Twins Wine House

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

LEPL Iakob Gogebashvili Telavi State University

With the right to publish the manuscript

Gia Gamtkitsulashvili

Investigation of the clay minerals of the Kvevri and their impact on the quality of the wine

A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Food Technology

Abstract

Telavi

2018

The manuscript is developed at the Department of Chemistry and Agriculture of Iakob Gogebashvili Telavi State University

Academic Advisor: Mariam Khositashvili

Evaluators (reviewers): Tamaz Kobaidze

Guram Papunidze

The defense of the thesis will take place on December 11, 2018, at 12:00 at the Dissertation Board meeting of the Faculty of Agrarian Science of Iakob Gogebashvili Telavi State University: Building ---; Auditorium ----

Address: 1 Georgian University Street, Telavi, 2200, Georgia

Tel: +995 250 27 24 01

The dissertation can be obtained at the library of Telavi State University. It can also be retrieved from the following website: http://tesau.edu.ge

Academic secretary of the Dissertation Board: M. Kevlishvili

Overview of the Manuscript

Relevance of the topic. Georgian state has recently paid particular attention to viticulture and winemaking development. The restoration of state independence since the 1990s and the introduction of private property have allowed private owners and companies to introduce new technologies into production in winemaking. Under the competitive market conditions, the wine of Kvevri, an almost forgotten product, has started to re-emerge and re-establish itself slowly.

Many important historical sources and archeological artifacts indicate that Georgia is the homeland of wine. 80-century Kvevri-shaped vessel made from clay discovered in the village of Shulaveri is one of the numerous artifacts evidencing a long history of winemaking in Georgia. The scientists proved that ancient people used to make wine in this vessel as it contained grape seeds and wine fragments on the clay's wall. Since those ancient times, Georgian farmers have not ceased their relationship with vineyards and wine. They have also fully maintained the historical tradition of winemaking in Kvevri. Therefore, UNESCO recognized the Georgian winemaking technology as unique and included it in the world's intangible cultural heritage list.

The process of making Kakhetian wine differs from that of making European wines. The winemaking technology in Kakheti envisages alcoholic fermentation of sweets in a Kvevri on dregs (with or without stalk) and having it in hermetically sealed conditions for 5-6 months. It is known that the quantitative composition of minerals accumulated in the sweetness of grapes is directly related to the supply of minerals in the soil. After the mechanical processing of grapes, dregs are enriched with minerals. Therefore, they actively participate in the process of alcoholic fermentation and aging of sweet wines and microbiological and physicochemical conversion. This results in high content of extracts and tannins in it, ensuring relatively low acidity and a light body of Kakhetian wine. Such wine is rich in minerals, has healing properties, and has a positive effect on consumers' health.

Organoleptically, Kakhetian wine is significantly different, and winemaking specialists highly evaluate it. The composition of minerals in wine is influenced by the vessel itself. The mineral elements of the vessel actively migrate into the liquid. The presence of mineral elements and their amount in wine is quite significant. It can depend on the composition of the soil, their concentration in the sweet and the dregs, and at the same time, on the minerals of the vessel in which the wine is made. That's why the unique Kakhetian vessel-Kvevri plays an essential role in winemaking. Kvevri is handcrafted by processing and burning the natural raw materials - clay minerals. Accordingly, it is very important to study the structure of primary raw materials, solid and plastic clay minerals extracted from different ores of Georgia, and to determine the number of elements in it. Also, it is important to determine the physicochemical characteristics of the walls of Kvevri manufactured using the different clay minerals and fired at different temperatures. The investigation of the influence of different types of Kvevri on the quality of wine made from the same grape became crucially urgent and important.

The aim and objectives of the research: The overarching purpose of the research was to comprehensively study clay minerals and materials used for manufacturing Kvevri in different regions of Georgia (Study of mineralogy, amount of elements, firing/burning temperature) as well research mineral elements, chemical compositions and degustation data of wine produced in Kvevri.

The specific objectives of the research were:

To study the mineral composition of Kvevri substance and,raw materials extracted from different ores used for Kvevri making,as well as determine firing/burning temperature used in the Kvevri manufacturing process;
To determine the number of mineral elements in sweets and wines made in different types of Kvevri during different periods of wine aging;
To study the migration process of minerals from the Kvevri walls into the wine and their impact on its quality.

The scientific novelty of the research: The mineral composition, physicochemical characteristics, and distinctive features of the primary clay minerals, as well as materials used for producing Kvevri extracted from different ores of Georgia and the mineral composition of terracotta clay, have never been studied before. This research fill this gap by studying all the above-mentioned previously under-researched topics. The study revealed:

Different Kvevris have at least partially different drying and firing/burning temperature points. They also differ in terms of mineral composition and manufacturing technology;
Kvevri influences the mineral composition of wine and the variation of mineral elements of it. Kvevri also affects the organoleptic characteristics and quality of wine;
The study obtained the degustation data of organoleptic evaluation. It also analyzed physical and chemical compositions of the wines produced in Kvevri fired/burned at temperatures below -750-850˚C. The data revealed: (a) a sharp increase in the number of minerals in wines produced in this Kvevri; (b) The taste of "wet clay" and saltness in these wines. This, in turn, affected the organoleptic parameters of the wine and led to a deterioration of the quality of the wine.

