Climatology plays a fundamental role in the last stages of vine development. In particular, high humidity and temperature above 25 ºC as the season progresses, increase the risk of fungal infections, especially powdery mildew, downy mildew and botrytis (but also infections by Aspergillius, or Penicillinum), which, in turn, weaken the plant and become an entry vector for other fungi. These infections can cause significant losses in production if they are not properly controlled and treated, both due to the reduction of the harvest, the affectation of the vine or the loss of quality of the must produced. In addition, the infection produces a reduction in the available nitrogen (which may compromise the fermentation process), a loss of total acidity and an increase in volatile acidity that subsequently complicates the entire winemaking process.

Powdery mildew (Uncinula necator) attacks any green part of the vine. In the leaves it is recognized because an ash colored powder appears on both sides; on shoots and branches shoot fuzzy dark green to black spots; and the clusters are covered with a powder that stops the growth of the skin of the grain, producing oxidative changes and putrefactions in the pulp.

The temperature between 25 and 28 ºC, humidity and lighting are the factors that condition the development of this fungus that, carried by the wind, spread the disease to any green part of the plant.

Downy mildew (Plasmopara viticola) is one of the most well-known and serious diseases. It attacks all the green parts of the grape in the phenological period of awakening, the vegetative period, in spring. Then it remains dormant in the autumn in the form of an oospore in the plant remains until the next cycle. Once germinated and spread by the wind, they penetrate the tissues of the plant through the stomata, giving rise to an intercellular mycelium and to what is known as primary contamination. Then the secondary infestation will begin and the symptoms will manifest on the vine in the form of yellowish spots on the leaves, limited by the nerves, and a white and cottony formation of spores on the underside, from which it will reach the cluster, which will turn grey -moved first and dehydrated later.

Esca is associated with infection by fungi Stereum hirsutum Per. and Phellinus igniarius Fr. that penetrate the wood through significant wounds produced by pruning. The symptoms usually begin in full bloom or already in the middle of summer and consist of the appearance of internervial discolorations, and on the edges of the leaves, yellowish in the white and reddish varieties in the inks that come together and dry up in the center. The leaves end up falling, one or more arms of the strain can die (even all of it). Berries are not fattening properly and may not reach maturity; and in the most extreme cases, especially with high temperatures, the death of the vine occurs.

The anthracnose of the vine is a wood disease caused by the fungus Glocosporium ampelophagum that attacks all the green organs of the vine, producing lesions characterized by the presence of a whitish central area surrounded by a black halo. but it is mainly in the herbaceous shoots where attacks mainly occur. The leaves dry and fall off, leaving irregularly shaped holes surrounded by a purplish black border. The branches appear burned, are short, winding, crooked and have numerous secondary and tertiary ramifications that give the strain a scrubby appearance. In the inflorescences when the attack is very intense, they dry completely and the loss of the harvest is total. On the fruit, if it has survived, black spots appear that fade through its center, turning grayish-white and peeling off the affected skin.

Botrytis (Botrytis cinerea) is caused by a fungus that can attack all the green organs of the strain, but the greater severity is due to the attack on the clusters during veraison, when the accumulation of water, sugars, and polyphenols begins in the grape. The infection produces a dense cottony film that covers the grain, which begins a process of putrefaction, oxidation and acidification, to end up withered and parched. However, when the fungus infects the ripe berry, once veraison has been overcome and at the maximum level of sugars and polyphenols, the drying effect of the fungus (noble rot) produces a concentration of sugars and acids that results in an extremely appreciated must for its organoleptic characteristics.

In all cases, the infection causes a significant change in the metabolism of the berry, altering its chemical and organoleptic characteristics. A recent study (1) found that powdery mildew infection resulted in decreased vanilla-like aromas due to a variety of very subtle changes, including decreased levels of vanillin, octanoic acid, and ethyl isobutanate ester , 2-methylbutanoate acetate, and 3-methylbutyl acetate, all of them compounds that contribute positively to the aroma of the wine, resulting in ‘flat’ wines, with little appeal. In contrast, botrytis infection produced an increase in lactones (fruit odors), isobutanol, isoamyl alcohol, furaneol, and homofuraneol (roasted and vanilla), among others, which resulted in an increase in positive aromas.

