Why no late additions of sugars to bump alcohol?

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winnph

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I've wondered for awhile why most fermentation techniques discourage late infusions of sugar/wort. In other words, why can't I take a finished beer or mead, decide I want to bump up the alcohol a bit, and just add a half-gallon of high gravity wort? Is it because there's a risk of oxygenation, even though the yeast should be using up some of that oxygen to consume the new sugar? Or is it one of those traditional things that doesn't have any basis in actual results? Or something else?
 
If the beer is finished, it won't ferment properly and will be sweet. Many beers are made with sugar, honey, syrup additions near the end of fermentation, but you can't do that to a "finished" beer. Mainly due to the high alcohol content and the lack of active yeast. Its not a very hospital environment for them when they are swimming in their own waste.. (alcohol)
 
I mean if there's still a yeast cake, seems like a little rousing would do the trick on that front. If the issue is high alcohol, then the issue should be the particular strain's tolerance, and I'm not talking about going beyond the yeast's tolerance.

I guess I've just never seen these beers that are made with late additions. The only times I've seen people ask about adding more wort or sugar near the end of fermentation, the responses are all discouraging it.

So, if my question was starting with a faulty premise, then I apologize and withdraw it.
 
Lots of brewers add some sort of sugar after initial fermentation. Many lambics have fruit added to the secondary. Other brewers might add table sugar later on to get a dryer final product, or non fermentable sugars to get a sweeter product. As long as you aren't going past the yeasts tolerance or overly agitating the beer when you add the extra sugar, then you should be fine.

I think a lot of the replies you've seen might be when someone is trying to salvage a beer that they think might not turn out good. Most of the replies for those types of questions say not to add anything because the beer will probably turn out fine. Kind of a RDWHAHB type of reply.

If you brew a beer with the intent of adding more fermentables later on, then I don't think there is a problem with that.
 
winnph said:
I've seen people ask about adding more wort or sugar near the end of fermentation, the responses are all discouraging it.
.
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You may be using the wrong search terms. I find negative responses are sometimes from people who just repeat what they have read. If you want to try boosting..I say go for it ...you will learn more about yeast then someone who say's ..."you can't do that"..
 
FYI, really high alcohol beers sometimes involve adding fermentable sugars a little at a time throughout primary fermentation.... Some even involve adding a second more tolerant yeast after the first one goes dormant.
 
Thanks for the responses... I don't really have a desire to boost alcohol at this point, but I was pondering doing a brew where I slowly step up from a 2 gallon batch to a 6 gallon batch, with higher and higher gravity additions at each step.

I've definitely heard of adding more tolerant yeasts when your initial one craps out, but I've just never seen anyone employ a process like the one I'm considering.
 
winnph said:
Thanks for the responses... I don't really have a desire to boost alcohol at this point, but I was pondering doing a brew where I slowly step up from a 2 gallon batch to a 6 gallon batch, with higher and higher gravity additions at each step.

I've definitely heard of adding more tolerant yeasts when your initial one craps out, but I've just never seen anyone employ a process like the one I'm considering.
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I wouldn't boost the volume of the beer that drastically. I would imagine your flavor profile would be quite skewed if you do that, in part because your yeast won't propagate sufficiently to handle the later increase in gravity and volume (unless you keep adding yeast as well, which would get expensive). A more standard practice is to brew 4+ gallons, and then feed the yeast daily with a very concentrated sugar solution (just enough water to dissolve the sugar or DME) until you have achieved your objective. Your proposal is worth a try though, maybe in a side-by-side experiment with the more traditional method.
 
ArcaneXor said:
I wouldn't boost the volume of the beer that drastically. I would imagine your flavor profile would be quite skewed if you do that, in part because your yeast won't propagate sufficiently to handle the later increase in gravity and volume (unless you keep adding yeast as well, which would get expensive). A more standard practice is to brew 4+ gallons, and then feed the yeast daily with a very concentrated sugar solution (just enough water to dissolve the sugar or DME) until you have achieved your objective. Your proposal is worth a try though, maybe in a side-by-side experiment with the more traditional method.
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I guess my question is how is a large increase in volume here any different from bumping up bottle dregs from 50ml to 1.5L for pitching into a 5-gal batch? Why won't the yeast reproduce and increase, just like when you add wort to a starter?

