The Research of Constituent Clay-minerals of Qvevri and its Influence on Wine

2019-09-09
77 ნახვა

LEPL Iakob Gogebashvili Telavi State University

With the right of manuscripts

Gia  Gamtkitsulashvili

The Research of Constituent Clay-minerals of Qvevri and its Influence on Wine

To obtain the academic degree of Doctor of Food Technology

Submitted of Dissertation

A b s t r a c t

         2018        

General Description of the Work

Research rationale.The Authorities of Georgia have prioritized viticulture-winemaking field and its development. Starting 1990s, after restoration of independence and legalizing property ownership forms, the new system enabled private owners and companies to accept more challenges and establish new technologies in production. The competition gradually outlined Qvevri wine, as almost forgotten product. However, Georgian farmers have always used Qvevri as a wine vessel.

Georgia is homeland of wine and this theory is proved by a lot of historical materials and archaeological exponents. Clay Qvevri vessel unearthed in the village of Shulaveri is one of the similar proofs. This artefact is about 80 centuries. Therefore, UNESCO has recognized Georgian technology of wine fermentation in Qvevri and included it in the list of the world’s intangible cultural heritage.

Kakhetian wine-making technology implies the sweet alcoholic fermentation on dregs in Qvevri (with or without a stem) and a delay with it for 5-6 months in the closed areas.  We know that quantity of mineral substances accumulated in the sweet grapes is directly dependent on the stock of the mineral substances in the soil. After the grapes mechanical processing, the dregs become rich in mineral substances, so, unlike to European technology, in case of Kakhetian wine making, along with yeasts they are actively participating in sweet alcoholic fermentation and wine maturation processes, as well as in the microbiological and physical-chemical transformations taking place in wine making process, which ensures a  low acidity and solidity  of Kakhetian wine as a result of   high content of extracts and tannins. Such a wine is rich in mineral substances and is distinguished with medicinal value and positively affects the health of the consumers.

Kakhetian wine is unique in terms of organoleptic and deserves a high assessment from the winemakers’ side. In addition, it is known that the composition of mineral substances in wine   is affected by the vessels, from the walls of which are migrating the mineral elements. As we can see, the existence of mineral elements and the amount of their value in wine is very important, it may depend on the composition of the soil, the sweet and its concentration on dregs and of course on  the vessels in which the wine is made. In this respect, the most unique wine-vessel is Qvevri, which is made by recycling and burning the natural raw material of the earth- clay minerals. Based on the above, it is very important to study the structure of primary raw materials, solid and plastic clay minerals from the various fields of Georgia and determine the amount of elements in it. What is more, the determination of the physic-chemical characteristics of the vessel walls recycled from the same clay mineral sand burned at different temperature and the study of different Qvevri’s influence on the quality of the wine produced from one and the same grapes is vital.

Objective and tasks of the research. Objective of the research was to thoroughly study primary clay minerals, extracted from deposits existing in various Qvevri production districts, as well as Qvevri building materials and Qvevris made of these building materials (mineralogy, number of elements, Qvevri furnacing temperature) and to explore wines fermented in this Qvevri on the structure of mineral elements, chemical structure and tasting indicators. 

Based on the above-mentioned the research work task was to:

1.Study the Qvevri building materials, chemical and physical properties of Qvevri mineralogy structure.

2.Determination of the number of mineral elements in must and wines fermented in different Qvevri in different ageing periods.

3.Study a migration of mineral elements in the must and wine from Qvevri made of clay minerals extracted from various deposits.

Scientific innovation of the work. For the first time we explored mineral structure of primary clay minerals  of Qveveri building materials extracted from various deposists, Qvevris made of the same materials, clay fragments furnaced jointly with Qvevri, as well as physic-chemical properties and differentiating properties.

It was found out that:

1.Qvevris differ from each other by drying and furnacing temperature; mineral structure and production technology;

2.Physical and chemical analysis of wine and tasting indicators have proved a rise in mineral substances, taste signs of Wet Clay and saltiness tones in wines of those Qvevri, which were furnaced at comparatively low temperature – below 800°-850°C. This factor has influenced organoleptic properties of wine and it worsened wine quality.

Practical importance of the work. The research work has showed that in the process of making Qvevri, mineral structure of Qvevri building material should be explored. Qvevri furnacing top margin temperature must be 950°-1050°C. Instruction and recommendation is given to National Wine Agency to prepare Qvevri making technological instruction and standard. Qvevris made of this technology will enable to make high-quality, competitive Qvevri wines with different standards and high-organoleptic properties. 

Economic effect. Based on the thesis experiment, besides other factors, quality of wine fermented on dreads in Qvevri is preconditioned by Qvevri quality and this signifies: proper selection of Qvevri building material, thorough management of Qvevri production technological process and protection of optimal temperature for drying and furnacing.