Although in many cases it is possible to detect infected bunches with the naked eye, visual detection requires the implementation of specific selection procedures, either manual or automated, which cannot be applied to large quantities of grapes in a quick time, nor is it effective. When the infection exists, it does not manifest itself visibly in the form of damage to the berry. The alternative is detection using adequate analytical methods that indicate the presence of specific markers. Some of these infection markers look for compounds generated by the metabolism of the fungus. Among them, glycerol, gluconic acid and lacassa stand out. Of all of them, gluconic acid is the most used due to its easy implementation in the laboratory and its high correlation with the level of infection and its use is preferable to that of the measurement of lacassa (non-existent in the case of Botrytis infection) or glycerol (due to the variability associated with very low levels). The enzymatic gluconic measurement method is an officially adopted method by the OIV (2) for both must and wine.

Gluconic acid is a metabolic product of the oxidative aerobic fermentation of glucose produced by numerous species of fungi, and has been widely studied in the case of Botrytis infection. The glucose oxidase from the fungus oxidizes the C1 aldehyde from glucose to carboxyl, producing glucolactone which, in turn, is spontaneously hydrolyzed to gluconic. By itself it is not toxic nor does it contribute unpleasant aromas to the wine, but its presence is indicative of the metabolism of the fungus. In this sense, the determination of gluconic has been routinely implemented in many Protected Designations of Origin as a quality parameter both in the reception of the grape and in the acquisition of must or wine and is one of the elements considered in the evaluation of the same. The enzymatic method validated by the OIV as the official type II method (resolution OIV-OENO 622-2019) is based on the transformation of gluconic into ribulose with production of NADPH and the reaction is monitored by means of the variation of absorbance at 340 nm. This reaction is very fast and allows accurate results of the gluconic concentration to be obtained in approximately 2-3 minutes, and the process can be automated on chemical analyzers.

Sinatech has dedicated reagents for the determination of gluconic acid for the Y15 / Y25 and Dionysos systems (and easily adaptable to other automatic or manual systems) according to the official OIV method, with a measurement range of 0.06 to 2.00 g / L and analysis time of 3 minutes.

Test / Kit
Measure range
2×40 mL + 1×12 mL
0.06 – 2,00 g/L
2×30 mL + 1×15 mL
0.06 – 2,00 g/L


(1) Lopez-Pinar et al. Effects of Bunch Rot (Botrytis cinerea) and Powdery Mildew (Erysiphe necator) Fungal Diseases on Wine Aroma. Front. Chem., 28 March 2017:

(2) Resolución OIV-OENO 622-2019:

For more than 10 years, Sinatech’s commitment to the winemaker has been working side by side to provide the most appropriate analytical solutions to the control and monitoring of the winemaking process. Automated methods easily adaptable to any work routine, with a personalized advisory team to help you quickly and smoothly implement.

Sinatech: TeamWork.



Enzymatic vs FTNIR

The most widespread analysis systems in oenology are certainly the enzymatic and the NIR (or better, FTNIR). There are many supporters of one or the other system, which certainly have pros and cons, but to compare them it is necessary to know how they work evaluating their characteristics and limitations.

Principle of operation of enzymatic analyzers

Enzymatic analyzers base their operation on the Lambert-Beer Law (the absorbance (A) measured at a given wavelength (λ) is linearly proportional to the concentration (C) of the substance and on the length of the optical path (a ) through a constant of specific proportionality for each substance called molar extinction coefficient (ελ): A = C in ελ). If we had a pure solution of a substance with known ελ, it would be sufficient to measure the absorbance of the solution to determine the concentration of the substance. However, all the samples that are analyzed, both in the oenological field and in other areas, are very complex solutions and the absorbance is the sum of all the contributions of the substances present in the sample.

However, there are substances that react specifically with individual molecules, and only with them (as happens, for example, in an enzymatic reaction, where the enzyme is a specific catalyst for a given reaction). Even through one or more cascaded chemical reactions, new molecules can emerge that are distinguished from the rest of the sample by their high absorption at specific wavelengths. Therefore, it will be possible through these reactions to obtain a solution in which to measure the absorbance (or the variation of absorbance against time) that will be proportional exclusively to the analyte sought.

Enzymatic systems, such as DIONYSOS, are made up of a photometer, which measures absorbances, and of specific reagents for each analyte. Simply add the sample to the reagents to obtain a compound whose absorbance measured at a given wavelength is proportional to the concentration of analyte under consideration. This proportionality allows you to construct calibration lines from reference materials of known concentration (calibrator), which can later be used to deduce the concentration of the analyte in the sample.

