Aroma Trials

By: Thomas J. Payette, Winemaking Consultant

OK– your wine smells good but can it have a better aroma?  Always keep this in mind as a winemaker or winery owner.  The largest violation of “house palate”, a process where winemakers overlook their wine flaws because they taste their own wines too often, is the oversight that their wines may be reduced.  Reduced or reductive is a broad term that covers many sulfide compounds ranging from hydrogen sulfide, rotten egg, to other more complex aromatics that may smell like cabbage, dill weed, onions or even garlic.

Early detection of these flaws is imperative to clean up the wines and to make sure these compounds do not evolve toward other more difficult to remove compounds, mercaptans, often needing ascorbic acid additions to make the wine reactive to the most commonly used remedy copper sulfate.

Copper sulfate trials are extremely easy and there is no excuse for each wine created not to go through at least three quick trials with copper sulfate to see if the wine aroma will indeed become improved.

When? The author recommends each wine be reviewed:

  1. Anytime one suspects a wine to be reduced or smells hydrogen sulfide in the fermenter.
  2. Review all wines just after the fermentation process as a blanket rule process to discover any wines that may improve from the copper sulfate addition.
  3. Three months prior to bottling and preferably before any stability processing actions have been taken.
  4. Roughly three days before bottling.

Why? As suggested, in the first sentence of this article, winemakers should review each wine’s aroma to see if faults exist.  Some of the faults do not express themselves directly as Hydrogen Sulfide or Mercaptans.  Some wines may have just enough of one of these compounds, or both, to lightly mask the underlying fruit expression.  Winemakers may not know nice smelling wine can actually smell nicer.  It is an easy test – so why not run these trails!

Where? Most winemakers will perform this test in the winery laboratory, away from the chill of the cellar floor, where a wine will have the ability to open up and allow for undisrupted critical analysis of the wine’s aroma.  If winemakers cannot find this tranquility in their winery, it is recommended to take a sample home and do the trials in a home environment.  One must be able to focus and have conditions for the wine to open up.  This is critical.

Tools needed

  • Clean wineglasses with a narrow focused opening to the bowl (I.N.A.O. style). All exact same size and style.
  • Glass watch covers for each glass (optional but highly recommended).
  • Representative samples of each wine to be sampled.
  • 1.0% Copper Sulfate solution (One percent).
  • Spit cup.
  • Clear and “in tune” nasal passages.

How? This test is very easy to perform as long as the environment is proper for the aroma analysis.  If possible, work closely with someone else to mix up the wineglasses after treatment so you will be blind on this analysis.  If this can’t be done – do proceed since experience will help take any bias out of the results.

  1. Place three (“aroma free”) dry clean wine glasses on a table and label them x, 4 and > or any other random characters that may not lead a person to select one wine glass over another but allow them to identify what glass or glasses may be different.
  2. Fill each glass with the same quantity of wine. This is often between 80-100 milliliters per wine glass depending on the wine glass size.
  3. Have another person place 1 drop of the 1% Copper Sulfate into one of the glasses and to swirl all three glasses equally to mix the addition into the wine and to treat each glass equally with a swirl.
  4. Place watch glasses over each of the glass openings and leave the glasses to sit for about 5 to 10 minutes.
  5. Approach the wine glasses and remove the watch glasses one at a time to smell the aromas in the headspace of the glass. Go through the wines at least three times and perhaps more to select the wine that smells the best.  Record your results.
  6. Leave the wine glasses for another 15 minutes or longer and re-approach in the same fashion by smelling each wine individually and select the glass or glasses that smell the best.
  7. After determining that the wine is actually changed and changed for the better, have the person that added the copper sulfate to the glass reveal the glass that was treated.
  8. Mentally extrapolate after collecting all the data whether the addition of copper sulfate had a positive impact on the wine or not. Be aware not to select the copper sulfate addition wine – just because it is different.  The wine should smell better – not just different.
  9. Once an addition is deemed helpful, proceed to making the adjustment in the cellar as referenced below under calculation. This test is not quantitative.

This test is sometimes known as a triangle test.

Spicing it Up!