Based on the experiment and according to tasting indicators, number of mineral substances excessively grows in Qvevri wine fermented in Qvevri made by violation of technological processes (mainly Qvevri furnaced on low - 800°-850°C temperature), tasting of Wet Clay and saltines tones are evident and this makes influence on organoleptic properties of wine and worsens wine quality, makes negative effect on consumers and all these factor effect wine sales.

Market price of Qvevri high-quality wines at trade outlets range from 20 GEL to 30 GEL, while prices at local trade outlets range from 14 GEL to 20 GEL. The prime cost of one bottle of wine (0,750ml) is 4.65 GEL, which gives economic effect for production.

Reliability of received results. We have extracted primary clay mineral from deposits nearbyQvevri masters, who have made research Qvevris.The research works have been carried out by modern methods on high-sensitive equipment. Wine samples were tasted by the central tasting commission of Georgia at National Wine Agency (see the attached minutes).

Approbation: results of the research works were annually (2014-2018) discussed at meetings of Telavi State University Faculty for Agrarian Studies

Publication. 3 rsearch works were published on key results of this thesis. The research materials were mentioned on 2 international conferences.

Thesis structure and volume: The thesis consists of: general description of the work, literary discussion, experimental part, conclusions and Annexes. Thesis consists of 132 pages, which contains 25 chart and 17 pictures. The list of the used literature comprises 111.

Experimental Part

Research Subjects and Methods

To adjust our research works to Qvevri production, we, jointly with selected masters, extracted primary raw material from immediately deposits. The raw material was processed; Qvevris were made and furnaced by the same technological procedures used today by the best Qvevri production masters. In total were make 10 pots from Maqatubani(Satsable), Srosha (Satsable), Atsana, Tkemlovana and Vardisubani clay materials, which were placed in special researching cellar of company Twins Wine House in Napareuli. Here are represented only 4 Qvevri’s pattern results. Thus, we have received the following samples and the research Qvevris and they were numbered:

Maqatubani (Satsable):  №1 - plastic material (Akalo); № 2 – non-plastic material (Thiri); №3 – mixed clay material; № 4 – clay furnaced jointly with Qvevri; № 5 –Furnaced Qvevri of Maqatubani.

Atsana: №6 - Plastic material (Akalo); № 7 – the river Rioni sand; № 8 – mixed clay material;  №9 - clay furnaced jointly with Qvevri; №10 - Furnaced Qvevri of Atsana;

Tkemlovana: №11- Plastic material (Akalo); №12 – non-plastic material (Thiri); №13 - mixed clay material; №14 - clay furnaced jointly with Qvevri; №15 - Furnaced Qvevri of Tkemlovana;

Vardisubani:  №16 -Plastic material (Akalo); №17 –the river Alazani sand;  

№18 - mixed clay material; №19 - clay furnaced jointly with Qvevri; №20 - Furnaced Qvevri of Vardisubani.

Research patterns of clay materials were numbered locally. They were placed in special packs and sent to the research laboratory of Georgian Technical University department for mineralogy and geology. A month later we sent clay materials furnaced jointly with Qvevri with the due numeration to the same laboratory.

These Qvevris were placed in the village of Napareuli at the research wine cellar specially built on the territory of Twins Wine House company. Together with these Qvevris, non-Qvevri neutral vessels of cylinder shape of the same capacity were placed in the ground, which were called the control neutral vessels and above the ground one more neutral (not Qvevri) vessel was placed which was called a reserve neutral vessel, from which after alcoholic fermentation completion, the test Qvevris and vessels were replenished.

Each research Qvevri and vessels were numbered:

№21 - Neutral vessel; №22 - Auxiliary neutral vessel.

Thus, we have received six research vessels: Four main research Qvevris and two neutral Non-Qvevri vessels. At the same time, we have taken cylinder sections from walls of our research Qvevris (5, 10, 15, and 20) and usable Qvevris made in Vardisubani in 1980 and the following numeration was given to them:

№23 -cylinder section of Makatubani Qvevri

№24 -cylinder section  of Atsana Qvevri

№25 -cylinder section  of Tkemlovana Qvevri

№26 -cylinder section   of Vardiubanio Qvevri

№27 -cylinder section   of Vardisubani Qvevri (1980)

In the same period, we created one more research Qvevri and its making technological process radically differs from technology of making Qvevris. Namely, this Qvevri was made by technology for making high-strength ceramic vessel and it was furnaced in hermitized electric furnace for 24 hours at temperature 1200°-1500°C.