FT-NIR systems working principle

The interaction of light matter is also the basis of these systems, but less energetic (infrared) wavelengths are used compared to enzymatic (UV-Visible) methods.

Infrared electromagnetic radiation vibrates the bonds of organic molecules, so that different functional groups within the individual molecule (eg -NH2 or -COOH) are excited by different frequencies. If we scan the absorbance of a pure substance in all the wavelengths included in a given range, we will obtain a characteristic graph of the substance (spectrum). If we compare the spectrum of a sample containing multiple substances, it is possible to identify them by comparing the spectrum obtained with those of pure substances and, again through comparison, to determine their concentration.

However, the spectra obtained with the classic IR spectrophotometers do not offer enough technical characteristics to be able to carry out a quantitative analysis. A more modern technique, called the Near Infrared Fourier Transform (FT-NIR), solves many of the problems of classical IR spectrophotometry: it has extremely fast times, a high signal-to-noise ratio, and a much higher resolution, which allows a better distinction of the various organic functional groups.

FT-NIR spectrometers produce a signal, called an interferogram, that contains the absorbances at all analyzed frequencies encoded within it. It is produced through a light signal that is split into two halves; one half will have a fixed length, while the other will vary in length thanks to a movable mirror. When the two signals recombine, they will produce positive or negative interferences according to the different lengths. This new signal is passed through the sample and then to a detector. The signal can be measured very quickly, performing several scans per second. The interferogram is then processed through a mathematical process called the Fourier transform, which gives rise to the spectrum of the sample under examination. At this point, the sample spectrum is compared to a database of hundreds of different spectra from various samples in which the components of interest have been determined. The concentration of the test sample is statistically estimated by comparing it with the database. In other words, the results obtained are not actually measured, but are obtained through statistical analysis.

Pros and cons

Many of the enzymatic methods have been included among the official methods of the OIV, while the FT-NIR, which cannot be calibrated with reference standards such as enzymatic systems, does not meet the requirements to become a reference as it is not properly a measurement method. This does not mean that the FT-NIR methods are not valid, but that they cannot be used to issue certified values.

FT-NIR systems are extremely faster and deliver a set of results in just a few seconds. Enzyme systems are slower and require incubation times of the order of 5-10 minutes to complete reactions and proceed with measurements.

Enzymatic systems are «open» in nature and the entire measurement process is visible and monitored; the various methods must be calibrated and controlled, which requires a certain participation of the operator who can intervene at any time to correct problems (turbidity of the samples, for example). In contrast, FT-NIR systems are “closed black boxes” in which it is not possible to intervene in the measurement, correct the calibration or detect interference that modifies the optical signal. The signal processing and the calculation of the results is entrusted to the software, which in turn relies on a database that is useful only to the extent that the sample is perfectly represented in the data set used.

Enzymatic methods have much wider measurement ranges than FT-NIR, and are much more sensitive. In fact, the FT-NIR is unable to adequately determine concentrations below 0.2 g/L, approximately since the signal-to-noise ratio is very low. Adequate sensitivity is relevant for the winemaker in certain processes, such as the end of alcoholic fermentation or the beginning of malolactic fermentation, in which it is necessary to recognize extremely small amounts of analyte and identify the right moment to act.

Enzyme reagents are highly specific, so that they only recognize the molecule of interest, being able to distinguish between chiral molecules. For example, it is possible to distinguish between D- and L- stereoisomers, whereas with FT-NIR you will always obtain only the sum of the two since both molecules have the same chemical structure and bond arrangement.

Another important difference between the two systems is their scalability: an FT-NIR system offers simultaneous results for a defined set of analytes. Although FT-NIRs do not require consumables or reagents, this set of analytes cannot be modified or reduced, but cannot be expanded either, since the result is generated from a mathematical function that incorporates them as parameters; therefore, if the analyte is not included in the definition of said function (which in turn is generated by the database used), it cannot be added later.

With enzymatic systems, on the other hand, since they are composed of an instrument (manual or automatic photometer) and reagents (each reagent is specific for a single analyte), it is possible to choose which analytes to dose and not necessarily all of them must be used together. This leads to complete freedom in the use of the enzyme system, which is much more flexible for the specific and seasonal needs of the winery.

