Hunting the dreaded off-flavour.... marzipan.

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Miraculix

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Good evening,

There is this one off flavour that shows up in all of my last brews. It is a hint of marzipan/maybe almond-ish. Hard to describe, it overshadows the malt character. Sometimes it is stronger, sometimes it is less pronounced, but it seems to be always present in my last brews. I had this ocassionally back in britain as well, so I tried multiple things:

1st thought: Almond? Oxidation of amino acids! Get rid of the thin walled pot on your gas stove, and get a thick walled one, you are scorching the wort when boiling in that thin walled thing..... Did that, was not the reason.

2nd thought: Ok, so it must be the fact that I always have this cloudy wort in the kettle, because I brew in a bag. These cloudy substances must be rich in amino acids and whatnots, so these are clearly being oxidised while boiling. I have to change to a lautering system, get clear wort, job done! ... did that and ... nope.... I even managed to brew my strongest marzipan flavoured beer with that new system, my Marzipan AK,..... different storry.

3rd thought: OK, it really needs to be the malt then. I brew always with british pale malts, maybe that is a trait of these british malts? ..... what shall I say... nope! Brewed something with German pilsener, munich and a bit of wheat, tadaaaa, hint of marzipan.

4th thought: Infection!.... nope. Nothing wrong with the beers i have brewed (except for the marzipan), I had infected batches in between, back in the days... funny enough, these did not taste like marzipan :D

5th thought: Something strange during mashout maybe? Maybe temperature is too high? I have to try a single infusion 63C° mash. ...did that, did not help. Seems to make good beer though, I might ditch the multi step stuff in the future... again, different storry.

6th thought I even tried to remove the oxygen from the water I am using by adding yeast and a bit of sugar the day before brewing... nope.

7th thought of the day: OK, oxidation somewhere.... but where? When Vorlauf is running, I have this bubble within the tubing, that all the liquid passes by, so the tubing is actually aerating all my wort. I do not know if this one bubble in the tubing is enough? Shouldn't that oxygen within this bubble be used up fairly quickly? I mean, all my wort passes through this tubing when lautering.... uh... I got an Idea. Maybe I can remove the air by first brining the silicon hose up above water level, and then down again. A bit like siphoning it. I will try to do this... although the tube is a bit short... but anyway, that could work.

But would'nt everybody who is lautering throw a silicon hose by gravity actually have this marzipan problem then?


Any other ideas?

This off-flavour was not always there, back in the UK it showed up irregularly, I was doing BIAB back then. Now it is almost every brew in varying strengths. From just a tiny hint to liquid marzipan without sugar, all there.
On the other hand, it might be that my tastebuds learned how to detect it and just did not detect it as an off flavour back then.... I could stick to stouts from now on, it does not show up there, or it is covered by the roast.
Haha.

Solution? Anybody?

haaaaaalp!

Edit: 8th thought: could it be actual cooked corn flavour that I'm interpreting as almond-ish? Maybe I'm not bottling long enough? All my last brews were actually boiled for maximum 30 minutes, some of them even less. Also not what I would call a strong rolling boil, more like a gently bubbling boil. Could that be it?
 
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hottpeper13

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What about stressed yeast or maybe too much yeast nute? Do you get the flavor before or after fermentation. I taste my beers at all stages.
Something new in the water. Are you using a new cleaner? Repasivate all your stainless.
 
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Miraculix

Miraculix

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What about stressed yeast or maybe too much yeast nute? Do you get the flavor before or after fermentation. I taste my beers at all stages.
Something new in the water. Are you using a new cleaner? Repasivate all your stainless.
Nope and nope. Nothing new, no yeast nutrients, no new cleaner..... Only thing is that my boils got shorter and that I switched to a full volume sparge system, gravity based, instead of the biab. I wouldn't attribute this particular taste to yeast stress, I think we can rule that one out. It happens at all kind of pitching rates with dry and with liquid yeasts.
 