For the purpose of our research works, we have arranged ordinary consumer clay pitcher furnaced at low temperature. From these two research things we have taken required samples. Thus, we received two more additional research samples:

№28 – ceramic Qvevri fragment; №29- Pitcher fragment.

Rkatsiteli grapes picked in the vineyard owned by Twins Wine House Company in the village of Napareuli located in Napareuli microzone in Kakheti Region was selected as research subject.

Our research wine was prepared through joint fermentation of the must and dregs without stalks with 6-month stay. Stalks were removed, because, according to the due literature, mineral substances with high concentration in the grapestalk demonstrate migration to the wine. In our case, we want to outline the influence of Qvevri mineral substances on wine. In our case, we want to highlight the impact of mineral substances of Qvevri on wine. Mineral substances existing the structure of grape pip may perform negative role on accuracy of our research works.

The Primary processing of grapes were squeezed in the rolling pressure. As a result, the stalks were removed and dregs jointly with the must moved to the research Qvevri and vessels. In the same period, primary analysis was carried out on the must and its sugar content was determined. The control must was taken in the special vessel, which was placed in the refrigerator containers and sent to the research laboratory to identify the volume of mineral elements in it. Yeast was added to the Qvevris for ensuring stable alcoholic fermentation. The alcoholic fermentation lasted 12 days and this is characteristic to Qvevri wines. After analyzing the completion of alcoholic fermentation in Qvevri and vessels, were take new wine material researching examples. For 7 days test Qvevris and vessels were kept in closed, but unsealed condition. After that Qvevris and vessels were replenished with wine materials of the first fraction from the reserve neutral vessels.. After this, all of them were sealed. The next samples were taken after three months and 6 months after sealing Qvevris.

Thus, we received the following research samples:

Pattern 0 – Control must

Maqatubani Qvevri №5 : Sample 1 – new wine; Sample 2 – wine of 3 months; Sample 3 –  wine of 6 months. Atsana Qvevri №10.: Sample 4 – new wine;  Sample 5 - wine of 3 months;  Sample 6 – wine of 6 months; Tkemlovana’s Qvevri №15:  Sample 7 - new wine; Sample 8 - wine of 3 months; Sample 9 – wine of 6 months.

Vardisubani Qvevri №20: Sample 10 – new wine; Sample 11 – wine of 3 months; Sample 12 – wine of 6 months.

Neutral Control Vessel №21: Sample 13  - new wine; Sample 14 – wine of 3 months;  Sample 15  – wine of 6 months

Auxiliary Neutral Vessel №22 – Sample 16 - new wine

Samples were placed in wine bottles, sealed, numbered and sent to the wine laboratory “Wine Laboratory” LTD.

Analogical studies were continued in 2017 too.

Raw materials extracted from the deposit such as primary clays, Qvevri building clay materials, furnaced clay material and Qvevri clay test samples were explored at the Georgian Technical University department for applied geology for identification of physio-chemical characteristics and mineralogical structure.

The samples were subjected to:

.1.Petrographic analysis through polarized microscopy. As a result, we have identified their structure and mineralogical composition.

2.X-ray fluorescent analysis through spectrometer edx3600b determined the structure and volume of elements.

3.Roentgenography analysis has determined exact number and phases of the prevailing minerals.

Key parameters of quality indicator were determined in the control must taken by us and test wines samples through methods of analysis of must and wine existing in the literature and though methods determined by International Wine Organization.

For the purpose of definition of mineral substances and their volume in control must and research wines, we have used plasma-emission spectrometer. The method for measuring metals by this spectrometer is based on measurement of intensity of spectral waves of those elements, when they are ignited in the process of adding samples of these elements into instruments (in the form of aerosol). In this moment, detector reflects intensity. Calibre graphics ensure connection between emission intensity of elements and their concentrations.

This method ensures a fixation of the measurement results with minimal errors.

Preparation of micro elements of samples is to prepare standard and calibre solutions.

To measure the sample, we should select analytical wave lengths in advance, which is different in all elements.

Prior to starting operation on spectrometer, we should check the pressure, turn on the plasma, add the sample in the spray system; the samples are sprayed and get into the plasma. After the measurement, concentrations will be reflected in mg/l dimension. 

Research of Qvevri and its building clay minerals, physical chemical properties and mineral substances

It is especially important for Qvevri-making the right selection of mine fields, extracting raw material, its processing, Qvevri-making and furnacing temperature.  

For making high quality Qvevri it is important to find right mine field, extracting raw material, processing,  technologic building process of Qvevri, building the furnacing stove and furnacing procedures on limited temperature. Beside that it is important in Qvevri making process the fractal granulometric sizes of minerals in primary raw material which are extracted from minefield. Plastic clay minerals are smaller than mechanical contaminant substances. 