The FT-NIR systems exploit very advanced technologies and very powerful software, which determine a very high cost for instrumentation and, although little is required of the operator in terms of daily maintenance, they require periodic maintenance by specialized personnel with high costs. On the other hand, enzyme systems, even automatic ones, take advantage of consolidated technology that has lower costs, both initial and maintenance.

Statistical estimation of concentration against a database
Quantitative measurement of analytes by specific enzymatic reactions
It is only possible to adjust the result by comparing with other analysis methods
Calibration with reference material
Very easy to use: just push a button
Requires some user training
They are closed «black boxes» that do not allow intervention
They are open systems that allow action
Very expensive, but do not require consumables or reagents
Economical, but require consumables and reagents
Time to results
Results in less than a minute
Results between 5 and 10 minutes
Little, but can only be done by the manufacturer due to its complexity (high cost)
Daily and simple maintenance by the user, and periodically by the manufacturer, of low complexity (low cost)
Sensitivity and accuracy
Very sensitive and reproducible methods
Not possible
Official OIV / AOAC
Not approved
Quite a few official OIV methods (not all)


Enzyme systems and FT-NIR are totally different systems and a direct comparison between them is not possible, except when we refer to specific process needs. Most often, the two systems are used together, amplifying the advantages and eliminating the disadvantages. In many warehouses, during periods of intense work, such as harvesting, FT-NIRs are used to process numerous samples in a short time, obtaining sufficient initial results for this purpose. Later, however, the use of enzyme systems allows the results to be verified with greater precision and accuracy and a greater guarantee of data security. Additionally, enzyme systems can be used as a simple, inexpensive, and safe method to verify and calibrate FT-NIR systems.

For more than 10 years, Sinatech’s commitment to the winemaker has been working side by side to provide the most appropriate analytical solutions to the control and monitoring of the winemaking process. Automated methods easily adaptable to any work routine, with a personalized advisory team to help you quickly and smoothly implement.

Sinatech: TeamWork.


Calibration an control guide 2
Calibration an control guide 2

A control sample (or control, simply) is a tool that allows us to verify whether a given measurement has been performed correctly, comparing the result of said measurement with the expected value for said control. In addition, if control is sufficiently similar to the samples, we can extrapolate that they will behave identically, which allows us to assess the quality of the measure through statistical treatments.


The purpose of the analysis laboratories is to provide information about the composition of the samples, which, in turn, serves to make decisions. It is important, therefore, that such information is truthful and appropriate to its purpose, so it will be necessary to establish criteria that indicate the degree of reliability of the measures taken.


It should always use to verify that the measurement conditions are still valid. Although maximum certainty is obtained by checking before the analysis starts, along the analysis process and at the end of it, usually is enough to carry out the control at the beginning of the measurements so required corrections can be performed before making the measurements on the samples.

The system must also be controlled every time a new calibration is done, and especially if there is a reagent change involved.


The repeated measurement of the same control allows obtaining valuable information about the conditions in which our system operates, including accuracy and precision of the procedure.

Information does the control provides 2

Accuracy indicates the proximity between the measured value and the reference value of the sample (values dispersion); precision (also referred as trueness) indicates the degree of proximity of several repeated measures around an average value (bias from target). A precise measurement is not necessarily accurate, and an accurate measurement is not necessarily precise. The results will have an error that will depend on the inaccuracy and a bias that will depend on the precision of our procedure. Both should be kept under control, whether they are unpredictable (random error) or if they are directly related to our measurement procedure (systematic error).


The random error is the one that appears due to the variability inherent in the analysis tools. It is inevitable and the goal is to reduce it as much as possible. Possible sources of random error are the lack of homogeneity of the sample, the variability in the dispensation, the oscillations of the light source… Due to its unpredictable nature, the only way to reduce it (as you can not eliminate it) is to monitor potential sources of error and act on them. For the same reason, the way to detect it is by means of successive measurements of the same sample (that is, a control sample): a high random error is observed as a lack of accuracy (i.e, dispersion above the expected values).

