Key aroma compounds in wine vary depending on the type of wine, but there are a few main compounds to consider. Some of these compounds occur naturally in grapes, while others are formed during the winemaking process and ageing.
These compounds can “break” the aromatic buffer, which is constituted mainly by fermentative esters. That means that their unique scents are perceivable. Usually, their odour detection thresholds are quite low, and their average levels in wine are much higher than their detection thresholds.
Here, we would like to present some key compounds of the wine aroma and information on their valorisation using our winemaking biotechnology solutions.
In white and rosé wine, varietal thiols are among the most potent key aroma compounds as they directly impart the wine aroma profile of several varieties like Sauvignon Blanc, Colombard, Verdejo and Grenache but obviously also Chenin Blanc, Manseng, and even Muscat, depending on the winemaking process used (yeast strain, temperature, nutrition, etc.). In red wine the situation is quite different, as thiol levels determined in Cabernet sauvignon, Merlot or Carmenere are much lower. However, an interaction between 3-mercaptohexanol and 4-mercapto-4-methylpentan-2-one was highlighted, which could explain the blackcurrant notes of some red wines. Recent studies at the AWRI also showed the impact of the grape variety on the hedonic perception of those thiols.
Thiols are sulphur compounds found in wine, known for their powerful aromas. Key thiols include 3MH (3-mercaptohexan-1-ol), A3MH (3-mercaptohexyl acetate), and 4MMP (4-mercapto-4-methylpentan-2-one). They are formed during alcoholic fermentation from odourless precursors mainly linked to a cysteine molecule or a glutathione present in grape skins.
3MH produces notes of grapefruit and citrus; A3MH offers aromas of passion fruit and tropical; and 4MMP brings scents of boxwood and guava.
Both yeast strain and nutrition status are key impact factors for varietal thiol release during the alcoholic fermentation.
Two types of yeast strains can be distinguished among the “thiolic yeasts”.
– the so-called releaser yeasts exhibit a high capacity to release thiols from their precursors, 3MH and 4MMP.
– the so-called converter yeasts are strains able to either release thiols from their precursors and convert the 3MH released into its acetate (3MHA). This conversion can be very interesting in terms of aroma profile since it shifts the profile from citrus to passion fruit and tropical fruit notes, but in addition, it increases the aroma intensity due to the 15 times lower olfactory threshold of 3MHA vs. 3MH. Thus, increasing the 3MHA/3MH ratio is an opportunity to have young wines with very intense and pleasant flavours.
In addition, yeasts that are able to produce high levels of esters and thiols can also be a good option since a good balance between thiols and esters has been shown to be responsible for the tropical fruit profile in rosé wines from Provence, a profile highly preferred by consumers.
We can name the “thiolic yeasts” that Oenobrands supplies: Alchemy II, Legacy Vin 7, Legacy Vin 13, Legacy NT 116, Fermivin TS28, Fermivin 4F9, and, to a lesser extent, Fermivin IT61.
In this context, several scientific and technical studies have pointed out not only the importance of the YAN level but also its composition. Indeed, ammonium salts, usually added to correct nitrogen deficiencies, are detrimental for thiol release since they inhibit the thiol precursor uptake by the yeast. This mechanism, called nitrogen catabolic repression, can explain the positive effect of the addition of nutrients rich in amino acids (yeast derivatives).
To further enhance the production of varietal thiols, you may consider the use of Natuferm Bright. This innovative product has been proven to boost aroma production during fermentation, resulting in wines with intensified aroma profiles.
Its application at yeast inoculation will enhance the release and/or conversion properties of the yeast, and a fractionated addition at yeast inoculation and after a third of alcoholic fermentation will enhance thiol release and esters production, magnifying the complexity profile of the said wine.
Understanding these nuances in yeast selection, nutrition, nitrogen composition, and the potential benefits of products like Natuferm Bright is where we can help you maximise varietal thiol expression in your wines and create a truly remarkable sensory experience.
Esters are synthesised during fermentation, both alcoholic and malolactic. Three main families of those fermentative esters are present in wine, resulting from different biosynthetic pathways in the yeast. Ethyl esters are formed through the enzyme-catalysed reaction between ethanol and short-medium-chain fatty acids coming from the lipid metabolism, while the formation of acetates of higher alcohols is linked to the amino acid metabolism, or between fusel alcohol and acetic acid. Finally, the esterification of branched fatty acids by ethanol results in branched ethyl esters. In such a case, yeast cannot create them at concentrations far from chemical equilibrium; therefore, chemical esterification alone raises their concentration after alcoholic fermentation.