Generally clay minerals are found with high, medium and low plasticity. As much as there is pure particle quantity of clay minerals in raw material and less mechanical admixtures more plastic is building material of Qvevri, though most or the whole clay – in case of minimal quantity of mechanical minerals- during the Qvevri making, drying and furnacing process it can be deformed and slided down.

Because of the exceptional tasteful qualities of the Qvevri wine, winemaking specialists have suggested that Qvevri must have influence on the quality of wine since it is not a neutral vessel.

Considering upper mentioned our research aims to examine and learn mineral consistency, physical-chemical qualities and furnacing temperatures of collected samples (primary clay mineral material, building material, fragments of clay furnaced with Qvevri, cylindrical cuttings of Qvevri, fragments of ceramic Qvevri and jar) represented by ourselves. It was conducted examination beginning from the 1st ending to the 27th  samples petrographic, roentgen phase and roentgen fluorescence central analysis. As it is knownmostly there are represented Kalium, Magnium, Natrium and Calcium in soil and in mineral materials of wine’s ash as well, that is why we decided to inspect those four elements – Kalium, Magnium, Natrium and Calcium.

It defined minimum consistency (quartz, feldspar, mica, pyroxenes, amphibolies) and their fractal granulometric sizes of connecting material (clay minerals, iron oxides, hydroxides and others). It was found out also essence and some quantity of mineral element’s phases, what gave us possibility to define furnacing temperature of samples. According to the results in the samples of the primary raw material and in the fire resulted samplesmineralogical consistency and quantity of elements is kept almost unchanged  (see table). These results give us possibility to conclude that mechanical processing of primary raw materials and their furnacing procedures don’t change mineral consistency and quantity of elements in it, thus we started to conduct observations and evaluation of analysis results of the next samples:

№4 the limestone and clayeyextracted from minefield of Makatubani (Satsable) and from them produced and furnaced fragment of clay.

№9 limestone extracted from minefield of Atsani and river Rioni’s sand processed and furnaced fragments of clay.

№14 limestone and clay extracted from minefield of Tkemlovana and from them proceeded and furnaced fragments of clay.

№19 limestone extracted from minefield and sand of river Alazany proceeded  and furnacing fragment of clay.

№23 Cylindrical section of Qvevri

№24 Cylindrical section of Atsani’s Qvevri

№25 Cylindrical section of Tkemlovana’s Qvevri

№ 26 Cylindrical section of Vardisubani’s Qvevri

№27 Cylindrical section (1980 year) of Vardisubani Qvevri

№28 Ceramic fragment of Qvevri

№29 Fragment of consuming jar.

Given illustrations of microscopic research samples and rentgenophasic diagrams can be seen in dissertation.

Illustration of №4 sample is provided in dissertation –  produced and furnaced fragment of clay, which was extracted from minefield of Makatubani (Satsable). The sample is reddish fragment on microscopic level,  it is remarkable on surface of its different size and color additions, doesn’t react on hydrochloric acid. Under the observation of magnifying glass  it is porous, but doesn’t absorb water actively.

In the microscope binding i.e. essential mass is represented as an amorphic clayey mass and a lot of supplementary i.e. broken pieces of mineral fragments and layers with different sizes, mostly dominating by few minerals, which have various size and shape. We find there also some pieces of layers quite seldom. Mostly  in mineral consistency prevails Plagioclase, what alwaysis replaced by secondary minerals (clay minerals, Sericite), sometimes it is remained polysynthetic and rarely grains of amphiboly.

Pieces of layers arerelatively smaller and generally are represented as fine-grained feldspars of Quartz-field with its broken down layers. Mostly broken pieces are so replaced that only its shapes are left.

According to Rentgenophase analysis piece of Qvevri’s sample which were made bylimestone and clayey materials extracted from Makatubani (Satsable) quarry is consisting with following phases: Quartz 7-10%; Ca-Na feldspars 20-25%; Amphiboles are represented only as traces. The rest is dispersal rentgenoamorphic phase. The Qvevri possibly is furnaced on 950°-1000°C. 

According to the research we find out that in primary extracted raw materials from minefields of Vardisubani, Tkemlovani, Makatubani, Atsani buildinglayer and admixture chemical elements consistensy are different to each other.