TheMadKing

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@Miraculix Could you also possibly describe the flavor as stone fruit such as cherries?

I get a stone fruit flavor (that I could see being called marzipan) in beers with lots of crystal 60-80 malt OR in beers where I have accidentally or intentionally caused some kettle Caramelization OR in beers where I use brewers invert #3. In short I believe it's the result of complex sugars in your beer. I just had a stone fruit bomb Scottish ale that was high in Crystal 60 and fermented with LA3

How hard are you boiling?.. Edit nevermind you answered this sorry!

Any ingredients in common in all these beers that might be introducing complex sugar?

Another possibility is yeast esters too. So it could be the yeast choices (British strains?) and/or fermentation temp.
 
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Miraculix

Miraculix

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@Miraculix Could you also possibly describe the flavor as stone fruit such as cherries?

I get a stone fruit flavor (that I could see being called marzipan) in beers with lots of crystal 60-80 malt OR in beers where I have accidentally or intentionally caused some kettle Caramelization OR in beers where I use brewers invert #3. In short I believe it's the result of complex sugars in your beer. I just had a stone fruit bomb Scottish ale that was high in Crystal 60 and fermented with LA3

How hard are you boiling?

Any ingredients in common in all these beers that might be introducing complex sugar?

Another possibility is yeast esters too. So it could be the yeast choices (British strains?) and/or fermentation temp.
Actually, the less I use any malt that has a very strong flavour, the easier this almond-ish of flavour is recognised. There is no common malt within these beers unfortunately. First I was attributing it to o oats, then to British mo malt, but at the end I was able to rule them out. The paler the beer the more likely it isto appear it seems. Maybe it is the short boil after all? DMS?

Yeast esters was also an idea I've followed, but it is really pooping up independently from yeast strains... Us 05, verdant IPA, 3470... Just to name a few.

What really gets me is that I brewed beers completely without this flavour and I cannot tell you how!
 

Beernik

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You seem to have been looking at a lot of pre-boil oxidation paths. Have you looked at rescuing post fermentation oxidation?
 

TheMadKing

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Actually, the less I use any malt that has a very strong flavour, the easier this almond-ish of flavour is recognised. There is no common malt within these beers unfortunately. First I was attributing it to o oats, then to British mo malt, but at the end I was able to rule them out. The paler the beer the more likely it isto appear it seems. Maybe it is the short boil after all? DMS?

Yeast esters was also an idea I've followed, but it is really pooping up independently from yeast strains... Us 05, verdant IPA, 3470... Just to name a few.

What really gets me is that I brewed beers completely without this flavour and I cannot tell you how!
Hmm that's a conundrum

Do you taste it when you just chew whole barley malt?

A suggestion for troubleshooting (and you may have already tried this) is to taste your wort throughout the entire process and see where you can start to pick it up. If it's only in the bottles it may have something to do with how you are cleaning prepping bottles or caps?

You could try buying a small pony keg of commercial beer and repackaging it in bottles to see if you can taste it there. That woild definitely point to something in your bottling

Do you taste it in any commercial beers?
 

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1) Can you describe your bottling/ bottle conditioning process? and 2) do you cold storage after or no?
 

AlexKay

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A little web sleuthing comes back with benzaldehyde as a likely culprit. If this is really driving you crazy, maybe purchase some food-grade benzaldehyde to see if that's it?
 
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Miraculix

Miraculix

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You seem to have been looking at a lot of pre-boil oxidation paths. Have you looked at rescuing post fermentation oxidation?
I think (emphasize on think, does not mean that it is correct), that my fermenter ist really air tight, so there should not be anything happening in there, I also usually bottle after 10-14 days. Bottling happens through a bottling wand and I leave very little headspace in the bottle, hop aroma and flavour last remarkably long that way, so I think we can rule out oxidation in the bottle as a likely reason.

Hmm that's a conundrum

Do you taste it when you just chew whole barley malt?