The systematic error appears when the values ​​obtained deviate in a specific way from the real value of the sample. In this case, we must look for the nature of this deviation in the measurement procedure. It can be both absolute (for example, an interference introduce a constant bias along all concentrations) or proportional (deviation increase as per analyte concentration). Unlike in the previous case, the systematic error can (and should) be eliminated. A common cause of systematic error is the loss of the calibration status due to the natural deterioration of the reagents over time. In that case, we observe a progressive deviation along time of the value obtained from the control with respect to the expected value to the point that said deviation becomes unacceptable. Another common case of systematic error occurs when calibrator, controls and samples show significant behavioural differences with respect to the reagents (matrix effect). These differences are corrected by assigning a value to the specific calibrator for the reagent to compensate for this effect, which means that exchanging calibrators and controls with reagents from different suppliers is, in general, a bad practice as said compensation is not accounted for.

It is important to note that in both cases it is not the particular measured value of the control material that triggers the alarms since this measure is itself subject to random error, but the analysis of successive measures over time that give us such information. Most systems have specific graphic tools that greatly facilitate the interpretation of control series in a simple way, even without additional statistical or metrological knowledge. Some of the most used are:

Levy-Jennings graphs: They represent the successive measures against their deviation from the expected value, marking limits at 1, 2 and 3 times the standard deviation of the measure. It is very easy to detect when these deviations cease to be random, present trends or are simply much greater than what is statistically acceptable.

Levey-Jennings Graph

CUSUM Charts: Represents each successive measure against the cumulative sum of the deviations from the expected value obtained so far. In an ideally random series, this sum will be close to zero (as negative and positive bias will be compensated), while in a series that shows a trend with oscillations (i.e systematic positive or negative bias), this sum will increase its value.

Cusum chart of data

The proper use of controls is the best guarantee to ensure the accurate and precise results necessary to guarantee the entire winemaking process with guarantees.

For more than 10 years, Sinatech’s commitment to the winemaker has been working side by side to provide the most appropriate analytical solutions to the control and monitoring of the winemaking process. Automated methods easily adaptable to any work routine, with a personalized advisory team to help you quickly and smoothly implement.

Sinatech: TeamWork.




Calibration is the process by which we determine the intensity of the signal we measure when we analyze a sample of known concentration. The problem samples will be compared against that result by means of a calculation of proportions that will return the concentration of the sample in the same units in which we have expressed the calibrator.

The control (or internal control) is a procedure by which we verify that the calibration is valid. To do this, we use a sample of known and stable concentration over time (which can be a proprietary sample conserved especially to serve as a control, or a commercial control for which, under the calibration conditions we want to use, we verify that the result obtained is within the range of expected values.

It is important not to control with the same sample with which it is calibrated, since we will always obtain a «correct» result regardless of its functional status. Controls and calibrators must necessarily be independent and different samples.


Calibration should be carried out when there is a possibility that the reagents’ behaviour has changed and the results are not comparable to those that were available so far. A calibration should be performed if:

  • Reagent kit change: The new kit may have a different state of preservation, or be from a different batch.
  • Change of working reagent: Although the reagent comes from the same kit, the new working reagent is different from the previous one and could have some different characteristic (for example, the reaction blank value in the case of R1 or the amount of enzyme of R2).
  • When recommended after opening: Open reagents are degrading due to exposure to air, or due to the effect of ambient temperature. Manufacturers can define periods for which calibration is maintained within reasonable values; beyond that time, the risk of the reagent being different in its characteristics increases and a new calibration that «zeroes» the system is recommended.
  • When there is evidence that the controls do not give the expected value: Using controls within all the work series allows us to detect any alteration of the reagent if the control deviates from the expected value (for example, beyond 15% per above or below the central value). There are rules to follow the evolution of control values ​​that indicate the need or not to recalibrate the system.
  • When the values ​​of target and/or of increments of absorbance are significantly different from the previous results: A signal of deterioration of the reagent is obtained when the value of target is very different, or the variation of absorbance in the reaction is clearly less than expected.

If none of these circumstances occur, it is very possible that calibration is unnecessary.


As a general rule, the more the test sample resembles the calibrator, the more reliability we will have in the result. However, there are factors specific to the sample that are impossible to replicate in a calibrator, mainly because the composition of the sample is more complex than that of a calibrator.

One of the most common is the colour of the sample, for example due to a high concentration of polyphenols. The usual calibrators do not have a high colour intensity and are therefore free from interference that does exist in the sample. Using bleaching procedures can partially solve this problem only if we are sure that it does not affect the parameter to be measured.