Once you and your assistant get comfortable with the test, he or she can be instructed to switch around the treatment regime to perhaps treat two of the three wineglasses.  This will keep the person smelling the wines on their toes to actually identify what wine smells better and to truly focus on the improved wine.

Referencing the fact that a spit cup was listed under the “Tools needed” list above, one should have their spit cup ready.  This should be used if by habit one should accidentally taste the wines.  Remember, technically, Copper Sulfate is a poison so winemakers should resist tasting our trails and only focus on the aromas.

One can build on this test to correct Mercaptans, also.  Mercaptans are Hydrogen Sulfide based compounds that have transformed to a more complicated chemical compound.  Ascorbic acid trials may need to be tested for effectiveness in these cases.  Reference other sources to review this process as it will not be covered at this time.


In my opinion there is no truly reliable calculation for this test to determine quantitatively how much copper sulfate to add.  In most cases it is best to add small quantities of copper sulfate to a wine nearing the range of 1.0 gram per 1000 gallons to as low as one-half a gram per 1000 gallons to clean up small defects.  This is a good starting point.  From experience, you may start to recognize a wine that may need more Copper Sulfate to combat more pungent aromas.  This chemical is a strong oxidizer so use limited amounts.  Overuse could have serious downsides to your wine.

Removal of Copper After Use

In most cases, only small amounts of copper sulfate are used to clean up a wine so we rarely need to address lowering the copper content in the wine.  Please recognize when larger quantities have been used.  Use an outside laboratory to actually measure the amount of residual copper in your wine.  In many cases, for white wines treated prior to protein fining with bentonite, they may clean up on their own.  The author has seen copper levels drop significantly after protein fining and filtering of white wines.  Many years ago, wines may have needed a “Blue-Fining” but one rarely has those issues in today’s winemaking plus they are not permitted in the United States.

The Future

According to some scientist we need to more closely look at nutrients and their role with the yeast.  In some cases too much or too little nutrients may cause Hydrogen Sulfide production and it is thought to link into the micronutrients.  Nitrogen issues may not be the driving factor here.  This will help us stay away from using copper sulfate, which does have adverse affects to the wine in addition to cleaning the wine up sensorialy.  Until that time we need to address the problem in a fashion we can, such as copper sulfate.  Stay tuned.

Other Helpful Tips

  • Caution is expressed not to confuse a change in aroma in the wine with this being considered better. This is called “Stripping”.
  • Caution is also expressed not to consume / taste wines that have added copper sulfate added during these trials.
  • Do these trials next to any wine that may be a follow-up bottling for that wine to see if consistency is achieved and to focus on other nuances that may easily be changed.
  • The Tax and Trade Bureau does regulate the amount of copper sulfate a winemaker may use.
  • Please research this amount and have a clear understanding of the use of copper sulfate. It is a strong oxidizer and considered poisonous.
  • A reduced character may become hard to notice if the wine has just been racked, transferred, filtered or in any way brought into a less anaerobic state.

These reductive compounds may be just under the threshold of the human nose sensitivity and difficult to smell.  If this same wine is bottled, the reductive character may become very pronounced.

Screw cap wines may need more serious aroma reviews and evaluation since these seals are more anaerobic than previous seals. Caution is urged when making wine to be bottled under screw cap to make sure no underlying reductiveness is present.  Outside labs also offer “headspace sniffing” if one feels they need additional help.

Wines exposed to light may become “lightstruck”.  Light struck is a term used to describe that light has attacked an amino acid and caused a mercaptan-type aroma.  This phenomenon is somewhat more common with flint bottles and sparkling wines.


Amerine, M.A., Berg, H.W., Cruess,W.V. 1972. The Technology of Wine Making

Dharmadhikari, M.R., Wilker, K.L. 2001. Micro Vinification.

Zoecklein, B.W., Fugelsang, K.C., Gump, B.H., and Nury, F.S. 1999. Wine Analysis and Production

Verbal discussion with Mr. Jacques Boissenot, Mr. Jacques Recht, Mr. Joachim Hollerith and Mr. Chris Johnson.

Short Course:

  • This is qualitative and not quantitative
  • Make sure the change in aroma is not just “stripping”
  • Copper Sulfate is a poison – be careful to check residual copper present after larger uses.
  • Know when to use outside “electronic sniffers”

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