why don't we worry about hop skunking in glass carboys?

[mojotele]

The compounds in question that cause skunking are primarily riboflavin (from the yeast) and isohumulone (from the hops). Here's a good source.

Riboflavin, a yeast chemical, absorbs light energy with wavelengths of 350 to 500 nanometers (nm). This energy makes the iso-alpha acids release free radicals that combine with sulfur chemicals produced by the yeast, resulting the stinky thiol (sic)

 

[Hermit]

You are telling me my used hops didn't smell like skunk because there was no yeast? I know what I smelled. Sorry.

 

[Shooter]

I bet they smelled skunky, like cousin skunky. Maybe that's different than light struck skunky.

 

[Hermit]

The compounds in question that cause skunking are primarily riboflavin (from the yeast) and isohumulone (from the hops). Here's a good source.

Here is one that says the compounds are created in the boil, which is my experience.


https://www.homebrewtalk.com/wiki/index.php/Can_light_skunk_hops%3F


Dave Wills of Freshops answered this question on the June 1, 2006 episode of Basic Brewing Radio. He confirmed that skunking is the result of light interacting with isomerized alpha acids, which do not exist in the raw hop products (including hop pellets and hop plugs), but are created in the boil.

Nothing about yeast here. Again, my personal experience, listed in my first post, leads me to believe the latter.

What you site appears to be someone that has studied beer after bottling and is talking about one possible path to skunking based on that. Let's face it, probably not too many actual studies are done on wort that is allowed to sit around in the sun since this just isn't done in commercial breweries. Sulfur and other compounds involved can be in the wort without the need for yeast to release it.

 

[mojotele]

Isohumulone is an isomerized alpha acid. So your source just agrees with mine. I made no mention of how the isohumulone was produced. Indeed, it is produced when humulone from hops becomes isomerized during the boil.

Skunk flavor in beer comes from riboflavin absorbing light and causing a chemical reaction in isomerized alpha acids, particularly isohumulone. Here's another source, and another, and another.

This isn't really a matter of belief or opinion. It is fact. Your used hops likely smelled skunky because leftover sugars on the hops were being fermented by wild yeast. Hence, riboflavin was present as well as isohumulone. Add light and you get MBT.

 

[Hermit]

Uh, the hops just rotted. You'd get equally terrible smells if you boil other vegetable matter and leave it sitting around.

You are telling me I can leave just any vegetable matter laying about and it will eventually smell like skunk?

 

[Hermit]

Oh I love how wrong you are Hermit.

For a beer to get skunky, it requires all the ingredients in beer. Yes, the actual chemical comes from the hops, but it requires metabolic activity from the yeast's consumption of malt sugars. I don't know the science - just passing on something I heard from the BN.

Saying that skunkiness comes from light-struck hops is like simplying fermentation to "Sugar + Oxygen = Alcohol + CO2" Technically true but an extreme oversimplification. Sounds like Hermit's the kind of guy who needs that, though.

Before calling me wrong please at least attempt to quote a source and not just say one exists. Again, I'm going from personal experience so your source is going to have to be pretty damned good to make me change what I have experienced first hand.

 

[Hermit]

Isohumulone is an isomerized alpha acid. So your source just agrees with mine. I made no mention of how the isohumulone was produced. Indeed, it is produced when humulone from hops becomes isomerized during the boil.

Skunk flavor in beer comes from riboflavin absorbing light and causing a chemical reaction in isomerized alpha acids, particularly isohumulone. Here's another source, and another, and another.

This isn't really a matter of belief or opinion. It is fact. Your used hops likely smelled skunky because leftover sugars on the hops were being fermented by wild yeast. Hence, riboflavin was present as well as isohumulone. Add light and you get MBT.

You are assuming only one path is available to release the compounds formed in the hops based on what was probably experiments involving bottled beer on a commercial level. This isn't a hard experiment to do though in my area I'd have to wait till next spring to get enough light. Just take my hydro sample outside and let it sit.

Also, your very first source says: "MBT can be prevented by avoiding exposing wort or beer to the relevant wavelengths of light after the completion of the boil."