Quality of Qvevri depends on primary raw materials – clay mineral consistency, quality of processing building material, on drying and furnacing procedures. Furnaced minerals in the Qvevri have small size porous and their sizes and quantities define level of oxide receptiveness. In Qvevri making process used raw materials including mechanical minerals: Quartz, feldspar, (Plagioclases, feldspar of K), Pyroxenes, Amphiboles are sustainable under the exposure of 950°-1000°C temperature fire, though they can be changed structurally. After furnacing of Qvevri its walls are still remaining  porous. The essence of pores and their size depends on mineral constituency of raw materials, their granulometric sizes and furnacing temperature. Respectively large sizes of pores are caused by nesting unhospitable microbes and high amount of oxide inflow, what appears mal-effective for wine and its fermentation process. Mechanic admixture of mineral quantity, nature and size has its own  certain importance on pores. As we found out from conducted researches, the Qvevris vary according to raw materials extracted from different quarries by their mineral consistency and making technologies, especially with furnacing procedures.(The temperature for our Qvevri samples was fix from 750°C to 1050°C) As a result of our research we know that exposure on fire of Qvevri was from 950°C to 1000°C  temperature, which gave the best results, as far as Qvevri comparatively appeared to be more sustainable with its minerals.

Sample № 28, analyze fragment piece of Qvevri made in ceramic way showed us that it was furnaced on 1250°C temperature, the crystal structure of clay minerals were changed and transformed in amorphic almost vitreous state, which was expected.

 On sample № 29, where piece of fragment analysis of consuming jar showed that it was furnaced on 600°-700°C temperature. Cumulated mineral substances hardly has changed structurally. It is less sustainable and more easily transformable into liquid form, beside that we concluded according to the researches that pottery fragments and Qvevris made by the same materials are furnaced almost on the same degree temperature. That reaffirmed rightfulness of our research.   What about different quarries and Qvevris made by masters they differed from each other by their physical and chemical qualities, which must be caused by different primary clay mineral constituency extracted from the different quarries, combining them with two components (limestone, clay or river sand), waiting to become naturaly dry for awhile until furnacing procedures and after that exposing it on extremely different temperature.

Migration of Mineral Elements from Qvevri to Wine

We know that the fixing of sensory feelings of mineral substances in wine caused great interest within thewine makers and wine consumers in this last period. It is more and more often used word “minerality” in organoleptic evaluation of wine what can be explained by the sensory  taste of minerals during the evaluation of sensory sensitivity by wine specialists.  They try to expose those minerals by applying different methods as well.  

Many scientist try to find connection between taste of wine and minerals in soil. Leading wine specialists are paying lots of attention in organoleptic evaluation to  the concept of sensory-feelings of minerals in wine. As it is known minerals in the wine are feeding elements in form of Ions, with their small concentration, which have no smell and relatively lacking taste.

Beside that many specialist think that mineral sensoria in wine could be linked to the underground layers of vineyard and its geologic mineral taste in soil. Kaolin ((Al2Si2O5(OH)4)) and Gypsum ((Al(OH)3)) are able to produce different tastes in wine, and affect during the organoleptic evaluation. According to the research it is known that various minerals can cause positive or negative influence on wine aromas on basis of gustatory senses. Also, it is exposed the mineral’s effect with apple acid, on wine acid and on titrate acidity, as well as connection to the free or full sulfur peroxide.

We know that Qvevri is made by mechanically processed clay minerals found in ground soil, furnaced on certain limited temperature and represented as a wine vessel. Since the mechanically processed sweet grapes are placed in Qvevri and winery material left in it during 5-6 months and while an alcoholic fermentation goes on at that period we see a bio-chemical transformations and wine creation. As far as it was said that the various mixture of mineral substances from soil could affect on current bio-chemical transformations and create specific gustatory properties in wine, the same way we can suppose that Qvevri could affect on wine with its minerals, extracting ions, influence on bio-chemical  process of wine and its organoleptic evaluation for mineral gustatory senses. Of course, the distinctiveness of Qvevri wine and influence of Qvevri on wine needs the scientific conclusions.

To study transferring of mineral substances from Qvevri to wine, we conducted the experiment. Experimental Qvevris were stationed in village Napareuli, Telavi municipality, in wine cellar of Twins wine House in Napareuli Ltd and Rkatsiteli breed grape was chosen from their vineyard for the experiment, which was processed with Kakhetian (without pedicel) traditional technology for making wine accordingly and was placed in the experimental Qvevri and in neutral control and supporting ware. After the end of alcoholic fermentation, the Qvevri were filled from supporting neutral ware (sample 21) with initial wine fraction. Samples were taken from sweet, young, 3 and 6 month aged wine. The mineral substances analysis was carried out on the taken samples. (the tables are presented in the main work of the thesis).   The following mineral elements were identified: K, Mg, Na, Ca, Fe, Cu, Zn, Pb, As, Cl. The results of the analysis showed that quantity of the mineral elements of young wine in all Qvevri and control ware is the same within the margin of error.  Lead, arsenic, aluminum and manganese is sweet and wine was 0,002 - 0.007 mg/l. Their decrease and increase is significantly low number (0.001 – 0.002 mg/l), which is in margin error of analysis, thus they are not discussed further.

