Wine Aromas & Flavors---What Causes Them?

 

      As grape sugar is converted by yeasts into alcohol, thousands of chemical by-products are produced

This is the final article in September’s series on the grape harvest.  Today’s blog discusses aromas & flavors of wine that are a direct result of the fermentation process.   How can a wine smell like a banana?  Why do Sauv Blancs often have a grassy profile?   What is it about Champagne that causes many to have almond nuances?   Did you know that all of these aromas and flavors occur because of chemical reactions during fermentation?  Let me explain.  

               Banana flavors & smells are due to isoamyl acetate produced during fermentation

First, let’s talk about the banana smell and taste.  This is a direct result of the fermentation process where yeasts change grape sugar into alcohol.  The banana profile is the result of a chemical compound by the name of isoamyl acetate, a by-product of yeasts during fermentation.   (Isoamyl acetate is used as an artificial banana flavoring in desserts).    These banana aromas & flavors can be found often in Chardonnay and Pinot Gris, especially from warm climates where grapes are super ripe.  Again, this is a result of the chemical changes during fermentation.

                                Aldehydes form during fermentation & are also present in grass

Have you ever wondered why your Sauv Blanc is reminiscent of freshly mowed grass?   The classical grassiness nose and taste is due to chemicals called aldehydes.  These compounds, released during fermentation, evoke the smell of just-cut grass.   Sauv Blanc grapes have the ability to produce high levels of aldehydes.  Similarly, grass contains elevated levels of this highly fragrant chemical and cutting the grass releases it into the air.

                                One of fermentation's many by-products is benzaldehyde

The almond profile in the real-deal French Champagne is also produced by yeasts as they change grape sugar to alcohol during fermentation.  During the process of making Champagne the fermenting grape juice is often stirred.  The chemical benzaldeyde  is released during the fermentation process and it is dramatically heightened during the stirring (“battonage”).   Benzaldehyde tastes and smells like almonds.

 

In summary, during fermentation yeasts eat the sugar of the grapes and convert it into alcohol.  In this process of fermentation, thousands of various chemicals are produced by the yeasts activities and they often influence the aromas and tastes of wine.

Whole-Bunch Fermentation---What & Why?

                                     Whole grape clusters are used, including all of the stems

This is the second in a trio of articles for the month of September exploring common terms used in the grape harvest.  Those of you who have visited wineries may have heard the term whole bunch fermentation, but do you really know what it means and more importantly, do you understand why it is used?  By the time you finish reading this article you will know what it is, as well as why some winemakers choose to use it.

Whole-bunch (or whole-cluster) fermentation involves the practice of not destemming the grapes.  In fact, the entire bunch (stems and all) goes directly into the fermentation vat.   Prior to World War II, this was generally the way wine was made, as destemming machines weren’t commonly used.   So why would a winemaker use the whole-bunch technique of fermentation rather than destemming the fruit before fermentation? 

            The de-stemming machine (separates the grapes from the stems) is NOT used in                                                                         whole-bunch fermentation

Below are some reasons winemakers may choose to utilize whole-bunch fermentation:

1.   Lower alcohol wines

Warmer weather is increasing the amount of alcohol in wines (riper grapes translate to higher alcohol levels during fermentation.)   High alcohol wines not only decrease the amount of wine that can be enjoyed safely, but are harder to pair with food.                                                                                                                                                                                                             

2.  Paler color wines

               For inky opaque wines such as Syrah or Mourvedre, lightening them up a bit                     could be desirable.  

          3.  Lower acid wines

     Acids play an important part in a wine’s structure, however, too much acidity is       a problem. 

The last blog in this three-part harvest series will discuss the flavors and aromas of wine that are a direct result of fermentation.  Look for it September 27.  

 

Do you Know These Important Harvest Terms?

It's harvest time in the northern hemisphere.   Serious wine lovers who have visited wineries during this period (and/or attended wine appreciation classes) have probably heard most of the below terms of the wine-making process.   But, do you know what they really mean?    Below is a 5-6 minute quiz for 10 terms you need to know.     (Answers at end)  

1.  Alcoholic fermentation:

a.  The addition of alcohol to fermenting grapes.

b.  Alcohol that is produced when grapes are mixed with Sulphur.

c.  The conversion of sugar to alcohol.

d.  Fermentation of grapes which causes higher acidity.

 

2.   Battonage:

        a.  Separating the solid parts of fermentation from the liquid.

        b.  Stirring wine during fermentation.

        c.  The process of transferring young wine from tanks to barrels

        d.  Removing grape skins & seeds from the juice.

 

3.   Brettanomyces:

        a.  Famous French scientist who pioneered cork closures.

        b.  Amount of acidity in grapes.

        c.  Instrument that measures a wine’s tannin level.

        d.  Yeast that causes wine to spoil.

 

4.  Fining:

a.  Sugar level of grapes used to determine ripeness.

b.  Process used to make a wine more clear.

c.  Removing microbes from wine.

d.  Pressing grapes with minimal pressure.

 

5.  Malo-lactic Fermentation

a.  Removal of microbes that interfere with fermentation.

b.  Developed in Spain, this process reduces free radical acids in wine.

c.  A process to remove harmful acids that cause a wine to spoil.

d.  Conversion of harsher malic acid to the softer lactic acid.

 

6.  Must:

a.  Unfermented grape juice

b.  End stage of fermentation

c.  Must-add components to begin fermentation

d.  First inspection of grapes prior to fermentation

 

7.  Lees:

a.  Naturally occurring microbes on grape skins

b.  Yeasts that can interfere with fermentation.

c.  Sediment that occurs during fermentation

d.  Calculation of acidity during fermentation

 

8.  Racking:

a. Evaluating when a wine should be placed in a barrel after fermentation

b.  Process of separating wine from sediment by moving it to another barrel.

c.  Stacking barrels in a winery to facilitate gravity flow.

d.  Process used during bottling to keep wine away from oxygen exposure.

 

9.   TCA:

a.  Destructive chemical that causes a wine to be “corked”

b.  Harsh acid that is found in the skins & seeds of grapes

c.  An array of acid compounds that are vital to the start of fermentation

d.  Test to determine the physiological ripeness of grapes

 

        10.   Topping-off:

          a.  Filling your glass at a wine tasting without permission

          b.  Adding Sulphur to a wine to prevent spoilage

          c.  Filling a wine barrel to its top level to prevent oxidation

          d.  Adding extra grapes during fermentation to enhance flavors 

           

   Answers:

1. c
2. b
3. d
4. b
5. d
6. a
7. c
8. b
9. a
10. c  

How high did you score?  

                9-10 Correct:    Wine-Know!

                7-8 Correct:   WINE OH!

                6-7 Correct:   Whine O

                < 6 correct:   Wine NO!