Brett or Reduction, Can You Tell The Difference?

In the recent David Z diatribe thread, Tom B mentioned that people often think a wine is bretty, when it is actually reduced.

Can you reliably and consistently tell the difference? If so, how?

How quickly can you make your determination?

Does wine age matter?

I think I can but I’ve never run any lab tests to confirm my assumptions. In my experience (or, in my belief), reduction isn’t such a chameleon as Brett, and can resolve itself with time or air or copper. Brett, on the other hand, doesn’t go away, only gets worse.

I should probably admit that I rarely drink Bordeaux and thankfully do not have to taste more than a handful of wines containing Grenâche every year. Reduction can of course mimick excessive oakiness, TCA, mouldiness and many other off-seeming odours. Still, I’ve never seen it confused with brettanomyces.
Nonetheless, I am rather sensitive to brettanomyces and have a good handle on it and in off-chance I should forget; I have a handy box with bottles containing wine faults standing by.

In case of doubt, Frank already outlined how some aeration will easily determine which is what anyway.

Where did you get your fault kit? I’m interested in getting one for my own personal amusement.

Years ago when I took my wine courses we had something like this:

The two qualities are Sooooooooo different, how could you not?

brett, on nose.
reduction, less so on nose, more on palate

I agree that people confuse reduction and brett all the time.

I used to a lot more so. I may still confuse some types of brett/reduction but Ive got pretty good at identifying the type of brett that is similar to those used in beer. Drinking Belgium beers has been a revelation in identifying that organism.

In my opinion, one tell tale sign is that if the stink blows off faster than a wine’s fruit awakens during aeration then its likely reduction and not brett.


The one Henry just linked to is the best commercial box I know of. In my case, I happen to know a few chemistry professors who are always eager to prepare vials of certain compounds for me, as long as I keep pointing them towards good deals on their favourite wines. [wink.gif]

I may be mistaken, but until very recently there was very little actual knowledge on these issues out there. It took me until about five years ago, before I finally got a good grasp on reduction and what it does in a wine. I’ve had many an argument over reduced wines since, with people telling me all sorts of things and have yet not to be vindicated. This leads me to suspect that to many, it is still a question mark these days.
I fail to understand the confusion over brett however, but then again I’ve never seen it as a huge problem unless it overpowers the wine. In my days as a sommelier, I sold many a bretty Châteauneuf-du-Pape and only very rarely did I encounter one that was excessively so. The guest who drank them sure didn’t seem to mind.
I realize that these days, whole wheels with different aroma’s associated with brettanomyces are floating around the web, but I see little scientific research behind them. In short: can someone explain the problem to me?

Reduction = rubber hose, onion, cabbage and/or garlic. One way to tell reduction is to put a small copper pipe fittling in the wine. If the smell goes away, its reduction. FYI - pennies don’t really work that well.

Brett - there are 10 or so different strains, but the two most commom are 4EG and 4EP. 4EP is more band aid, and 4EG is smoke and damp basement.

Here is a tech sheet from ETS on Brett.

Just to clarify, 4-EP and 4-EG are not strains of Brettanomyces but byproducts of Brett’s metabolism.

I have to disagree with you pretty vehemently on this. I don’t always know how to describe the sensory effects of either brett or reduction on the palate, but they are (for me) much easier to discern and describe (and most importantly, distinguish) through their aromas. The main compounds associated with brett have really no relationship to those which underlie aromas of “reduction” (mercaptans, i.e., compounds that incorporate sulfur in a particular way, vs. phenolic derivatives, which contain no sulfur).

Some of the descriptions above are pretty good for “reduction” compounds: tires, rubber hose, skunk, garlic, etc. But those smell nothing like the main brett compounds.

To add and divert a little to this discussion, another close relationship that I find interesting is the closeness in molecular structure between the compounds responsible for Brett, and those most responsible for the aroma of smoke. Wish I could figure out how to place images side by side, which would make this easier, but hopefully this will make a little sense. Ignore the differences in orientation, that doesn’t matter.

Two of the main chemical compounds produced by Brett yeast:

4-Ethylphenol (4-EP)

4-Ethylguaiacol (4-EG) Same as above, with the addition of the methoxy group (-OCH3)

Two of the main compounds that account for the strong aromas in smoke:

Guaiacol (note the similarity to 4-EG above, but without the ethyl group

4-Methylguaiacol (4-MG) Very similar to the 4-EG above, but with a methyl (-CH3) instead of Ethyl (-CH2-CH3)

And just for grins, here’s the structure of TCA (2,4,6-Trichloroansiole), another phenol-based compound, but in this case with 3 chlorines, responsible for the aroma of “corked” wine:

My own theory is that the “smoky” or “bacon” character often attributed to some wines (e.g. northern Rhone syrahs) is actually due to very low levels of Brett contamination, and not to any innate character of the syrah grape.

Alan - fascinating. I once read somewhere that the bacon character in N. Rhône Syrah is attributable to the grapes, but when found in N. California Syrah it’s due to barrel treatment. The article didn’t provide any further analysis to back up that claim, and I took it with a grain of salt.