The presence and concentration of those esters can vary based on grape variety, but mainly according to yeast and bacteria strains, fermentation temperature, and winemaking techniques.
In wine, esters contribute to fruity and floral aroma and constitute what was qualified as the aroma buffer by Prof. V. Ferreira from the University of Zaragoza (Spain).
The balance between the different families changes over time, resulting in a change in the aroma profile. Linear ethyl esters are much more stable acetates, and branched ethyl esters concentrations are even increasing during wine storage.
The linear esters often contribute to fruity and floral aromas in wine. Here are some of the main linear esters found in wine:
– Ethyl acetate (Ethyl ethanoate): This linear ester imparts fruity notes reminiscent of apples, pears, and citrus fruits to wine.
– Ethyl butyrate (Ethyl butanoate): Known for its sweet, fruity aroma with hints of pineapple, this ester can enhance the overall complexity of a wine’s bouquet.
– Ethyl caprotate (Ethyl hexanoate): Ethyl hexanoate adds a delicate fruity character, often described as a combination of apples and pineapples, to the wine’s aroma.
Acetates contribute to a wide range of aromas, including fruity, floral, and exotic. Here are some of the main acetates in wine:
– Isoamyl acetate (3-methylbutyl ethanoate): This ester is responsible for banana-like aromas and adds a tropical fruit complexity to wine. This is the only one that is often at sufficient concentrations to break the wine aroma buffer and be perceivable.
– Isobutyl acetate (Isobutyl ethanoate): Known for its sweet, fruity scent reminiscent of pears and bananas, isobutyl acetate can enhance the overall fruitiness of wine.
– Hexyl acetate: This ester contributes to the fruity character of wine, with notes of banana and pineapple.
– 2-phenylethyl acetate: These rose notes can diversify the aroma profile when produced in high quantity (by Fermivin VINEAE, for instance).
Even if those esters constitute the wine aroma buffer and thus are not supposed to be perceivable per se, changes in their levels and/or proportions can modulate the fruitiness of the wine and also its shelf life.
Then, by understanding the contribution of these esters and managing their levels, you can craft wines with distinct aroma profiles, a critical aspect of wine quality. Managing yeast selection, fermentation conditions, and nutrient levels is all part of optimising ester synthesis in wine.
We offer tools and expertise to help you optimise ester production, allowing you to fine-tune and control the sensory attributes of your wines.
The essential factors are:
The yeasts like Fermivin AR2, Legacy WE372, and Fermivin E73 will promote more of the acetates, explaining their use for early-release wines with strong fruitiness.
Others, like Alchemy I, Fermivin 4F9, Alchemy III, Alchemy IV, and Fermivin P21, will promote more stable esters, explaining their immediate positioning for wines to be aged with medium- to premium wines.
Some, such as Legacy VIN13, produce a well-balanced level of esters from all families.
Refer to the yeast selection section to understand our portfolio.
Glycoconjugates in wine are a diverse group of compounds. In this section, we will describe only the glycoconjugates containing terpenes (i.e., geraniol, linalool, nerol, terpineol, citronellol, etc.) and norisoprenoids (β-damascenone, β-α-ionone, etc.). Glycoconjugates are very stable compounds, and it is mainly during wine ageing that we can observe their hydrolysis because of the slow speed of this reaction. When the aroma part of those glycoconjugates is released, it can impart floral, fruity, and spicy notes to the wine.
These precursors are found at high levels in Muscat, Gewürztraminer, Albariño, and Riesling cultivars and at lower levels in other grapes. But even at these low levels, the volatile aroma compounds formed can contribute to the complexity of the ageing profile. One of those compounds, β-damascenone (a C13-norisoprenoid), has been shown to be a very potent fruity aroma enhancer in red wines.
In some cases, glycosides may contain compounds that, when released, contribute undesirable aromas to the wine. For example, in certain instances, glycosides can contain precursors to smoky or reductive aromas.
The presence of glycoconjugates in grapes can be influenced by grape variety, pedoclimatic conditions, cultural techniques (nitrogen fertilisation, canopy management), and ripeness at harvest.
During the winemaking process, glycoconjugates can break down due to enzymatic and chemical reactions and this release of the bound aroma compounds significantly contributes to the wine’s final aroma and flavour profile.