A suggestion for troubleshooting (and you may have already tried this) is to taste your wort throughout the entire process and see where you can start to pick it up. If it's only in the bottles it may have something to do with how you are cleaning prepping bottles or caps?

You could try buying a small pony keg of commercial beer and repackaging it in bottles to see if you can taste it there. That woild definitely point to something in your bottling

Do you taste it in any commercial beers?
Yep, exactly what I also thought and what I am doing, tasting throughout the whole process. I cannot find this taste within the freshly boiled wort, or before boiling. BUT the wort obviously tastes much stronger anyway and to be completely honest, I have not looked for it specifically. In hinsight, I obviously should have done that. Thanks for reminding me.

The first time I taste this off-flavour is always in the hydrometer sample after fermentation. Green beer.

The really wired thing is though, sometimes, it even seems to fade away over time (like a month in the bottle or something like that). A week more in the fermenter does not change a thing though, so it does not seem to be a "yeast does not have time to clean up" issue.

I have never tasted this taste in a commercial beer. Although the re-bottling idea sounds like a good idea, I think, as this flavour is already present directly after fermentation, I luckily do not have to go through that hustle :D.


1) Can you describe your bottling/ bottle conditioning process? and 2) do you cold storage after or no?
See above, bottling and, little headspace, air tight fermenter. I should have mentioned that earlier, the flavour is already there, when the beer comes out of the fermenter...

A little web sleuthing comes back with benzaldehyde as a likely culprit. If this is really driving you crazy, maybe purchase some food-grade benzaldehyde to see if that's it?
Thank you, I will google that and see what that might bring up.
 
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Miraculix

Miraculix

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A little web sleuthing comes back with benzaldehyde as a likely culprit. If this is really driving you crazy, maybe purchase some food-grade benzaldehyde to see if that's it?
Ok, googled it and this is basically what I also came up with before and why I have thought about oxidation (could have said this before actually...). If it is hot side oxidation, it might be from the long tube that my wort runs through when doing the Vorlauf, basically from normal table height into a bowl on the ground. When Vorlauf is done, Lautering happens through the same tubing, same height but obviously into the kettle, which stands on the ground instead of the bowl.

There is always air in the tubing, so the wort actually gets kind of aerrated before boiling.

How can I get the Lautering going, without buying a pump and without aerating the ish out of the wort while using gravity to lauter?
 

TheMadKing

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You taste it in green beer?

Have you done a forced diacetyl test? I'm very insensitive to diacetyl and I could easily see it being called marzapan

You could be having a diacetyl issue
 
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Miraculix

Miraculix

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You taste it in green beer?

Have you done a forced diacetyl test? I'm very insensitive to diacetyl and I could easily see it being called marzapan

You could be having a diacetyl issue
No I did not. How do I do it? ... ok ok... I google it :D

Thanks!

Edit: If anybody should have the same question....
 
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Miraculix

Miraculix

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You taste it in green beer?

Have you done a forced diacetyl test? I'm very insensitive to diacetyl and I could easily see it being called marzapan

You could be having a diacetyl issue
Diacetyl is this buttery taste, right? No that is not it... I know how this tastes like, had one beer which was pure butter for me (a big name beer in a brewdog pub, btw. I think it was a cloudwater lager, if I remember correctly).....
 

TheMadKing

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So I found this thread where some dude had a similar problem 3 years ago 😉


Two things pop out to me between the two threads.. Have you ever had your water tested? And does your water taste like anything?

Second, can you describe your EXACT cleaning regimine including cleaners, contact times, and rinsing procedure?
 

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It could very well be heat stress. Not from scorching but just too long a boil at too high an intensity. Homebrew lore has us believe that roiling volcanic cauldrons are necessary to drive off DMS but that really that isn't the case. A nice gentle partially covered low boil, limiting the evaporation to 10% or less is all that is required. I don't think it's oxidation related.

Just trying to help.
 
