stoutaholic
Well-Known Member
I've brewed a about 35 batches, everything from Belgian Dark Strongs to American Lagers to Scottish Ales, and have had success with every style except high-gravity lagers. Of the 5 high-gravity lagers I have brewed, all have contained a distinct acetaldehyde character; that is to say, an acetic-cider, or green-apple type character, with the attendent astringency.
None of my other beers have ever had this character; in fact, my medium-gravity lagers, such as my Munich Dunkel, German Pilsner, and Oktoberfest, have all won medals. So I don't have a generalized problem with brewing beer or lagers. This is not a sanitation issue; it is not lactic acid that I am tasting, and it wouldn't make sense for ONLY the high-gravity lagers to become contaminated (fermentation starts as quickly as my other lagers).
So I am really struggling to understand what I am doing wrong. I have read that acetaldehyde can be due to over-pitching and over-oxygenation, and I am pitching at the upper range of the guidelines, but somehow this over-pitching and over-oxygenation (if that is the problem) only manifests itself in high-gravity lagers, because I pitch and oxygenate my regular gravity lagers in exactly the same fashion.
My technique, for all lagers, is to pitch at about 1.5 million cells per mL per degree Plato. So, for 6 gallons of a 1.070 Bock, that would mean pitching about 581 billion cells. I have obtained this pitching level in various ways for the different batches; either by creating a large continuously aerated starter (using Mr. Malty's pitching rate calculator) or by directly pitching 6 - 7 Wyeast Activator packs (depending on the calculated viability of those packs, based upon their packaging date), or by a combination of a starter and direct pitching. Actual pitching rates have probably varied between 1.45 and 1.9 million cells per mL Plato, due to the impreciseness of viability and starter growth calculations.
My oxygenation procedure uses a standard disposable oxygen tank (the red kind from the hardware store) and a regulator attached to a 2 micron stone. Prior to pitching, I open up the regulator all the way and oxygenate for 1 - 2 minutes. Tests with my dissolved oxygen meter have indicated that this provides about 14 - 17 ppm of oxygen.
So, according to what I have read of the brewing literature, these pitching and oxygenation rates SHOULD be ideal. And they work wonderfully for my normal gravity lagers.
I pitch at 46 - 48 F and allow the temperature to rise to 48 or 50 F during fermentation.
Exposure of the beer to oxygen after ethanol has been produced can also produce high acetaldehyde levels, as ethanol can be re-oxidized to acetaldehyde and acetic acid. However, this cannot be the issue because I am using a sealed stainless conical fermenter and actually draining the wort (instead of siphoning) directly into a CO2 purged keg. The keg is purged by filling with sanitizer and blowing it all out with CO2.
Another possibility would be that I am separating the beer from the yeast too soon, or crash cooling before fermentation has finished, or something of that nature. However, I typically raise fermentation temps to 55 - 58 F once the ferment has reached 2 points of final gravity (as measured by a hydrometer, not by the bubbling of an airlock or guestimation) and hold that temp for a week before cooling.
Long warm conditioning is also supposed to reduce acetaldehyde. So I tried letting these beers sit at about 65 F for 3 weeks after the end of fermentation. Though the acetaldehyde character was somewhat reduced by this conditioning, it was still very present. I even tried initiating a secondary fermentation by adding corn sugar to the keg and allowing it to completely ferment out. I've also tried krausening. My hope was that the re-activated yeast would then convert the acetaldehyde. Again, no luck.
Could this character be something else other than acetaldehyde? If so, what compound would make sense? And why would this character reliably show up in every high-gravity lager I have brewed, but in none of the other 25 batches? Apart from this acetaldehyde character, the beers have no other off-flavors, as would be expected in the case of contamination. It is an unmistakably appley, acetic character that is very apparent in the aroma and first few sips, but then becomes less noticeable (but still apparent) as you continue drinking the beer. My wife had the same impression; she assumed I was trying to brew an apple beer.
None of my other beers have ever had this character; in fact, my medium-gravity lagers, such as my Munich Dunkel, German Pilsner, and Oktoberfest, have all won medals. So I don't have a generalized problem with brewing beer or lagers. This is not a sanitation issue; it is not lactic acid that I am tasting, and it wouldn't make sense for ONLY the high-gravity lagers to become contaminated (fermentation starts as quickly as my other lagers).
So I am really struggling to understand what I am doing wrong. I have read that acetaldehyde can be due to over-pitching and over-oxygenation, and I am pitching at the upper range of the guidelines, but somehow this over-pitching and over-oxygenation (if that is the problem) only manifests itself in high-gravity lagers, because I pitch and oxygenate my regular gravity lagers in exactly the same fashion.
My technique, for all lagers, is to pitch at about 1.5 million cells per mL per degree Plato. So, for 6 gallons of a 1.070 Bock, that would mean pitching about 581 billion cells. I have obtained this pitching level in various ways for the different batches; either by creating a large continuously aerated starter (using Mr. Malty's pitching rate calculator) or by directly pitching 6 - 7 Wyeast Activator packs (depending on the calculated viability of those packs, based upon their packaging date), or by a combination of a starter and direct pitching. Actual pitching rates have probably varied between 1.45 and 1.9 million cells per mL Plato, due to the impreciseness of viability and starter growth calculations.
My oxygenation procedure uses a standard disposable oxygen tank (the red kind from the hardware store) and a regulator attached to a 2 micron stone. Prior to pitching, I open up the regulator all the way and oxygenate for 1 - 2 minutes. Tests with my dissolved oxygen meter have indicated that this provides about 14 - 17 ppm of oxygen.
So, according to what I have read of the brewing literature, these pitching and oxygenation rates SHOULD be ideal. And they work wonderfully for my normal gravity lagers.
I pitch at 46 - 48 F and allow the temperature to rise to 48 or 50 F during fermentation.
Exposure of the beer to oxygen after ethanol has been produced can also produce high acetaldehyde levels, as ethanol can be re-oxidized to acetaldehyde and acetic acid. However, this cannot be the issue because I am using a sealed stainless conical fermenter and actually draining the wort (instead of siphoning) directly into a CO2 purged keg. The keg is purged by filling with sanitizer and blowing it all out with CO2.
Another possibility would be that I am separating the beer from the yeast too soon, or crash cooling before fermentation has finished, or something of that nature. However, I typically raise fermentation temps to 55 - 58 F once the ferment has reached 2 points of final gravity (as measured by a hydrometer, not by the bubbling of an airlock or guestimation) and hold that temp for a week before cooling.
Long warm conditioning is also supposed to reduce acetaldehyde. So I tried letting these beers sit at about 65 F for 3 weeks after the end of fermentation. Though the acetaldehyde character was somewhat reduced by this conditioning, it was still very present. I even tried initiating a secondary fermentation by adding corn sugar to the keg and allowing it to completely ferment out. I've also tried krausening. My hope was that the re-activated yeast would then convert the acetaldehyde. Again, no luck.
Could this character be something else other than acetaldehyde? If so, what compound would make sense? And why would this character reliably show up in every high-gravity lager I have brewed, but in none of the other 25 batches? Apart from this acetaldehyde character, the beers have no other off-flavors, as would be expected in the case of contamination. It is an unmistakably appley, acetic character that is very apparent in the aroma and first few sips, but then becomes less noticeable (but still apparent) as you continue drinking the beer. My wife had the same impression; she assumed I was trying to brew an apple beer.