Another element of frequent interference in the samples is the presence of particles (turbidity), which introduces unwanted light scattering phenomena. Its presence can be reduced by filtration and/or centrifugation.

Finally, one of the most difficult external factors to detect, but which can be critical in many parameters, is the water used in the system (such as water to wash, to dilute, etc.). Water is a theoretically neutral component but it can actually contain concentrations of ions (calcium, magnesium, phosphorus, nitrates, chlorides…) that are relevant for the analysis. Be sure to always use a reliable source of distilled water in both calibration and sample analysis and dilution.

Proper management of the calibration status saves unnecessary recalibration costs or second analysis, while ensuring the accuracy of the results.

  • Cod. SY2100


    Multiparameter calibrator
    Glucose, Fructose, Acetic, L-Lactic, L-Malic, Citric, Gluconic, Glycerol, Ammonium
    Presentation: 1 x 10 mL
  • Cod. SY2100-RTU


    4 levels multiparameter calibrator
    Glucose, Fructose, Acetic, L-Lactic, L-Malic, Citric, Gluconic, Glycerol, Ammonium
    Presentation: 4 x 5 mL
  • Cod. SY2108


    1 level - Lim. Sup. Linearity
    Amino acids
    Presentation: 1 x 5 mL
  • Cod. SY2109D


    1 level - Lim. Sup. Linearity
    Presentation: 1 x 5 mL
  • Cod. SY2110


    1 level - Lim. Sup. Linearity
    Presentation: 1 x 5 mL
  • Cod. SY2111


    1 level - Lim. Sup. Linearity
    Presentation: 1 x 5 mL
  • Cod. SY2112


    1 level - Lim. Sup. Linearity
    Tartaric acid
    Presentation: 1 x 5 mL
  • Cod. SY2115


    1 level - Lim. Sup. Linearity
    Calcium salt
    Presentation: 1 x 5 mL
  • Cod. SY2116


    Presentation: 1 x 5 mL
  • Cod. SY2118


    1 level - Lim. Sup. Linearity
    Copper salt
    Presentation: 1 x 5 mL
  • Cod. SY2122


    1 level - Lim. Sup. Linearity
    Iron salt
    Presentation: 1 x 5 mL
  • Cod. SY2124


    1 level - Lim. Sup. Linearity
    Gallic acid
    Presentation: 1 x 5 mL
  • Cod. SY2125


    1 level - Lim. Sup. Linearity
    Potassium chloride
    Presentation: 1 x 5 mL
  • Cod. SY2128


    1 level - Lim. Sup. Linearity
    Sucrose, glucose, fructose
    Presentation: 1 x 5 mL
  • Cod. SY2130


    1 level - Lim. Sup. Linearity
    Tartaric acid
    Presentation: 1 x 5 mL

For more than 10 years, Sinatech’s commitment to the winemaker has been working side by side to provide the most appropriate analytical solutions to the control and monitoring of the winemaking process. Automated methods easily adaptable to any work routine, with a personalized advisory team to help you quickly and smoothly implement.

Sinatech: TeamWork.



The final process in the development of grapes leads to a remarkable change, both physical and metabolic, which is very important to monitor to ensure the optimal time for harvesting.

The berries are small and green in the early stages of development. Progressively, the water and sugar content increases and the grapes increase in weight and volume until the starting point of the physiological maturity process is reached, the winter. At this time the growth stops and a series of metabolic changes occur which will provide the characteristics sought in wine production.

The first change is that of the color of the grapes, which goes from green, associated with a high concentration of chlorophyll, to a purple-blue tone (for the red varieties) or yellowish green (in the white varieties) due to the increase of polyphenols (flavonoids, anthocyanins and tannins) in the skin and decrease in the pulp. This change occurs quickly for each berry (in one or two days), but not uniformly in the bunch or in the vineyard (which will completely develop the color in about 10-15 days, depending on the variety of climatic characteristics). The bloom, a whitish and waxy layer that acts as a protector and fixative of yeasts, covers the grapes. From this moment, the grapes will need between 35 and 55 days to complete their maturation and reach the optimal harvest time.

