Secondary Aromas in Wine: An Overview

Secondary aromas in wine arise from the chemical changes effected on the wine by the process of fermentation.

Although in casual wine tasting we often use the terms ‘aroma’ and ‘bouquet’ interchangeably, convention calls for a distinction. We usually use the term ‘aroma’ for primary smells that are generally typical of the grape varieties the vintner has used to make the wine.

On the other hand, we tend to reserve the term ‘bouquet’, for the more complex smells that result from the winemaking process. These bouquet smells include both the secondary aromas from fermentation and tertiary aromas from aging.

Secondary Aromas in Wine: Brewer’s Yeast

Secondary aromas in wine emerge from the fermentation process. Fermentation in wine is catalysed by a species of yeast known as Saccharomyces cerevisiae, which is also known as brewer’s and baker’s yeast. This yeast converts the natural sugar in grapes into alcohol as well many other different compounds. We perceive these compounds as the wine’s Secondary Aromas. It is precisely the complex, multifaceted nature of these compounds that suits the term ‘bouquet’ more comfortably than the more one-dimensional term ‘aroma’.

Unsurprisingly, many secondary wine bouquets have ‘yeasty’ and “fungal’ overtones. Bouquets usually associated with fermentation that you may detect include:

• Sourdough Bread
• Yoghurt
• Creme Fraiche
• Beer
• Parmesan
• Mushroom
• Soy Sauce
• Yeast

Secondary Aromas in Wine: Brettanomyces

However, wine fermentation is more interesting and complex than simply the conversion of grape sugars into alcohol via the addition of brewer’s yeast.

Wild yeasts known, as Brettanomyces or Brett, are not intentionally added but occur naturally in wineries, even under modern hygienic conditions. Their presence is considered a wine flaw by most but some wine enthusiasts appreciate the base-notes that Brett yeasts provide.

At its best, Brett provides a complex bouquet of:

• Cloves
• Spice
• Bacon
• Wild Game

At its worst, Brett evokes:

• Spoilt Cheese
• Band-aid
• Barnyard
• Sweaty Socks

Secondary Aromas in Wine: Malolactic Fermentation

Another creator of secondary aromas in wine is malolactic fermentation or MLF.
Malolactic fermentation is not actually due to yeasts but due to bacteria such as Oenoccocus Oeni, Pediococcus and Lactobacillus. These bacteria convert the tart malic acid into the much softer lactic acid.

MLF rounds off and smooths out wine flavours, so most red wines go through it. However, only a fifth of white wines will be allowed to undergo MLF because acidity is often desirable in whites.

MLF creates a bouquet of secondary aromas evocative of:

• Butter
• Cream
• Hazelnut
• Chocolate

However, if not handled properly MLF might result in odours such as:

• Fetid Milk
• Sauerkraut
• Sweat
• Rancid Butter

Summary of Secondary Aromas in Wine

Secondary aromas in wine refer to the bouquet of smells fermentation creates. During the fermentation process, primary aromas associated with the grape varieties used are further developed and transformed. This occurs through the addition of brewer’s yeast, or Saccharomyces cerevisiae, as well as through the occurence of wild yeasts known as Brettanomyces or Brett. Lastly, selected bacteria are used for malolactic fermentation, which softens the wine flavours by converting malic acid into lactic acid.

Armed with this quick overview of take-away facts about secondary aromas in wine, you should now be able to associate primary aromas you detect in wine to the different types of fermentation during the wine making process.