Or, viewed another way, wouldn't the yeast cake under a 2-gallon batch be plenty of yeast for pitching into a later 4-gallon batch? What's the difference between pitching that yeast cake into a later batch and adding enough wort that the current 2-gallon batch "becomes" a lower-gravity 4-gallon batch? The only difference I see is the alcohol in the beer, so is the answer that the presence of alcohol inhibits yeast reproduction?
 
By the way, my reason for asking this question is basically because it seems to me that if this sort of process can work, it would allow people with relatively small brewing setups to brew fairly large batches, so long as they have a large fermenter. For example, if your brew setup can't handle more than 5 gallons, but you want to brew 20-gallon batches and can easily acquire a large enough fermenter, then add 3-5 gallons of wort every week or two until it's full.

The other option is the more traditional approach of fermenting separately and blending after they're all finished. But I just don't see why that approach is preferred, and it requires multiple fermenters being taken up with this single batch.
 
I don't think there is any consensus for sugar/wort additions being "bad", actually. At least I've never heard/read that from any reputable source.

Someone already pointed out the example of a truly big beer, where the osmotic shock of pitching directly into the full-strength wort would likely mean the yeast wouldn't ferment to anywhere near terminal gravity.

There are also many commercial brewers who are brewing on their original brewhouse but knocking out multiple batches into new, much larger fermenters. A half-dozen brew sessions per fermenter isn't uncommon (e.g. filling a 100 bbl conical using a 15 bbl system). In that case, fermentation is well under way by the time the last batch of wort hits the fermenter. There's actually a big advantage to that technique in that it dramatically reduces the amount of yeast that needs to be pitched initially.
 
winnph said:
I guess my question is how is a large increase in volume here any different from bumping up bottle dregs from 50ml to 1.5L for pitching into a 5-gal batch? Why won't the yeast reproduce and increase, just like when you add wort to a starter?

Or, viewed another way, wouldn't the yeast cake under a 2-gallon batch be plenty of yeast for pitching into a later 4-gallon batch? What's the difference between pitching that yeast cake into a later batch and adding enough wort that the current 2-gallon batch "becomes" a lower-gravity 4-gallon batch? The only difference I see is the alcohol in the beer, so is the answer that the presence of alcohol inhibits yeast reproduction?
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Oxygen is the difference. Yeast need it reproduce effectively.
 
ArcaneXor said:
Oxygen is the difference. Yeast need it reproduce effectively.
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So what about oxygenating the sweet wort before adding it to the fermenter? Would this actually risk the cardboardy oxygenation effects, or would it just be used by the yeast when it's eating the new sugar?

Which brings me back to a brew science question -- what is it that triggers the off flavors associated with oxygenated beer, and would those be prevented or mitigated by the addition of new sugars for the yeast to consume along with the oxygen? In other words, we all know that fermented beer + oxygen = cardboard, and we all know that sweet wort + oxygen + yeast = good beer, so what happens if you have fermented beer + sweet wort + oxygen + yeast?
 
Please do not oxygenate your beer. Oxygenate your wort prior to fermentation as much as you can.

If you look at the link I posted earlier, the trick to adding corn sugar to increase the alcohol content (boosting) is to build a healthy colony of yeast at the onset and to slowly feed more sugar to the yeast during active fermentation step wise. This way a larger colony is not needed as there is not a significant jump in the gravity. The colony just needs to be healthy as the period of active anaerobic fermentation is extended.
 
beerkrump said:
Please do not oxygenate your beer. Oxygenate your wort prior to fermentation as much as you can.

If you look at the link I posted earlier, the trick to adding corn sugar to increase the alcohol content (boosting) is to build a healthy colony of yeast at the onset and to slowly feed more sugar to the yeast during active fermentation step wise. This way a larger colony is not needed as there is not a significant jump in the gravity. The colony just needs to be healthy as the period of active anaerobic fermentation is extended.
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But that misses the point of my question -- if you have 2 gallons of mostly-fermented beer and 2 gallons of unfermented wort, and you aerate the unfermented wort before combining it with the fermented beer, will the oxygen immediately do horrible things to your beer (and if so, please explain the chemistry behind that), or will it be consumed by the yeast as the new sugars in the wort are consumed?
 
beerkrump said:
Please do not oxygenate your beer. Oxygenate your wort prior to fermentation as much as you can.