And: "MBT is the abbreviation for 3-methyl-2-butene-1-thiol, a compound formed by the reaction of isomerized alpha acids, specifically isohumulone, with riboflavin in the presence of certain wavelengths of light."

Are you saying no yeast, no riboflavin?

Second source says the same thing. Again, the isohumulone and riboflavin.

Third source, same story: isohunulone and riboflavin.

 

[Hermit]

I wish I could be as much of a tool as you.

Sounds like you just passed me. Congratulations. :rockin:

 

[Hermit]

http://www.franklinbrew.org/brewinfo/lightstruck.html

Conclusions

Photochemistry undoubtedly deteriorates the quality of beer and protection against light is absolutely necessary. Isohumulones, the main beer bitter compounds derived from hops, undergo light-induced decomposition either on direct illumination with UV-A light, or via a photoredox reaction involving excitation of a visible-light absorber such as riboflavin.

Please notice riboflavin is NOT necessary: undergo light-induced decomposition either on direct illumination with UV-A light, or

I can't find a breakdown for malted barley but since we find riboflavin in malted barley flour, can we assume that it is in the original? Note also "such as riboflavin"in the research. (Actually riboflavin is usually in the germ so much is lost in the milling process so the link figure is probably much lower in riboflavin than the malted barley we use.)

http://nutritiondata.self.com/facts/cereal-grains-and-pasta/5788/2

We now have both bases covered. Neither require yeast. I think someone reading the research decided yeast played a key role since they produce riboflavin and someone else "ass-u-me"d that yeast were therefore needed. Then one web page quotes another until you have all sorts of circular references backing each other up.

I think it is safe to add this to another busted brewing myth at this point.

 

[mojotele]

I think it is safe to add this to another busted brewing myth at this point.

While you make good points, I'm not ready to jump to that conclusion. We haven't really done exhaustive research on the subject. I can't quickly find information on riboflavin concentrations in wort versus beer. All I can find is that the milling of cereals results in a loss of riboflavin, and that concentrations are low in grains to begin with. Thus, a lot of flour is enriched with riboflavin artificially. It also mentions that yeast extract is very high in riboflavin (here's the source).

Most of my quick research turns up academic papers where you can only get the summary now. So, I think I have to conclude this debate as a stalemate. It has moved beyond my abilities as an armchair chemist. I'm just going to end it by saying that riboflavin concentration could definitely play a part, but I'm simply not educated in chemistry enough to say for sure. The guys on the Brew Science forum could probably engage in further conversation on this matter.

 

[Hermit]

While you make good points, I'm not ready to jump to that conclusion. We haven't really done exhaustive research on the subject. I can't quickly find information on riboflavin concentrations in wort versus beer. All I can find is that the milling of cereals results in a loss of riboflavin, and that concentrations are low in grains to begin with. Thus, a lot of flour is enriched with riboflavin artificially. It also mentions that yeast extract is very high in riboflavin (here's the source).

Most of my quick research turns up academic papers where you can only get the summary now. So, I think I have to conclude this debate as a stalemate. It has moved beyond my abilities as an armchair chemist. I'm just going to end it by saying that riboflavin concentration could definitely play a part, but I'm simply not educated in chemistry enough to say for sure. The guys on the Brew Science forum could probably engage in further conversation on this matter.

http://en.wikipedia.org/wiki/Barley

0.1 mg per 100 grams per this source for raw barley. I don't know how much is needed to have the reaction happen to the thresh hold of detection, but this is still ignoring the research I pointed to which indicates that riboflavin is not needed. The compounds are formed during the boil and can be directly broken down by light.

I have a full spectrum florescent fixture over the stove I use to cook my wort. I leave it off when not needed. I'm starting to wonder if people that brew outdoors in full sunlight have taken bits and pieces of information and strung them together to make them feel better about their brewing conditions. Sun doesn't matter until you add yeast....