After analysis it was discovered that volume of potassium in sweet was transferred from the solid parts of dregs. Then acid salts (tartaric acids potassium) were created and absorbed from the 3 months old wine. During alcoholic fermentation, part of potassium was used by yeast for building its cells. And the part was adsorpted on yeast and solid parts of dregs.

All the mentioned and other processes caused reduction of potassium in young and 3 month old wine dregs. While in 6 months old wine, potassium is still increasing.

Changes of K, Mg, Na, Ca mineral elements in sweet, young wine, in 3 and 6 months old wines is given in the same tables as for potassium (the results are presented in the tables in main work of the thesis).

In some 3 and 6 months old Qvevri wines increase of these elements compared to neutral ware is being observed.

After comparing the results of Qvevri wine analysis with non-clay sample vessels, the comparison revealed that inconstancy of mineral elements from different Qvevri is unequal. Moreover, a sharp increase of mineral elements was observed in case of a few Qvevri, which proves the migration of mineral elements from clay-vessel. In addition, the results revealed, that in case of same wine liquid in different Qvevri, inconstancy of mineral elements between walls and liquid is unequal duet non-homogeneity of the clay-vessels.

Thus, studies have shown that the wine with 3 and 6 month delay, made from the grapes obtained from the same vineyard with the same technology, in the same conditions and kept in the Qvevri produced from the clays procured from the various fields and burned at different temperatures, considerably differs in mineral elements in comparison with the neutral (non-clay) vessels.

The experiment was repeated in 2017-2018 in the the same experimental Qvevri and ware in the same wine cellar, on the sweet and wine samples from the grapes taken from the same vineyard. Based on the results of analysis of both years, we can state that changing dynamics of mineral elements (in Qvevri and control ware) is almost the same, with insignificant differences.

Similar researches were conducted for the first and second factions of the wines delayed on dregs for 3 and 6 months. In the II fraction  of Kakhetian wine the number of mineral elements increased in comparison with I fraction, due to long delay on dregs and transition of mineral elements from the  dissolution products of yeast cells; The increase of mineral elements in  the I fraction of Kakhetian wine should be the result  of  wine interaction with Qvevri walls.

We also conducted studies on fragments of clays and Qvevri cylindrical cuts burned at different temperatures presented by us (samples N 4, 9, 14, 19, 23, 24, 25, 26, 27, 28, 29). In particular, they were placed and delayed in   water and in the fresh wine taken from the neutral vessel, as well as in the wines with different titrated acids. Conducted analyzes gave us the same results as  in the case of wines placed in different Qvevri, which once more    proves the interaction of mineral elements between the liquid  and the burned clay. (Tables are presented in the main dissertation work).

As we can see, the inconstancy of mineral elements in different Qvevri is unequal in comparison with the sample of neutral vessels, which, along with other factors, should be mainly determined by the heterogeneity of the Qvevri walls furnaced at different temperature.

Organoleptic Assessment of Wine

Conclusions made from the observation of  two years research results and the fact that that there was musty smell, specific taste, also brown color in some of Qvevri wines, made us think that it might be caused not by microbiological diseases (there was no sugar, titrical acidity and chlorinating was within norm) but by the influence of Qvevri.

We prepared two wine samples for degustation:

1.  Young wine material taken by us from the control neutral ware, in Autumn 2017 (before sealing of Qvevri and wares), which was poured in 5 L non-Qvevri neutral ware with furnaced clay-mineral fragments within it taken from the different mines (our research samples N 4, 9, 14, 19, 27, 28. Please see previous chapter). Whole area of wine contact with Qvevri walls and proportional equality contact of clay furnaced fragments’ area with the liquid in the wine were considered. We called these samples furnaced clay fragments in wine.

2. At the end of February 2018, we took 6 months old wine samples of primary fraction from all experimental Qvevri,  neutral non-Qvevri ware, Vardisubani Qvevri made in 1980 and metal ware.  We called this Qvevri and non-Qvevri wine samples.

Degustation was carried out on 1st of March, 2018, by the organisation of LEPL National Wine Agency under the Ministry of Agriculture, wine specialists and certified members of the Wine State Degustation Commission took part in it (please see degustation report).

The samples were assessed with 5 point rating system. Wine transparency and color intensivity were visually examined, and microbiological conditions, primary aromas, mineral and metal tones, taste senses of tannin, wet clay and saltiness were examined with taste-sensory assessment. Water solution sample was specifically made from raw clay, which was tasted before degustation, so wine tasters define clay taste and mineral tones. After that, first of all, wine tasters taste furnaced clay wine samples, than Qvevri and non-Qvevri made wine samples (assessments are described in the attached tables of the main part of the dissertation).