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Miraculix

Miraculix

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So I found this thread where some dude had a similar problem 3 years ago 😉


Two things pop out to me between the two threads.. Have you ever had your water tested? And does your water taste like anything?

Second, can you describe your EXACT cleaning regimine including cleaners, contact times, and rinsing procedure?
Well, this guy that you discovered there was living in UK at that time, so the water cannot be the reason as he is now living in Germanz and facing almost the same issues, though now it is in almost every beer. In the Uk it was not in every beer.... The water actually is fine here. In the Uk, I used bottled water.

It could very well be heat stress. Not from scorching but just too long a boil at too high an intensity. Homebrew lore has us believe that roiling volcanic cauldrons are necessary to drive off DMS but that really that isn't the case. A nice gentle partially covered low boil, limiting the evaporation to 10% or less is all that is required. I don't think it's oxidation related.

Just trying to help.
I think so too, but I realy boil shortly and I boil very gently... literally only 20-30 minuts.
 

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I know you don’t like information from books written by old dead Germans however Kunze gives us some interesting clues here:

3.4.1.6 Thermal exposure of the wort
During boiling, further Maillard products and Strecker aldehydes are formed, tannins oxidized and thus the the thermal exposure of the wort is further increased.

And here we find in this paper..
Impact of Wort Amino Acids on Beer Flavour:
Inês M. Ferreira and Luís F. Guido

these descriptions of the compounds in question.

Strecker Degradation Products
2-methylpropanal - Grainy, varnish, fruity
2-methylbutanal - Almond, apple-like, malty
3-methylbutanal - Malty, chocolate, cherry, almond
Methional - Cooked potatoes, worty
Phenylacetaldehyde - Hyacinth, flowery, roses
Benzaldehyde - Almond, cherry, stone

It certainly looks like the smoking gun.

What percent of the initial volume do you lose during the boil?
 
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Miraculix

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I know you don’t like information from books written by old dead Germans however Kunze gives us some interesting clues here:

3.4.1.6 Thermal exposure of the wort
During boiling, further Maillard products and Strecker aldehydes are formed, tannins oxidized and thus the the thermal exposure of the wort is further increased.

And here we find in this paper..
Impact of Wort Amino Acids on Beer Flavour:
Inês M. Ferreira and Luís F. Guido

these descriptions of the compounds in question.

Strecker Degradation Products
2-methylpropanal - Grainy, varnish, fruity
2-methylbutanal - Almond, apple-like, malty
3-methylbutanal - Malty, chocolate, cherry, almond
Methional - Cooked potatoes, worty
Phenylacetaldehyde - Hyacinth, flowery, roses
Benzaldehyde - Almond, cherry, stone

It certainly looks like the smoking gun.

What percent of the initial volume do you lose during the boil?
Yes, I think so as well, it is more about how to avoid this in the future right now. I think the main problem is probably the lautering and the Vorlauf which kind of aerates the wort pre-boil and at mashing temperatures due to it's current design. I am now wondering how people who do the Vorlauf and the Lauter via gravity, do this without much air in the hoses/pipes/whatever they get the liquid out through.
 
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monkeymath

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Marzipan sounds pretty good to me, so I'm curious to see this resolved :D
I remember having a homebrewed Kveik "Kölsch" a while back that tasted distinctly of marzipan. It was pretty good.
 

Bilsch

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Yes, I think so as well, it is more about how to avoid this in the future right now. I think the main problem is probably the lautering and the Vorlauf which kind of aerates the wort pre-boil and at mashing temperatures due to it's current design. I am now wondering how people who do the Vorlauf and the Lauter via gravity, do this without much air in the hoses/pipes/whatever they get the liquid out thorugh.
Careful my friend.. a couple of your posts in this thread have come dangerously close to Lodo talk and you know what they do here to people who utter those words.
 