OT - can someone explain the wine fault that presents as sweet corn? That kind of flavor is a marker for me in many of a certain board darling’s wines.

Reduction is tricky because it’s a range of flavors that vary widely, whereas Brett is much more constant. I don’t think of them as similar.

Sounds like it could be DMS - dimethyl sulfide

I can confirm this. Interestingly, certain types of blood vessel malformations in the brain are treated with a glue called Onyx that is dissolved in DMSO (dimethyl sulfoxide). The DMSO is broken down in the body to DMS and excreted through the lungs and skin and the smell is overwhelmingly like canned corn to many people. My coworkers are always surprised to know that that smell can be a fault in wine.

Ok so which one was affecting a wine i had last night? On the nose - and lasting the entire 2+ hours it was in my glass - it was incredibly stinky in an earthy/ merde kind of way. On the palate it cleaned up a bit and suggested a beautiful wine was underneath. But the nose remained very offputting to me all night. The wine alongside had a bit of similar stink that blew off. Neither smelled of garlic or smoke.

The problem is that brett and reduction aren’t that simple. You can’t say that brett equals one thing and reduction equals another.

First of all, reduction just means something is not oxidized. But for argument’s sake, let’s say that when we’re talking about wine we’re only talking about sulfur when we talk about reduction.

There are many different types of sulfur compounds and depending on their concentration, the same compounds can even seem to smell different. So there is a range of aromatics that might be caused by reduction. In general, sulfur compounds stink, but they don’t all stink the same way. I think there are somewhere around a hundred different sulfur compounds that have been found in wine - not entirely certain about that though and don’t feel like looking it up at the moment. In any event, there are many of them and depending on what combination they occur in and their concentrations, they manifest themselves differently. Some react with oxygen when given air and form larger compounds that aren’t as volatile - that’s what “blowing off” usually is. The sulfur is still there, but as part of a heavier molecule that is less volatile and therefore harder for us to detect.

Without adequate oxygen, nitrogen, and nutrition, yeast can instead use available sulfur and can make hydrogen sulfide, among other things. In addition, some strains of yeast are more prone to form sulfides than are others, and sulfides generally stink. Racking, topping up, filtering, and bottling allow the incorporation of oxygen and thus help to prevent sulfide formation. The addition of elemental sulfur, either in the vineyard or to the wine on the other hand, can do just the opposite. Those sulfides don’t blow off with aeration and they aren’t easily oxidized, again, they simply form disulfides or heavier, less volatile, sulfur compounds for which we have higher sensory thresholds. Some however, can precipitate with copper, so copper treatment during the winemaking process is used. Pennies don’t have that much copper these days, but if you have an old one, or some copper pipe, that can work.

Some people don’t think that a little stink is a flaw and in fact, sulfur compounds aren’t always unpleasant - the petrol scent of Riesling is the most obvious, but the yeasty or bread-like aromas from aging on lees that you get in whites like chardonnay or sparkling wine is also a reductive scent, and what I think people sometimes call “mineral” notes in highly acidic whites may be yet another.

Finally, some grapes are more prone to reduction than others. Syrah for example, or Mourvedre. It’s one reason for adding Counoise in the south Rhone, because that grape is prone to oxidation. One of the developments in the south of Spain recently has been the production of Monastrell with careful attention to prevent reduction - it produces wines that are completely different from the stinky wines of yesteryear.

Brett is just as confusing.

it’s all over everything. There’s absolutely no reason to think it’s particularly associated with Chateauneuf du Pape - that’s a huge misunderstanding. It’s associated with all wines around the world, particularly the “peasant” wines. Until recently, CdP was one of those regions. The great influence of Parker on CdP has been cleaning up the winemaking. Same in the North Rhone and in Bordeaux. Same in most of Spain and Italy and certainly in central and eastern Europe.

In the US, UC Davis preached clean winemaking, so brett wasn’t such an issue but that doesn’t mean it can’t be.

With a little oxygen and some nutrients, brett of some strain or another can grow using the alcohol in the wine as a source of carbon, some amino acids in the wine for nitrogen, and even some of the sugars in the wood of the barrels, particularly the toasted woods.

So the wine needs to be able to eat up, or use any available oxygen, so as to deprive the Brett of any ability to grow. Also, Brett grows quickly at temperatures above 60 degrees F, so if you have any in your wine, keeping the wine cold is important. So to the OP’s question about wine age - it can matter quite a bit if brett has been allowed to flourish.

High acidity can inhibit some brett growth. But “modern” wines, with higher pH, higher sugar levels, and in some cases, reduced use of sulfur, all contribute to the growth of brett. So even if the winery is clean, the winemaking style may contribute to brettiness in the wine.

And again, because there are so many strains of brett, and because it manifests itself differently depending on what it is associated with and how concentrated it is, it’s pretty much impossible to say that the absence of a particular aroma is definitive proof of the presence or absence of brett. It can contribute to the band-aid, leathery, smoky, earthy aromas that some wines have, or even some of the buttery notes, or it can be awful.

Because both sulfur compounds and brett can stink, they both can produce what people call a “barnyard” character, but again, that’s imprecise and there is barnyard and there is barnyard.