In some Qvevri wine is fixed a higher Qvevri taste sense, increased “wet clay” taste, saltiness and mineral tones compared to other wine samples. In our opinion, detection of “wet clay” taste and mineral tones was caused because of transferring some of the minerals or separate elements from the walls of Qvevri to wine. Saltiness taste might be caused by mixture of diffusion minerals (K, Na, Ca, Mg) of Qvevri walls with acids in the wine and formation of salts. These results are confirmed (furnaced clay fragments in wine) by the results of the first degustation, here again, higher Qvevri taste was detected in the wine samples. For example, according to the Table 1 (fragments in wine), Qvevri taste influence is mostly felt in the sample of Tkemlovana mine (Table 2). Similarly, Table 2 shows that wine tasters detected highest volumes of tannin and saltiness in the wine made in Tkemlovana Qvevri (Table 5). Similar results  are fixed in  Qvevri of Vardisubani (other results are in main part of the dissertation).  

To define physic-chemical characteristics, mineral compositions and furnacing temperatures, we know from the results of our research that Vardisubani and Tkemlovana Qvevri were furnaced on significantly lower 750°-800°C temperatures. It is also important that influence of Qvevri taste has not been detected in neutral, non-Qvevri ware wine and ceramic furnaced Qvevri fragment wine, which, according to our research was furnaced on 1200°-1250°C. The taste of Qvevri was slightly felt in Vardisubani (Qvevri made in 1980), Makatubani and Atsani Qvevri wines, were furnacing temperature, according to our research, is 950°-1050°C. This taste did not shade theprimarybreedaromas enriching the wine with unique freshness.

According to our research, the temperature of Qvevri furnacing, dynamics of the changing of mineral elements in Qvevri compared to the neutral ware, also the increased light “Qvevri clay taste” which fixed in organoleptic assessment and non-existence of this taste in some examples are in conjunction with each other.

Disscussion of the Experiment

To identify the meaning and identity of Qvevri and its influence on wine, we conducted following studies in 2016, 2017, 2018:

The petrographic (to define mineral composition and fractional granulometric sizes), X-ray phases (to define the quantity and essence of the predominant mineral elements) and  X-ray fluorescence (to define chemical composition and quantity of the elements) analyses were conducted on cylindrical cuts of Qvevri made from clay-minerals of different mines of Georgia and furnaced clay fragments.

At the same time, physic-chemical analysis was made on young wine material, 3 and 6 months old wines made in experimental Qvevri and neutral non-Qvevri ware and quantity of mineral elements was defined on each stage, which was compared with each other according to the periods and Qvevri, and quantity of mineral elements initially detected in sweet.

 By the organisation of LEPL National Wine Agency under the Ministry of Agriculture, wine specialists and certified members of the Wine State Degustation Commission carried out organoleptic assessment of our research wines regarding detection of Qvevri taste (minerals, tannin and saltiness tones).

Composition and furnacing temperatures of primary raw material from mines, clay-minerals for making Qvevri and mineral composition of Qvevri are different, there are different biological and physic-chemical processes in Qvevri while making wine; despite the fact that there is no microbiological diseases in wines, they are distinguished with light and high, sometimes pungent Qvevri (we can call it “wet  clay”) taste sensory tones while organoleptic assessment.

From all of this, we can conclude that mineral composition of Qvevri making material, technological process of making Qvevri, mainly, furnacing temperature, the combination of mineral elements in the sweet of grapes, technological process of making wine causes migration of different quantity of mineral substances from the walls of Qvevri to wine, which is reflected in the organoleptic assessment.  So, well-made Qvevri (solid and plastic clay-minerals selected specifically and with proper proportions, period of minimal natural drying, furnacing period and sintering maximum temperature 950°-1050°C) has positive influence on wine.

Economical Effect of Making Wine in Qvevri

Nowadays, high importance is given to the high quality wine made in Qvevri, and the market price of one bottle (0,750 ml), mainly, in selling points is 20-50 Gel. The selling price of the producer to the selling point varies between 10-15 Gel, while prime cost of one bottle (0,750 ml) of wine is 4,65 Gel, which gives an economic effect for production.

The demand for the Qvevri wine with hightasty qualities has increased along with its realization.

The Qvevri made from the proper technological instruction will no longer need to be waxed from  inside and cemented from outside (without cementing , it will be possible to transport the Qvevri  without damaging it) that will reduce the prime cost of the Qvevri by 15-20% and save the entrepreneur’s work time.