Quick Edit:
From the quoted article: Riboflavin (RF) or vitamin B2 is present in beer in concentrations around 1 milligram per liter and other flavins have been detected as well. Just using Orfy's mild recipe from the database (because it saves me from doing metric conversion) I come up with enough riboflavin without the yeast. You can check my math of course. But think about this. Is riboflavin a yeast nutrient or a yeast byproduct? Just because yeast can be used as a supplement doesn't mean that yeast are excreting it as waste.
The kinetics of riboflavin production by Saccharomyces cerevisiae and Saccharomyces carlsbergensis in synthetic media and wort were studied. The results indicated that riboflavin was produced by growing cells only. Riboflavin production rate was proportional to growth rate of the yeasts in the exponential phase. Riboflavin was depleted in the stationary phase. The depletion rate was expressed with a first-order kinetic expression in yeast concentration. The kinetics of substrate utilization and ethanol production were also given to describe better the associated phenomena and fermentation pattern.

I'm not going to buy the paper but the abstract indicates that yeast use up their riboflavin at the end of fermentation so I doubt they contribute much, if any, riboflavin to the skunking process.

 

[Rip]

Under-bridge-dweller.
bringer of ill content.

 

[Hermit]

Under-bridge-dweller.
bringer of ill content.
Last edited by Rip; Today at 05:05 PM. Reason: <Decided not to feed the troll>

I'm hungry and the billy goats ran away after I posted the findings backing up my statement.

 

[olllllo]

This thread his Riboflavin and skunk precursor.
Figure out how to be nice or frak off.

 

[Hermit]

Uh, the hops just rotted. You'd get equally terrible smells if you boil other vegetable matter and leave it sitting around.

I wish I could be as much of a tool as you.

Oh I love how wrong you are Hermit.

For a beer to get skunky, it requires all the ingredients in beer. Yes, the actual chemical comes from the hops, but it requires metabolic activity from the yeast's consumption of malt sugars. I don't know the science - just passing on something I heard from the BN.

Saying that skunkiness comes from light-struck hops is like simplying fermentation to "Sugar + Oxygen = Alcohol + CO2" Technically true but an extreme oversimplification. Sounds like Hermit's the kind of guy who needs that, though.

This thread his Riboflavin and skunk precursor.
Figure out how to be nice or frak off.

olllllo Just waiting for these three kind folks to come back and refute the evidence I laid out. I put the effort into backing up what I said, the least they could do is offer something to backup their posts. I'll guess Rip's original statement was about me, but I don't really know that. The thanks I get for doing a little research and sharing it I guess.

Let me recap though.

1. Riboflavin and light is just ONE path to skunking
2. Yeast is probably NOT a source of riboflavin in beer since what they synthesizduring the exponential growth phase is then used up during the stationary phase. (Riboflavin is needed by the yeast and is not a byproduct excreted into the wort along with alcohol and CO2.)
3. There is enough riboflavin in barley to account for the process as described in the linked research.

Conclusion: You do not have to add yeast to the wort before it can 'skunk'.

I'm willing to accept that I am wrong in my interpretation of what I have read but I'm not blindly accepting a bunch of links where people seem to be referencing each other and assuming if it gets said enough times it becomes fact.

 

[SwampassJ]

I'm not here to refute or prove. Someone said something you disagreed with and jumped the ******* gun long before I did.

Geez, and here I was thinking it was HOPS that skunked. So those hops I left too long in the hop bag after boil in the basement and started smelling like skunk must have been exposed to some wild yeast I guess? No, yeast have nothing to do with this.

So before running behind a mod, remember who started the nastiness.

 

[Hermit]

I'm not here to refute or prove. Someone said something you disagreed with and jumped the ******* gun long before I did.



So before running behind a mod, remember who started the nastiness.

You see that as nasty? It wasn't intended to be. I just stated my personal experience and was going off of what I knew. I'd never heard this myth before and was kind of amused by it to be quite honest. I guess my skin must be thicker than most.

 

[SwampassJ]

You see that as nasty? It wasn't intended to be. I just stated my personal experience and was going off of what I knew. I'd never heard this myth before and was kind of amused by it to be quite honest. I guess my skin must be thicker than most.

Same crap. Another miserable hermit to ignore.