As said, the terpenic and norisoprenoidic varietal aromas, mainly responsible for floral and fruity notes, are present in grape, must, and wine in two forms: free and thus odor-active, or glycosylated, i.e., linked to a glucose or to a diglycoside moiety, non-volatile and thus odour-neutral.
The transformation of the glycosylated forms into the free form significantly increases the aromatic expression of the wine. It happens naturally during fermentation and storage, but only to a small degree and slowly. Using certain enzyme preparations can bring out varietal character that might not be expressed otherwise.
Rapidase Revelation Aroma is an enzymatic formulation manufactured by dsm-firmenich from a selected strain of Aspergillus sp. It has the advantage of a complete set of glycosidase activities for highly targeted and effective action. The active mechanism of this enzyme acts on glycosylated terpenols and norisoprenoids, significantly increasing the intensity and complexity of aroma for Muscat, Traminer, or Riesling, but also for other “non-terpenic”cultivars such as Sauvignon blanc, Chardonnay, Verdejo, Pinot Gris, and Viognier.
As an example, we present the result of a study carried out a few years ago in Switzerland at the Changins Institute. Rapidase Revelation Aroma (2 g/hL) was tested to see how it affected the release of terpenes in Pinot noir, Chardonnay, and Pinot gris, which are not aromatic grapes. After each time interval, the wine was treated with 5 g/hL of bentonite in order to block the enzymatic activity. The effect of the enzyme is evident in all three wines; the highest content of free terpenes was reached after eight weeks for Pinot noir and after six weeks for Chardonnay and Pinot gris.
Rapidase Revelation Aroma can also be used in red varieties without negatively impacting the colour of the wine. Several trials on Syrah, Pinot noir, Tempranillo, Cabernet, Grenache, Malbec or even on some country specific varieties such as Carmenère in Chile, Touriga Nacional in Portugal or Aleatico in Italy. We obtained excellent results in releasing terpenes and norisoprenoïds that enhanced the aroma complexity of the wines. Norisoprenoids such as β-damascenone will also contribute to some floral characters, global fruitiness, and aroma longevity.
Besides ethanol, which is the most abundant alcohol, yeast is also able to produce other alcohols, mainly methanol and higher alcohols. Their levels depend on the yeast strains and the fermentation conditions (such as turbidity and temperature). Most of them are detrimental to the wine aroma profile since they increase the heavy fusel notes. In brandy production, the management of their level is crucial since they dramatically decrease the quality of the distillates.
Only a few of them are considered positive. It typically includes ethanol (ethyl alcohol), which serves as the primary alcohol in wine and contributes to its overall mouthfeel. Other alcohols, such as isoamyl alcohol, can impart fruity and floral notes, while phenylethyl alcohol may add a hint of rose-like or floral aromas when present at very high concentrations. Some yeast strains, such as Fermivin VINEAE, are able to acetylate 2-phenylethanol into its acetate, which presents a lower odour threshold and highly imparts the wine aroma profile.
Dimethylsulfide has been considered a defective aroma for years. It is still the case in dry white wine, but recent studies about sweet and red wines have demonstrated their positive role, either as a fruity aroma enhancer at subdetection concentrations, or as a direct contributor to an ageing aroma with odours reminiscent of olives, forest undergrowth, and truffles.
Even if a biogenetic pathway exists during fermentation (from sulphur-containing amino acids, peptides, and dimethyl sulfoxide), DMS is normally stripped by fermentation gases. The DMS responsible for the ageing bouquet is formed during wine storage from a precursor.
This precursor is present in grapes and is called potential in DMS (PDMS) since its analytical quantification was done by the release of DMS after a heat treatment in alkaline conditions. It has been identified as S-methylmethione, but the word PDMS remains.
This precursor is strongly degraded by yeast during fermentation, and only the residual PDMS can contribute to DMS formation. The degradation ability of the yeast is a genetic trait, and studies are ongoing in order to improve yeast strains and lessen potential wine spoilage.
Nitrogen nutrition has also been shown to have an impact on PDMS preservation. The use of nitrogen nutrients such as Natuferm Fruity during fermentation can be a tool to manage residual PDMS after AF.
Biotechnological approaches can be used to manage pyrazine levels in wine. For instance, some yeast strains have been selected to help reduce pyrazine concentrations during fermentation.
With a highly qualified team of experts in many fields, Oenobrands strives to offer winemakers’ novel and scientifically sound solutions, as well as to highlight the positive synergies between its products.
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