Grape skin contact

In winemaking, skin contact, also known as maceration, refers to the process of allowing grape juice to get in contact with grape skins for a length of time. This may be done on a whole bunch, although it is most usually done after the grapes have been crushed, occasionally after pressing to extract juice, and always before fermentation. This skin contact will help to increase organoleptic qualities in the wine, such as aromas, colour and mouthfeel.

How can enzymes help for skin contact? 

Before the fermentation of white wines, skin contact is used to release aroma precursors, which are the components responsible for the wine’s aroma. Aromatic white wine varietals such as Riesling and Gewürztraminer are often made with a brief period of skin contact, which may increase the aroma and complexity of the wine. This may also be done with Sauvignon blanc, Chardonnay, Colombard and Chenin blanc, etc.

Enzymes such as pectinases may be used during skin contact to release aroma precursors by breaking down the cell wall structure of the grapes. Pectinases can help increase the extraction of compounds such as glycosidically bound aroma precursors, which are responsible for the wine’s aroma.

Maceration enzymes aid in this process in numerous ways, including:

  • Pectinases can break down the cell wall of grapes, allowing more aroma precursors to be extracted.
  • Enzymes can stabilise extracted aroma precursors, which can improve wine aroma stability.
  • Reduced maceration time: Enzymes added during skin contact can minimise the maceration time required to extract the desired aroma precursors, reducing the environmental impact of winemaking.
  • Enzymes allow winemakers to fine-tune the final wine’s aroma and taste.
  • Decrease the energy costs by shortening time process.

What makes Rapidase enzyme helpful for skin contact? 

The odourless aroma precursors of volatile thiols occur in grapes, especially in grape skin cells. Producers can get the most out of the aromatic potential of must by using a specific skin maceration enzyme like Rapidase Expression Aroma to extract these precursors and boost the aromatic potential of must.

Rapidase Expression Aroma is a granular enzyme with high pectolytic activity associated with specific maceration activities targeted to aroma precursor extraction. The enzyme, produced by dsm-firmenich in the Seclin facility (France), is active at low doses (1–3 g per 100 kg of grapes), in a short time span, and at temperatures from 8 °C. Normally, Rapidase Expression Aroma needs only 2–3 hours to complete extraction.

Because measurements are required to determine the effectiveness of oenological techniques, we, Oenobrands, frequently conduct large-scale tests to see what happens when enzymes are used. Here are the results when used during skin maceration.

Impact of Rapidase Expression Aroma on aroma precursors release

In recent years, this enzyme preparation has been tested several times, mainly in relation to the extraction of terpenes- and norisoprenoids- glycosylated precursors, with ensuing positive results in support of its use.

Sauvignon blanc and Colombard grapes from the Gaillac AOC (France) were harvested at peak ripeness and divided into uniform batches for the experiment. This included pre-fermentation skin maceration for 6 hours at 18 °C with three different methods (each repeated four times): enzyme-free (control with 1 g/hl of Rapidase Clear added only after pressing), Rapidase Expression Aroma at 2 g/100 kg, and a non-specific maceration enzyme at the same dose rate. The musts were then cold-settled for 72 hours at 0 °C and fermented under identical conditions (temperature, yeast strain, nitrogen nutrition).

Analysing wines for total varietal thiol content highlighted the positive effect of using a specific enzyme, such as Rapidase Expression Aroma. In contrast, very little was achieved by extracting these compounds with a non-specific enzyme (maceration enzyme X).

The table shows the impact of maceration enzyme addition on varietal thiol content in the wines, based on an average of 4 repetitions and variance analysis: materiality at the 5% threshold, according to Newman & Keuls’s means comparison.

Total thiols content (nmol/l)
control8.4
Rapidase Expression Aroma10.4 (+ 24% vs. control)
Maceration enzyme x+ 22% vs. non-specific enzyme)

Impact of Rapidase Expression Aroma on thiols level in wine

Another study focused on the content of thiols in the finished wine

Two equal batches of 600 Kg of Trentino Sauvignon Blanc grapes were used. To get similar batches, the masses of equivalent weight were divided randomly, bunch by bunch. One mass was macerated with Rapidase Expression Aroma at 3 g per 100 kg of destemmed and crushed grapes, whereas the other was not. Maceration continued for 16 hours at 12 °C under argon, then the two batches were pressed separately to give around 70% (p/p). 

After clarification, each triplicate, with and without enzyme, was divided into two equal parts. The first one was added with 30 g/hL of Natuferm Bright, whereas the other wasn’t added with any activator (“no activator”). Alcoholic fermentation was then performed using Fermivin TS28 at 18 °C. 

After fermentation, the wines were sampled for varietal thiol analysis. The results for 3MH are shown here. 

The advantage obtained in terms of volatile thiol in wine appears clearly in samples that have undergone maceration using Rapidase Expression Aroma. The percentage increase in the 3MH content was 24% for the enzyme-enriched sample in the absence of an activator and 17% in the presence of an activator. Also, there is clear evidence that adding enzymes and activators has a synergistic effect that makes it possible to get 51% more 3-MH than in the control sample. 

Concentration of 3-mercaptohexalanol (3MH) at the end of fermentation. Mean values of three replicates for each sample.

These results are complementary to the results obtained in previous years on glycoconjugate extraction and extend the application of Rapidase Expression Aroma to thiolic wines with proven results. We therefore recommend its use on grapes rich in aromatic precursors to maximise the quality potential of the grapes and ensure greater complexity and varietal expression in the wines. In addition, this study showed the great advantage of an integrated approach, combining enzyme, yeast, and yeast nutrition to better valorise the thiol potential of grapes. A collateral benefit of using Rapidase Expression Aroma is that, due to the high concentration of pectinases active on the main and side chains of the pectin, this maceration enzyme will also help you in the cleaning of the musts, allowing the winemaker to decrease or even eliminate the use of the clarification enzyme for flotation or settling.

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