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Miraculix

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Careful my friend.. a couple of your posts in this thread have come dangerously close to Lodo talk and you know what they do here to people who utter those words.
That's actually the thing, I don't care if something is considered by somebody lodo or not, I just want things to work while not doing more than necessary for it. I mean come on, it's like 90% chance here that hot side oxidation is happening and causing the issues.
 
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Miraculix

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About the lautering process, I do it the same way, and have never had any issues with marsipan or almondy off-flavours. Just my 2 cents.
Thanks that's good to hear! How are you boiling? How long? Heat source? Gentle or full rolling boil?
 

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That's actually the thing, I don't care if something is considered by somebody lodo or not, I just want things to work while not doing more than necessary for it. I mean come on, it's like 90% chance here that hot side oxidation is happening and causing the issues.
I’m pleased we can have this conversation about any and all brewing techniques.

That being said, Ive never experienced the off flavor you have described in all my hido days and certainly not after. Additionally amongst the other group no one has mentioned it either. Oxidized precursors are required for the Strecker degradation but usually also heat to complete. Is it possible that your mash is introducing heat stress through the mechanical heating or just running too long at too high of temperatures?

If you want to try and limit the oxygen in your mash we can certainly help you with the easiest and best ways to accomplish that.
 
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Miraculix

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Usually 90 min, portable 2000W induction heat pad from IKEA. My boils are not that intense, more of a hard simmer than full on boil.
Ok, thanks. Do you also have this air trapped in the tubing when lautering, which kind of aerates the wort?



So I got basically two possible reasons with different solutions:

Number one, I'm mistaken DMS (cooked corn) for some almond-ish taste and it is there because my boil is too short and too weak.

Number two, hot side oxidation of maillard products. I will try do fix that lautering problem somehow.... Maybe if i squeeze the end of the silicon tubing together with s wire to limit the flow rate at the end, maybe it will then stay equally full without any air being trapped in there.
 

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Have you made any raw beer recently? Wonder if you could detect it in a no boil.
 
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Have you made any raw beer recently? Wonder if you could detect it in a no boil.
I was thinking about it as well! My last raw beer was years ago, but I cannot remember tasting anything almond-ish there. Maybe I will brew an english raw bitter next, just to see.

I usually get a bit of air in the tubing when I drain of from the lautering bucket to the BK. But I think none but the most hardcore LODO-ists would argue that it would have that much of an impact. Have you tried boiling longer?
I think I did try boiling longer back in the Uk, but I do not know for sure.

I’m pleased we can have this conversation about any and all brewing techniques.

That being said, Ive never experienced the off flavor you have described in all my hido days and certainly not after. Additionally amongst the other group no one has mentioned it either. Oxidized precursors are required for the Strecker degradation but usually also heat to complete. Is it possible that your mash is introducing heat stress through the mechanical heating or just running too long at too high of temperatures?

If you want to try and limit the oxygen in your mash we can certainly help you with the easiest and best ways to accomplish that.
I thought so as well, that´s one of the reasons I ditched the biab system with which I was heating the whole thing in a pot on the stove while stirring, to reach the different temperature steps. I though uneven heat distribution, maillard reactions, oxidation.... But it did not solve the issue as I am facing the same off flavour now with a Full volume single infusion mash with normal Vorlauf/lauter system. So no way for heat induced stress, just 65 C mash in and from there, no more heat till the boil kettle (did this intentionally with my last batch, I usually at least mash out).

I also do not think that it actually is the mash. I once or twice deoxigenated my water with the baking yeast plus a bit of sugar and one day waiting trick, did not do anything detactably good or bad.

I am really wondering if this Vorlauf/Lauter silicon hose is the culprit. The hose is never even partially full with wort when running the wort through it, so there is about 1.0 m long silicon hose through which the wort runs and mixs with the air all the time due to internal turbulences.

But on the other hand, why did I also have this issue with biab back then? Not as often as now, but still, it was there.
 