The disappearance of chlorophyll is also accompanied by significant metabolic changes in grapes which, in general, we can interpret as a process of alcoholic maturation, in which fermentable sugars are accumulated (which therefore influence the alcoholic degree that the wine will reach after fermentation), and a process of phenolic maturation, in which anthocyanins and tannins are fixed on the inner part of the peel (and will have an effect on aromas and astringency). It must be considered that both processes take place simultaneously, but not in parallel, so an optimal level of sugar and acidity may not correspond to the optimal level of polyphenols and vice versa. It is based on the point of equilibrium between these two processes, called technological or industrial maturity, that the oenologist decides the most suitable harvest time for each variety and growing conditions.

Phenolic maturation involves the activation of the phenylalanine-aminoliasis enzyme (PAL) by heat, light and the action of abscissic acid. This enzyme is involved in the synthesis of phenolic compounds starting from the degradation of phenylalanine and tyrosine to cinnamic acid and is present exclusively in the skin cells and in some parts of the pulp. The process takes place through three phases: a rapid accumulation in the skin cells, which causes the color of the grapes to change; a phase of stagnation, in which they reach their maximum concentration; and finally, a decreasing phase, in which the anthocyanin concentration begins to decrease. It is at the moment when this decrease begins that the complete phenolic maturation is reached and, from this moment, over-ripeness would provide notes of cooked or candied fruit.

The most common procedure to determine the level of phenolic maturation is based on the acid extraction of the content of polyphenols (or anthocyanins) at pH 3.2, simulating the conditions that occur during fermentation while respecting the integrity of the peel, and pH 1.0, very much more aggressive, in which the entire phenolic content is released (Glories method), so that the smaller the difference between the two values, the greater the degree of phenolic maturation. Measurement of polyphenols in both cases uses a colorimetric method (Folin-Cicalteau).

At the beginning of the alcoholic maturation, the grapes contain about 10-15 g of sugars per liter of must, mainly in the form of glucose (85% of the total). During alcoholic maturation, the concentration of sugar increases to 150-200 g per liter of must. This increase is also accompanied by isomerization of glucose to fructose, which leads to a concentration of fructose in the mature grapes of more than 95% of the total. This accumulation is not a product of the photosynthetic activity of grapes, since, as mentioned, chlorophyll disappears, but is a consequence of the contribution of the rest of the plant that mobilizes sucrose (the disaccharide formed by glucose and fructose, which is sugar main in the leaves) in the berry, where it is dissociated into fructose and glucose. Maturity is reached when the total concentration of sugar is sufficient to guarantee the desired alcoholic strength in the finished wine. At this point, the glucose / fructose ratio is practically equivalent ([Glu]/[Fru] = 1), but glucose will be consumed in cellular respiration, lowering the ratio to values ​​of about 0.92-0.95 at the time optimal harvest. Also the acid content of the grapes evolves considerably at this time, both in its concentration and in its composition. At the beginning of winter it has its maximum value, around 10-8 g/L and consists mainly of malic and tartaric acid, which represent more than 90% of the acids. From this moment, the acidity is reduced by the metabolism of the berry itself, above all due to the consumption of malic acid which is transformed into glucose. At the beginning of the harvest, the total acid content was reduced to 4-6 g/L with the prevalence of tartaric acid.

Given the importance of sugars and acids, the winemaker’s main decision is to establish the right relationship between them. One of the most used technological maturity indices, the Cillis-Odifredi index, relates the sugar content and total acidity (total sugars in 100 mL of must divided by grams of tartaric acid per liter of must). It is considered an appropriate time for harvesting if the index is between 3 and 5, depending on the grape variety and the type of wine desired.

The quality of the wine begins in the vineyard and choosing the right time for the harvest is the first critical decision that the winemaker must make. Sugars, acids and aromas will be, among others, fundamental elements of this decision. Having practical and reliable tools as a guide is undoubtedly essential for achieving the intended goal.

Kit for evaluating the technological maturity of grapes
SY2404 · Glucose+Fructose
SY2428 · Total Sugar
SY2402 · L-Malic-Acid
SY2412 · Tartaric Acid
SY2430 · Total Acidity
SY2424 · Polyphenols
SY2414 · Anthocyanins
SY2416 · Catechins

For more than 10 years, Sinatech’s commitment to the winemaker has always been working side by side to provide the most appropriate analytical solutions to control and monitor the winemaking process. Automatic methods easily adaptable to any work routine, with a personalized consulting team to help you implement it quickly and without problems.

Sinatech: TeamWork.