If you look at the link I posted earlier, the trick to adding corn sugar to increase the alcohol content (boosting) is to build a health colony of yeast at the onset and to slowly feed more sugar to the yeast during active fermentation step wise. This way a larger colony is not needed as there is not a significant jump in the gravity. The colony just needs to be healthy as the period of active anaerobic fermentation is extended
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Odd, Sam calagione recommends aeration the beer in his dema-goddess ale recipe just prior to pitching distillers yeast, used in conjunction with table and Demerara sugar to raise abv to 14-16%.

I think oxygenation is only a problem after the beer is fermented. During fermentation, the creation of co2, and the yeast growth cycle should be enough to drive off/absorb oxygen before it causes a problem.

I second the small sugar additions. He recommends an ounce of sugar a day for 3 weeks, starting when initial fermentation is nearly complete, pitching the distillers yeast around day 13.
 
winnph said:
please explain the chemistry behind that
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You'll probably have to hit the literature for that, although it may even be difficult to find there since this is a pretty unorthodox procedure. Maybe e-mail one of the brewing schools and see if they can answer your question.
 
Oxygenating mid-fermentation may not be SOP in most breweries, but I think it's a pretty well-established method of improving yeast performance. As long as the oxygen levels are modest (<15 ppm) and active fermentation will continue for at least a few hours, I don't think there would be an issue with oxidation. If there were, the same problems would occur when oxygenating pre-fermentation.

At any rate, regardless of its validity as a "standard" technique, my opinion is that it's the way to go when brewing a big (>30°P) beer.
 
I think there's a fine (but potentially considerable) line between what the OP is suggesting and some of the other quoted methods for boosting. Boosting is done while fermentation is still active, so the yeast are happy to continue dividing using the new sugars as food.

What winnph is suggesting is going a couple weeks between additions of new wort. In that time the yeast is sure to flocculate and begin to go dormant. At the very least its life cycle is no longer in the rapid dividing stage. At this point it would be possible to rouse the yeast and get them to start dividing again with well oxygenated wort, but there is a lag time associated with this. Here comes the fine line: is the lag time shorter than the amount of time it takes for the oxygen to start oxidizing the beer and ruining the flavor, or will the yeast start to use the oxygen before bad oxidation occurs?

Considering that the lag time will be at least 12-24 hours and we all know what a beer that was left out overnight tastes like, my guess is that this would result in ruined beer.

If you want to do an experiment, though, please do!
 
dinertime said:
I think there's a fine (but potentially considerable) line between what the OP is suggesting and some of the other quoted methods for boosting. Boosting is done while fermentation is still active, so the yeast are happy to continue dividing using the new sugars as food.

What winnph is suggesting is going a couple weeks between additions of new wort. In that time the yeast is sure to flocculate and begin to go dormant. At the very least its life cycle is no longer in the rapid dividing stage. At this point it would be possible to rouse the yeast and get them to start dividing again with well oxygenated wort, but there is a lag time associated with this. Here comes the fine line: is the lag time shorter than the amount of time it takes for the oxygen to start oxidizing the beer and ruining the flavor, or will the yeast start to use the oxygen before bad oxidation occurs?

Considering that the lag time will be at least 12-24 hours and we all know what a beer that was left out overnight tastes like, my guess is that this would result in ruined beer.

If you want to do an experiment, though, please do!
Click to expand...

So your response has me thinking maybe the best method would be to add wort that is not oxygenated (though just adding it will necessarily introduce a little oxygen), rouse the yeast a few times, and then oxygenate once the yeast looks to be gearing up in response to the new sugars.

Though, I'm still curious about the chemistry of beer oxidation... is this a process that might reverse somewhat in the presence of vigorous fermentation? In other words, is it possible that active fermentation might "clean up" some of the oxidized tastes?
 