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I am really wondering if this Vorlauf/Lauter silicon hose is the culprit. The hose is never even partially full with wort when running the wort through it, so there is about 1.0 m long silicon hose through which the wort runs and mixs with the air all the time due to internal turbulences.
This setup does sound like a good way to oxidize the wort at least to a certain degree. And of course you already know the hotter wort, the faster these reactions proceed. If you give it heat, surface area and an exchange of air it will be happening. Silicone is also particularly highly permeable to oxygen so that is not helping the situation either.

It is curious you get this since are plenty of mashes being very well aerated by brewers on this forum each and every day followed by intense boils. So you'd think someone else would have run into this marzipan flavor by now.

Two more points to ponder.. everyone is unique in their sensitivity to different compounds. Is it possible that you are just particularly attune to this one? I have also noticed as the years have gone by and my brewing skills improve, I'm able to reduce or eliminate some flaws in my beers which allows others jump forward that were always there but hidden under poor attenuation, yeast esters, herbstoff, husk astringency et. al. Is it possible that you have upped your game and thus uncovered things you never knew were always there?
 

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I also do not think that it actually is the mash. I once or twice deoxigenated my water with the baking yeast plus a bit of sugar and one day waiting trick, did not do anything detactably good or bad.
I just wanted to address this for a moment.
Removing the oxygen from the strike water is a good first step toward reducing HSA but really is only a small drop in the bucket if further protections aren't also put in place. Your water, depending on the temperature, probably contains about 4-5ppm dissolved oxygen. Then you add the grain with stirring and you have quickly added that amount back plus some, so simply de-aerating the strike water ends up doing nothing. There are two ways for us at the homebrew scale to provide the further protection, the first being inert gas purging the grain and the second to add active oxygen scavengers to the strike water. Commercial breweries don't need to do either because they have expensive wet mills and or vormaischers that get around these problems we are stuck with. Also scale of their kettles is a big advantage.

Note: If anyone is interested in the technology mentioned above, see this patent for one example: DE202013100550U1 - Shot and mash device - Google Patents

P.S. I always wonder about that yeast method for de-aeration.. I hear the guy that came up with that is kinda shifty.
 
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This setup does sound like a good way to oxidize the wort at least to a certain degree. And of course you already know the hotter wort, the faster these reactions proceed. If you give it heat, surface area and an exchange of air it will be happening. Silicone is also particularly highly permeable to oxygen so that is not helping the situation either.

It is curious you get this since are plenty of mashes being very well aerated by brewers on this forum each and every day followed by intense boils. So you'd think someone else would have run into this marzipan flavor by now.

Two more points to ponder.. everyone is unique in their sensitivity to different compounds. Is it possible that you are just particularly attune to this one? I have also noticed as the years have gone by and my brewing skills improve, I'm able to reduce or eliminate some flaws in my beers which allows others jump forward that were always there but hidden under poor attenuation, yeast esters, herbstoff, husk astringency et. al. Is it possible that you have upped your game and thus uncovered things you never knew were always there?
Exactly my thoughts, especially why I seem to be the only one and the following reasoning. It might be that my taste evolved, it might also be that I am overly sensitive for this particular off flavour. I know of other guys who are, for example, overly sensitive for diacethyl, they taste it even in most commercial beers. I cannot rule that one out unless I get somehow a sample which has this off flavour causing substance, but underneath the normal taste threshhold. If I would taste it, riddle solved.

What I don´t think is that my process evolved so significantly, that this one off-flavour is now uncovered. My process did evolve a bit, but not that much. I managed to brew the perfect beer once with this process (really, it was just perfect, everybody who had it agreed, the perfect english bitter, I never managed to brew it again, recipe is Miraculix Best in the ale forum) and I managed to brew Seargent Nutty, The King Of The Almonds with it as well :D

Now I changed parts of the system but same storry (except for the perfect beer, unfortunately).