Conclusions

Multilateral experimental research confirmed that clay-minerals of different mines (Atsana, Satsable, Vardisubani, Tkemlovana) mines, with its mineral compositions, meets conditions of making material of Qvevri. Also, solid and plastic clay-minerals should be chosen with proper proportions. Mineral substances migration from the walls of the Qvevri, made from the different clay-minerals, furnaced on different temperature, happens in different dynamics, which might have positive or negative effect on wine quality.

According to physic-chemical analysis and degustation data, with violating technological process of Qvevri (furnacing on low temperature), quantity of the mineral substances in wine, taste of “wet clay” and saltiness tones increases, that influences organoleptic characteristics of wine and worsens its quality, which directly affect wine sales.

It was revealed that Qvevri, furnaced on 950°C-1050°C, is the best for making Kakhetian wine. It is recommended to the Wine Agency to develop standard for making Qvevri. Qvevri, made from this technology, gives an opportunity to get wine with high organoleptic characteristics.

Wine made in such a Qvevri is the best in terms of physical and chemical characteristics and has a pleasant, individual taste, which is positively reflected on realizationof the Qvevri wine and its consumers.

Therefore, the production of the best Qvevri and the Qvevri wine, along with other factors, depends mainly on:

- Mineral composition of primary raw materials.

-The quantity (percentage) composition of hard and plastic clay-minerals in building material of Qvevri.

- Furnace temperature.

Recommendation

Recommendation is given to the Ministry of Agriculture:

          -To conduct the field study of the mineral composition of raw materials used in production of the Qvevri.

-The complete technological instruction for Qvevri production (starting with the selection of primary raw materials, including the shape of the Qvevri and the burning  temperature) should be developed.

   -It is important to approve the standard for Qvevri, according to mineral composition of raw material, Qvevri makingprocess, shape, wall thickness, its porosity and burning temperature.

 -The Qvevri  masters' work should be  licensed.

        -It is important to approve the standard for Qvevri wine, according to organoleptic characteristics and physical-chemical data.

       -This will enable us to produce the quality Qvevri and make the best, unique taste and competitive Qvevri wine.

Tasting Protocol

LEPL National Wine Agency of Ministry of Agriculture of Georgia has organized a tasting of wine samples for research work submitted by Telavi State University postgraduate students Gia and Gela Gamtkitsulashvilis. Objective of the tasting was to explore influence that origins of Qvevri raw materials and Qvevri production technology makes on wine sensor properties.

At the testing, standard samples of sensor markers were introduced for calibration. For the purpose of definition of reliability of tasting, a triangle test was held. After calibration of research samples, namely,  6 model solutions and research samples of wine fermented in Qvevri 14 were appraised.

The research work authors Gia and Gela Gamtkitsulashvilis, the National Wine Agency chairman Giorgi Samanishvli, David Maghradze, head of  Viticulture Regulation Management of National Wine Agency and certified members of the Wine State Tasting Commission Irakli Cholobargia, David Chichua and Iago Bitarishvili have taken part in the tasting. The meeting was chaired by Ana Godabrelidze, head of the State Tasting Commission. David Chichua head of viticulture-winemaking service of the Research Centre, has acted as the meeting secretary.

List of works published around the dissertation

1.Gamtkitsulashvili Gia V., Gamtkitsulashvili Gela V. Producing Qvevri in present time and its influence on wine.// 4th International Qvevri Wine Symposium 2017. Ikalto Academy, Poster Presentation, September 1-3, 2017.

2.Gamtkitsulashvili Gia V., Gamtkitsulashvili Gela V., Khositashvili M. Influence of Qvevri on Wine.//Georgian Academy of Agricultural Sciences; International Scientific Conference “Viticulture and Wine-Making in European Countries – Historical Aspects and Prospects.” Poster Presentation October 25-27, 2017, Tbilisi.

3.Gamtkitsulashvili Gia V., Gamtkitsulashvili Gela V., Khositashvili M.L. Influence of Qvevri on Wine.//Georgian Academy of Agricultural Sciences; “Viticulture and Wine-Making in European Countries – Historical Aspects and Prospects.” October 2017, Tbilisi.

4.Gamtkitsulashvili Gia V., Gamtkitsulashvili Gela V., Khositashvili M.L. and Mikiashvili M.A. Dynamics of Changes in the Composition of Mineral Substances in the Must and Wine.// Georgian Engineering News №4, 2017.

5.Gamtkitsulashvili Gia V., Gamtkitsulashvili Gela V., Poporadze N., Metreveli R. Laboratory Research of the Material Composing Modern Wine Pitchers-Qvevri.//Georgian Social Academy of Young Scientists, International Scientific Journal “Intellectual” №35, 2018.

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