Matt12398]

Green apple tends to be acetaldehyde but if it's more cidery it can be the sign of an infection.

Liquid yeasts, in the same way as dried yeasts, usually only create off flavours if they've not been handled correctly. Did you control your fermentation temperature and if so how did you do it?

Happy 1 year Jim's anniversary by the way.

[Rivvo]

Haha cheers, I didn't even notice!
Temperature control is rudimentary but seems to work ok, it was in a room in the house with a reasonably constant temperature in winter/spring of 18' then I moved it to warmer room for a few days before cooling in the garage on a concrete floor.
It may have been the odd bottle as it wasn't full and had the last dregs of the FV in when I was bottling, reports back from a mate suggest he didn't detect the taste at all so the one I tried ladt night may have just had more yeast in it, I did try one a few weeks ago and come to think of it I don't recall getting that taste then either.
I'm pretty sure it's not infected and it was the fresh green apple taste rather than sour/vinegar like

[YeastWhisperer]

Green apple is acetaldehyde. Acetaldehyde is an organic compound that is formed during the metabolism of glucose. It gets converted to acetate and then to acetyl-CoA. Acetyl-CoA is fed into the Krebs cycle (a.k.a. the citric acid cycle) where is used for cellular energy. More often than not, the presence of acetaldehyde means that you racked too early; however, it can also be the result of serious oxidization while racking. While aging will soften the compound's impact on your beer's flavor, it will not completely eliminate it. WLP500 is Chimay's strain, which is notorious for throwing a lot of metabolic trash. WLP533 (Westmalle's strain) is far less temperamental.

[Rivvo]

Thanks for that, I must admit I am wary of oxidisation when racking/bottling but I have left myself open to hot side aeration, which I think I must have read about and completely forgotten!
I have had a second further report on the beer from someone I fore warned about the possible off tastes, he couldn't detect anything either though, it may have just been an odd bottle, I do hope so.

[Matt12398]

Fingers crossed it was limited to the ones you tried.

Hot side aeration is said to not be an issue as long as you have a strong boil. Charlie Bamforth is often misquoted as saying it doesn't exist but I believe he has shown that it whilst it can exist, the long boil counteracts the issue. Don't quote me on thst though.

[YeastWhisperer]

Green apple is not caused by HSA. The tell-tale sign of HSA is wet paper or cardboard, which is a compound known as trans-2-nonenal. Trans-2-nonenal is caused by the oxidation of lipids in the mash tun by an enzyme known as lipoxygenase. No amount of boiling will eliminate the trans-2-nonenal precursors that are formed by this enzyme.

If one examines the diagram that I posted above, one will see that ethanol can be converted to acetaldehyde. The introduction of oxygen post fermentation can trigger a metabolic phenomenon known as diauxic shift. Yeast cells can switch to using ethanol as their carbon source after they deplete all other sources of carbon that they can digest if dissolved oxygen is present.

While it is weird to think about, yeast cells consume carbon, not sugar. Sugar is little more than carbon bound to water; hence, the name carbohydrate. All of the sugars found in wort are multiples of CH20. The chemical formula for glucose is C6H12O6, which is 6 times CH20. Glucose is known as a hexose because it contains six carbon atoms. Ethanol is also a carbon-based compound with the chemical formulas CH3CH2OH, C2H5OH and C2H6O. Acetaldehyde is yet another carbon-based compound with the chemical formulas CH3CHO and C2H40. Acetaldehyde is formed via the dehydrogentation (removal of hydrogen atoms) of ethanol.

CH3CH2OH -> CH3CHO + H2

The above dehydrogenation reaction is read ethanol becomes acetaldehyde plus hydrogen gas.

[Matt12398]

I'm sorry, in this case I was not only misquoting but was also talking about the wrong thing. It was in fact a healthy fermentation, not a strong boil, should help to eliminate the effects of HSA.

Here's a bit more information quoted from another source:

"Free oxygen at 20C will remain inert (un-reactive) for days and in practical brewing situations will be removed by yeasts / absorbed by melanoidins"

[Rivvo]

My apologies I was mixing my issues! I have just discovered that I have been making an error in my process with regard to trasnferring the hot wort, however my fermentations (recent ones) have been healthy so hopefully I've headed that off.
The apple taste I think is down to the yeast as that half bottle probably had a lot more in that the average bottle.
Ps Yeastwhisperer you sure do know your stuff!

[YeastWhisperer]

I'm sorry, in this case I was not only misquoting but was also talking about the wrong thing. It was in fact a healthy fermentation, not a strong boil, should help to eliminate the effects of HSA.

Here's a bit more information quoted from another source:

"Free oxygen at 20C will remain inert (un-reactive) for days and in practical brewing situations will be removed by yeasts / absorbed by melanoidins"

That information is correct, and why one has to introduce a serious amount oxygen (O2) during racking to cause post-fermentative oxidization. However, no amount of yeast will help in the case of trans-2-nonenal, which is a major problem that limits shelf life. The hot-side oxidation reaction that causes the formation of trans-2-nonenal occurs enzymatically in the mash; hence, it does not matter if the boil scrubs O2 or the yeast cells scrub O2 because it is too late by that time. The reaction has already occurred and the precursors have already been formed.

[Matt12398]

Thanks for sharing. It's certainly provided me with an education.

[NotSure]

Sorry for reviving this thread, I brewed Worthington White Shield clone which has been in bottles for over a month now. There was a very distinct green aroma after two weeks. After five weeks the aroma is fading. The bottles are stored in the garage, the temperature is 16-18C.
Now I read conflicting advice as regards reducing acetaldehyde in beer. Some sources suggest storing beer at temps <12C, some say move the bottles to a warmer place. What should I do?

[YeastWhisperer]

I have found that bottle conditioning may reduce, but not completely eliminate acetaldehyde. The best way to eliminate acetaldehyde is by not rushing the fermentation.

[NotSure]

YeastWhisperer yes, I read your earlier post that green apples can only be reduced and not eliminated. I bottled the beer after three weeks of fermentation. For fermentation I used slurry from the secondary... I guess the acetaldehyde could have been caused by poor condition of yeast?