Acidity sensation in a wine

Training on detecting the Acid Flavour at the Tasting Panel of Vila Viniteca

How do we evaluate and quantify the acid elemental taste in a wine? Before and during the training of the Tasting Panel, we had many doubts about how to correctly evaluate the sensation of acidity in a wine. What role does sweetness play in the perception of acidity in a wine? And astringency? What about alcohol?

Our Tasting Panel evaluates the acidity of a wine according to its intensity through a linear scale. In order to train them, reference patterns were created for each of the intensity zones of the scale, from 0 (null perception) to 10 (clearly identified and intense perception). The challenge and the objective were to obtain the most faithful and representative patterns to the reality of the sector. For its development we are guided by different hypotheses based on our knowledge and experience with trial and error tests.

Where does the acidity of a wine come from?

According to the RAE Dictionary of the Spanish Language, acidity is something that causes a sour or vinegar-like taste, and in chemical language a solution with a pH * lower than 7 is called acid.

Acidity is one of the essential components in wine and has several functions: at a biological level it restricts the action of bacteria that could damage wine, since in many cases they are unable to survive in an acidic environment; and at the organoleptic level it provides a sensation of balance and freshness.

It is also a factor to take into account for the longevity of a wine in the bottle, normally, the higher the total acidity, the better the storage in the bottle.

Where does the acidity of a wine come from? All acids come from the pulp of grape berries. The must that is obtained after its pressing is mainly made up of water, sugars, different types of organic acids, phenolic and nitrogenous compounds, aromas and minerals.The three major acids that we find in must are, firstly, tartaric acid, secondly malic acid and, lastly, citric acid. The levels of natural acids present in the berries will depend on the degree of ripeness of the grape, the variety of the grape and cultural practices. As the degree of ripening increases (increase in sugars present in the fruit), its acid content decreases. Therefore, broadly speaking, we can say that in hot areas the acids decrease more quickly than in cold areas. For example, in the Mosel region (Germany) or Bourgogne, due to its climate, higher natural acidities can be obtained compared to warmer areas such as the south of the Rhône or the Priorat.

Each type of acid causes a different organoleptic sensation, tartaric acid is considered the hardest and the most structured, malic acid as metallic, lactic acid as creamy, and citric acid as fresh. The total acidity of a wine is the sum of all its acids and is normally expressed as tartaric acid.

Our Panel evaluates the intensity of the sensorial perception of the set of acids or total acidity of a wine on the palate.Due to the differences in the composition of red wines and white wines, we evaluate them under different intensity scales. So just like with the sweetness attribute, we created two specific intensity scales: one for whites and one for reds. Once these premises are established, we begin to elaborate the reference patterns.

Next, we explain how we develop the reference patterns for each of the areas of the acidity intensity scale, based on our hypotheses and the conclusions obtained after each test.

Methodology

White and red wines

1st Hypothesis: Real wines with a known total acidity content (g / l)

We start from the assumption that with the exact analysis of grams of total acidity per liter (expressed in tartaric acid) in different wines we can create an ascending scale of acidity. We assume that the higher the total acidity, the greater the sensation of acidity on the palate. For red wines we do not have the exact analytics, and to make an ascending scale we rely on our experience.

First references used for white wines:

Reference Intensity Analytics
Riesling 2015 (Mosel) High 8,4 g/L
Vinho Verde 2016 (Portugal) Average + 6,7 g/L
Xarel·lo 2016 (Catalunya) Average 5,8 g/L
Códega do Larinho, rabigato, donzelinho, cercial among others 2015 (Douro) Average – 4,8 g/L
Gewurztraminer 2015 (Alsace) Low 3,8 g/L

First used patterns for red wines:

Reference Intensity
Barbera 2014 (Piemonte) High
Pinot Noir 2015 (Sancerre) Average +
Pinot Noir 2014 (Bourgogne) Average
Garnatxa, cariñena y tempranillo 2016 (Catalunya) Average –
Touriga franca, touriga nacional, tinta roriz, tinta amarela and others 2015 (Douro) Low

Conclusions

The samples do not have obvious differences between them with respect to acidity. We realize that, especially in white wines, sweetness plays a very important role in the perception of acidity on the palate, reducing it considerably. As for the reds, the astringency and alcoholic sensations confuse the panelists when evaluating the acidity attribute.

An added difficulty is that each sample has different structural characteristics (tannins, astringency, body …) that complicates its evaluation..

Another problem was the lack of reproducibility, since with each vintage the characteristics of the wine vary. For this reason we consider another hypothesis.