I think someone else made this point, but maybe it got overlooked. I've heard of yeast "getting tired" if they've been fermenting in a high gravity wort (like a barley wine). Harvesting that yeast and pitching it into a new batch doesn't work well for some brewers. You might have to think about repitching when you add in the second batch of wort.
 
I would imagine that the yeast would not actively get rid of the majority of oxidized flavor compounds. The problem is that the oxidations are somewhat random--they can occur on any compound at a variety of locations within the molecule. The yeast don't have the specific enzymes or pathways to clean up all of these possible oxidation products.

This stands in contrast to diacetyl, for example, because it is a single, specific compound that is a natural byproduct of the yeasts' growth, and they have a recycling/salvage pathway specifically for it. That's not the case for nearly all other oxidated species.
 
dinertime said:
I would imagine that the yeast would not actively get rid of the majority of oxidized flavor compounds. The problem is that the oxidations are somewhat random--they can occur on any compound at a variety of locations within the molecule. The yeast don't have the specific enzymes or pathways to clean up all of these possible oxidation products.

This stands in contrast to diacetyl, for example, because it is a single, specific compound that is a natural byproduct of the yeasts' growth, and they have a recycling/salvage pathway specifically for it. That's not the case for nearly all other oxidated species.
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So what prevents the wort from becoming severely oxidized when you oxygenate it prior to fermentation? Is it only compounds resulting from fermentation that become oxidized, not compounds that also exist in unfermented wort?
 
winnph said:
So what prevents the wort from becoming severely oxidized when you oxygenate it prior to fermentation? Is it only compounds resulting from fermentation that become oxidized, not compounds that also exist in unfermented wort?
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That would be my guess, yes. Not to say that some compounds in the wort aren't oxidizing, but they must not be the ones that create the 'oxidized beer' flavor.
 
dinertime said:
That would be my guess, yes. Not to say that some compounds in the wort aren't oxidizing, but they must not be the ones that create the 'oxidized beer' flavor.
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I wonder if anyone has ever done experiments to see what specific compounds produce the oxidized beer flavor. There must be someone out there reading this forum who has access to the type of lab equipment to answer this question definitively...
 
winnph said:
So what prevents the wort from becoming severely oxidized when you oxygenate it prior to fermentation? Is it only compounds resulting from fermentation that become oxidized, not compounds that also exist in unfermented wort?
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The big one is trans-2-nonenal (paper/cardboard), which is formed by oxidation of lipids that are present in the malt. My belief is that aerating/oxygenating before or during fermentation is simply a numbers game: the oxygen is being taken up by the yeast before substantial oxidation of wort compounds occurs. If one were to oxygenate a batch of wort and then wait a few days before pitching yeast, I wouldn't be at all surprised if the resulting beer tasted oxidized.
 
a10t2 said:
The big one is trans-2-nonenal (paper/cardboard), which is formed by oxidation of lipids that are present in the malt. My belief is that aerating/oxygenating before or during fermentation is simply a numbers game: the oxygen is being taken up by the yeast before substantial oxidation of wort compounds occurs. If one were to oxygenate a batch of wort and then wait a few days before pitching yeast, I wouldn't be at all surprised if the resulting beer tasted oxidized.
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By that reasoning, you should be able to add more wort, aerate, and then the newly reactivated yeast will use up the O2 before those lipids become oxidized on a large scale. Nice post.
 
DregAddict said:
By that reasoning, you should be able to add more wort, aerate, and then the newly reactivated yeast will use up the O2 before those lipids become oxidized on a large scale. Nice post.
Click to expand...

Yes, and if you are adding a secondary yeast strain you pretty much need to do this. I'm about to do it on the Utopias clone when pitching the WLP099, I did it with the DFH 120 before that when I added EC-1118, and before that I even used O2 on a stuck Saison (at 1.014) that I pitched champagne yeast into. The yeast will take up the oxygen within about 30 minutes, far too fast for any oxidative flavors to develop.

It's best to add additional sugars while the yeast are still actively fermenting, but as has been proven with fruit in the secondary, you can get yeast to consume sugars after they have settled out. They'll gladly come back to the dinner table for a second round any time you offer it to em! :D
 

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