 

[Paddle_Head]

The formation of MBT from Iso-Alpha-Acids technically does nit require yeast. However the Sulfur, that is a required element in the chain of reactions, typically is not present in unfermeted wort. Instead sulfur is a byproduct of yeast fermentation. So once wort has been fermented to beer it has the two compounds it needs (Iso-Alph & sulfur) and just needs the appropriate wavelength of light to catalyze the reaction to create MBT.

I've studied this a bit for my job. Never read anything about riboflavin being required but maybe I missed it.

I'm in my phone but would suggest googling (Inuding images) the term Reduced Iso Alpha Acids for a decent overview of the chemistry of MBT.

If I have time later I will link some info from The American Society of Brewing Chemists.

 

[sudsmcgee]

First off, none of the info provided answered all of my questions. Second, unless an actual controlled experiment is done, we're all just guessing.

Third, Hermits attitude does not appear to be that one of a true scientist.

 

[Hermit]

The formation of MBT from Iso-Alpha-Acids technically does nit require yeast. However the Sulfur, that is a required element in the chain of reactions, typically is not present in unfermeted wort. Instead sulfur is a byproduct of yeast fermentation. So once wort has been fermented to beer it has the two compounds it needs (Iso-Alph & sulfur) and just needs the appropriate wavelength of light to catalyze the reaction to create MBT.

I've studied this a bit for my job. Never read anything about riboflavin being required but maybe I missed it.

I'm in my phone but would suggest googling (Inuding images) the term Reduced Iso Alpha Acids for a decent overview of the chemistry of MBT.

If I have time later I will link some info from The American Society of Brewing Chemists.

I'll be interested in seeing what this says but there is sulfur in the wort. Yeast need sulfur. People even regularly add sulfur to the water in the form of gypsum ( Hydrated Calcium Sulfate):

Yeast requires sulfur for the production of proteins, coenzymes, vitamins, etc., and takes up organic sulfur from wort, chiefly as methionine, and inorganic sulfur in he form of sulfate (152). http://hbd.org/brewery/library/mashtun/kleyn.html


Since you are posting from your phone I'll assume you mean 'sulfur in the required form' maybe since the yeast may have cytoplasm but lack cyclotrons? (I guess I'd better make this clear that this is a joke and not a put down ) I'd have to think the methionine is from the barley.

From what I've read there just hasn't been much in the way of studies on wort since it generally isn't subjected to light in a commercial setting so there is little need/incentive to study it for skunking. The focus is on the finished product. The mechanisms in place post fermentation doesn't preclude others pre fermentation. I've skunked hops without yeast and very little, if any, of the proper wave length light.

 

[Hermit]

First off, none of the info provided answered all of my questions. Second, unless an actual controlled experiment is done, we're all just guessing.

Third, Hermits attitude does not appear to be that one of a true scientist.

Well, I don't seem to fit in here. I'm willing to have the mods delete my account as long as they also willing to delete my posts since I won't be around to defend myself. I think that would be the only fair way to do it. Run a poll if you want. Seems most would agree that I'm not welcome here. I obviously am not a 'true scientist' but I seem to be willing to do the leg work to learn.....

 

[sudsmcgee]

Well, I don't seem to fit in here. I'm willing to have the mods delete my account as long as they also willing to delete my posts since I won't be around to defend myself. I think that would be the only fair way to do it. Run a poll if you want. Seems most would agree that I'm not welcome here. I obviously am not a 'true scientist' but I seem to be willing to do the leg work to learn.....

So do it and come back with results. That's all I'm saying. We can theorize all day.

 

[Hermit]

So do it and come back with results. That's all I'm saying. We can theorize all day.

I've already stated a few times I've skunked hops without the benefit of yeast. I've also said that when conditions are better I'll set my hydrometer sample out and check it. It will probably be much harder to detect 'skunk' over the malt aroma of unfermented wort however so I'm not sure if it will be a good test, especially since most of what I do is lightly hopped anyhow. You IPA brewers in sunny climes wanna take this one on?

 

[sudsmcgee]

Cool. I appreciate your willingness to do this.