Acidity scores given by panelists to 5 red wine samples on a linear intensity scale during a training session in November 2017

2nd Hypothesis: Modification of the total acidity concentration (g / l) of the wine

We decided to use a single base where we add different concentrations of acid to be able to make an ascending scale with different intensities. For white wines we use a Xarel·lo 2016 (Catalunya) with 5.8 g / l of total acidity (expressed in tartaric), and for the red scale patterns a base wine of Garnacha, Cariñena and Tempranillo 2016 (Catalunya ) with 5.1 g / l of total acidity (expressed as tartaric). Our base wine would correspond to the average zone of the intensity scale, in order to reach the low values ​​of the scale we lower the wine with water to obtain acidity equal to 0 (expressed in tartaric). From this solution, we add the following concentrations of tartaric acid:

  • 2 g / l tartaric
  • 4 g / l tartaric
  • 5 g / l tartaric
  • 6 g / l tartaric 
  • 7 g / l tartaric
  • 8 g / l tartaric
  • 10 g / l tartaric

Conclusions

Although the perception of acidity was ascendant, the sensation of the wine base lowered with water was far from that produced by a real wine. We discarded the patterns and re-formulated a new hypothesis.

3rd Hypothesis: Modification of the concentration of total acidity (g / l) in a deacidified wine

We work with a neutral and slightly acidic wine base in which we add different concentrations of acid to cover all the areas of the scale.

We add potassium bicarbonate to two base wines: a white one made with Xarel·lo 2016 (Catalunya) with 5.8 g / l of total acidity (expressed as tartaric), and a red one made with Garnacha, Cariñena and Tempranillo 2016 (Catalunya) with 5,1 g/l total acidity (expressed in tartaric).

Thanks to the action of potassium bicarbonate, finally the two base wines have a total acidity content of 2 g / l (tartaric) in white wine and 2.5 g / l (tartaric) in red wine.

We test the de-acidified base wine and add three different types of acid separately: tartaric, lactic and citric. In the first tasting we discarded the use of citric acid as it is not well integrated. We add different concentrations of tartaric acid and lactic acid separately in order to decide which the best acid to create the ascending scale of intensity. We prepare the following concentrations of total acidity (expressed in tartaric):

  • 2,5 g / l
  • 3,5 g / l
  • 5 g / l
  • 7,5 g / l
  • 9 g / l

Conclusions

With both white and red wine, the addition of tartaric acid and lactic acid is well integrated into the whole. To choose the most representative scale, we decided to present the samples to the panelists. Finally, we conclude that the acid that best integrates is lactic acid, both in white and red wine.

Difficulties

  • One of the difficulties encountered when carrying out the acidity patterns was to achieve an optimal base wine for the creation of an ascending scale of intensity.
  • In the case of red wines, it was difficult to get panellists to isolate the perception of astringency when evaluating acidity.

Conclusions

The total acidity concentration of a wine does not indicate its strength at the organoleptic level.

To facilitate the training of the panellists, and as we have already seen with the patterns of the sweetness scale, it is much more advisable to have a single neutral wine base and modify it as needed. We have been able to observe that it has a better acceptance by the panellists to elaborate the patterns of an attribute with a wine with the same characteristics in terms of astringency, body or flavours, among others, to better learn to evaluate a specific attribute.

Lactic acid is better integrated than tartaric acid.

We developed a tasting protocol to help our panellists better evaluate acidity (Annex 1)

Finally, our patterns for the acidity characteristic are as follows:

Scale zone Final concentration g / l lactic acid in wine (expressed as tartaric)
WHITES 0 – 2 : low scale zone + 2,5 g / l
2 – 5 : average-low scale zone + 3,5 g / l
5 – 7 : average-high scale zone + 7,5 g / l
8 – 10 : high scale zone + 9 g / l
REDS 0 – 2 : low scale zone + 2,5 g / l
2 – 5 : average-low scale zone + 3,5 g / l
5 – 7 : average-high scale zone + 7,5 g / l
8 – 10 : high scale zone + 9 g / l

It must be taken into account that the linear intensity scale of acidity for wines that our Panel has is its own. We have prepared it under our criteria and taking into account more parameters than the total acidity of the wine, such as sweetness or astringency. It has also been designed according to our criteria and perceptions within a group of people belonging to the same society, culture and customs.

* pH: Index that expresses the degree of acidity or alkalinity of a solution.

Annex 1

Evaluate samples tastefully: acidic

  1. Taste the wine by taking a generous sip and initially spreading it over the entire surface of the tongue without moving it.
  2. Perceiving the acid taste on the tongue, the sensation may be more intense on the sides of it.
  3. In a second phase, make the wine run through the entire palate.
  4. Spit out the wine.
  5. Right after spitting out the wine, hold your tongue still for 10 seconds.
  6. Evaluate the salivation caused by the tasted wine. The high acidity of a wine can cause abundant salivation.

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