I just wanted to address this for a moment.
Removing the oxygen from the strike water is a good first step toward reducing HSA but really is only a small drop in the bucket if further protections aren't also put in place. Your water, depending on the temperature, probably contains about 4-5ppm dissolved oxygen. Then you add the grain with stirring and you have quickly added that amount back plus some, so simply de-aerating the strike water ends up doing nothing. There are two ways for us at the homebrew scale to provide the further protection, the first being inert gas purging the grain and the second to add active oxygen scavengers to the strike water. Commercial breweries don't need to do either because they have expensive wet mills and or vormaischers that get around these problems we are stuck with. Also scale of their kettles is a big advantage.

Note: If anyone is interested in the technology mentioned above, see this patent for one example: DE202013100550U1 - Shot and mash device - Google Patents

P.S. I always wonder about that yeast method for de-aeration.. I hear the guy that came up with that is kinda shifty.
That is basically a mix of assumptions here. I certainly introduce oxygen during the mash in (I have the grain in the mash bucket and fill it up with hot water, so not as bad as stirring the grain in, more like a wrathfull underletting. Afterwards it gets stirred). But how much oxygen is introduced is a bit of a guess and how much it matters at this temperature is also a bit of a guess. Oxygen dissolves differently in heated water, but do not ask me how it actually affects the oxygen/time being dissolved. Usually gasses dissolve better in cooler liquids and if I think how long the small headpsace of a filled bottle needs to get its oxygen into the liquid (weeks), I am tempted to say that the little oxygen I introduce during mashing, cannot be the reason for this off flavour. But this is obviously an assumption as well.
 

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A little web sleuthing comes back with benzaldehyde as a likely culprit. If this is really driving you crazy, maybe purchase some food-grade benzaldehyde to see if that's it?
That's the first thing that jump at at me. Oxidation of malt compounds causes an "almond" or marzipan flavor. It's likely post-fermentation oxidation.
 
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That's the first thing that jump at at me. Oxidation of malt compounds causes an "almond" or marzipan flavor. It's likely post-fermentation oxidation.
Post fermentation is unlikely, as it is the strongest directly after fermentation finished. The hydrometer sample when bottling is always the strongest example of this off flavour. If it is not extremely strong (differs from beer to beer), sometimes it even fades with time, sometimes it fully disappears. Sometimes it just gets less pronounced with time. My marzipan AK for example, still tastes like marzipan, even after half a year in the bottle... but not as strong as it was before the aging.
 
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OK I had another idea. How about that:

The question for me is, why I sometimes had it in the UK, not everytime though, and now have it with a different system in Germany as well.

I might found out why. In the UK I used to do no chill biab. I also used to throw the hot wort directly out of the kettle into the fermenter, to heat sanitise the fermenter. I airlocked it and let it cool over night. I obviously introduced lots of oxygen during the "transfer" (literally just dumping it from kettle into fermenter) and after that it stayed hot for long time. Meaning oxygen and elevated temperatures were both present for hours. Also, more proteins in the wort because I used to dump all in, trub and all.

It might be that I did not introduce as much oxygen with biab as I am doing now with the faulty vorlauf/lauter, but dumping the liquid and then no chill seem to tick the boxes for possible oxidation as it had that much more time to oxidise.

With the faulty vorlauf/lauter and chill system, I introduce the oxygen pre boil and probably much more then with the biab system. So the shorter time the wort is heated might be enough here because of the extra dose of oxygen.

In the meantime, I got myself a wort chiller. So next beer will be biab again, but with a chilled wort, no excessive splashing and single infusion. I will use the yeast method to rid the water of O2, just because I can.

If this works, we narrowed it down to the lauter/vorlauf aeration.
 
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I seem to be dong a similar method to you. The only difference would be i use a cube and fill it to the top. What a pita, i hope you manage to resolve it.
 
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I seem to be dong a similar method to you. The only difference would be i use a cube and fill it to the top. What a pita, i hope you manage to resolve it.
Which one do you mean? The biab method? How long are you boiling your wort?
 
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