The practical significance of the research: Studies have shown that to make a high-quality Kvevri, the mineral composition of the raw material extracted from the ore and the materials used for manufacturing the Kvevri must be studied; The threshold firing/burning temperature should be 950-1050˚C. Technological and methodological instructions and standards for Kvevri manufacturing should be developed; Kvevris made with this technology will allow us to get high-quality and competitive wines of Kvevris with different tastes and high organoleptic properties.

Economic effect. The dissertation experiment revealed that the quality of the wine placed in the Kvevri is influenced by many factors, including the quality of Kvevri. This finding underlined the importance of the proper selection of Kvevri manufacturing materials, complete management of technological processes of drying and manufacturing the Kvevri, and maintaining the optimum firing/burning temperature. The technologically improper manufacturing of Kvevri (production at a temperature below 800-850 C) has resulted in the deterioration of the quality of wine, accompanied by microbiological diseases, and an increased taste of Kvevri. The loss of quality and having the specific Kvevri taste decreased the satisfaction of wine customers. The decrease in satisfaction resulted in reduced sales of Kvevri wines. If the quality of Kvevri wines is maintained, the realization of the product will be stabilized. The market price of high-quality Kvevri wine ranges from 20 to 30 GEL. The on-site sale market price by the entrepreneur for the is between 10 and 14 GEL. The cost of one bottle (0.750 ml) of wine is 4.65 GEL. Accordingly, the economic effect of high-quality, well-produced Kvevri wine is well substantiated.

Reliability of Research Results. Several important factors ensure reliability of our study: (a) Samples of primary clay minerals were extracted by us together with the handcrafters of Kvevri; (b) Studies have been conducted on the latest high-sensitivity equipment using modern methods. The Central Tasting Commission of Georgia was involved in the process and participated in tasting samples of wines under the auspices of the National Wine Agency (see attached protocol).

Approbation: The results and activities of scientific research were discussed annually (2014-2018) at the Academic Board meetings of the Faculty of Agrarian Sciences of Telavi State University.

Publication. Three scientific articles were published on the research results conducted in the dissertation project framework. The findings were presented at two international conferences.

The structure and volume of the dissertation: The dissertation consists of the following parts: An overall description of the research, literature review, experimental part of the study, conclusions, and appendices. The thesis has 132 pages, 25 tables, and 17 photos. One hundred eleven references were used in the dissertation.

Experimental Part

Methods and objects of the research

To ensure that Kvevris in our study were identical to those presently manufactured in Georgia, we selected the best handcrafters of Kvevri Together with these masters, the primary raw materials were extracted from the ores, and the refinement and burning of clays were done in line with the technological procedures used by Kvevri manufacturers today. A total of 10 Kvevris were made from clay minerals extracted from the deposits of Makatubani (Satsable), Shrosha (Satsable), Atsani, Tkemlovana, and Vardisubani. The Kvevris were placed in September 2016 in the village of Napareuli in a specially built cellar of the company "Twins Wine House Napareuli". This study presents the findings of the samples of four Kvevris onlyWe obtained the following samples for the research:

Makatubani (Satsable/for Chestnut): №1-plastic material (akalo[1]); №2-non-plastic material (Tiri); №3 - mixed clay material; №4 - a piece of terracotta clay together with Kvevri. ; № 5 - Makatubani terracotta Kvevri Atsana: №6 - plastic material akalo); №7 – Sand of the river Rioni; № 8 - mixed clay material; № 9 - terracotta clay together with Kvevri № 10 - Atsani terracotta Kvevri; Tkemlovana: №11- plastic material (akalo); №12 - non-plastic material (Tiri); № 13 - mixed clay material; № 14 - terracotta clay together with Kvevri; №15 - Tkemlovana terracotta Krevri;

Makatubani (Satsable/for Chestnut): №1-plastic material (akalo); №2-non-plastic material (Tiri); №3 - mixed clay material; №4 - a piece of terracotta clay together with Kvevri. ; № 5 - Makatubani terracotta Kvevri Atsana: №6 - plastic material (akalo); №7 – Sand of the river Rioni; № 8 - mixed clay material; № 9 - terracotta clay together with Kvevri № 10 - Atsani terracotta Kvevri; Tkemlovana: №11- - plastic material (akalo); №12 - non-plastic material (Tiri[2]); № 13 - mixed clay material; № 14 - terracotta clay together with Kvevri; №15 - Tkemlovana terracotta Krevri;

Vardisubani #16- №1-plastic material (akalo); №17 – Sand of the river Rioni; #18 Mixed clay material; #19 a piece of terracotta clay together with Kvevri; #20 Terracotta Kvevro of Vardisubani.

The samples of clay material were counted at the sites, packed in specially prepared packages, and sent to the Research Laboratory of the Department of Applied Geology of the Georgian Technical University. A month later, terracotta clay materials, along with Kvevri, were sent to the same lab with relevant numbering.

A cylindrical-shaped neutral vessel of the same capacity (Non-Kvevri), called a neutral control vessel, was placed in the ground with several Kvevris in the cellar where the study was conducted. Another neutral control (non-Kvevri) vessel, called an auxiliary neutral vessel, was placed above the ground. After the alcoholic fermentation, the wine liquid decreased in Kvevri and in the control neutral vessel, and they were filled from an auxiliary neutral vessel located above the ground.

These vessels were given the following numbers: #21Neutral Control Vessel; #22 Auxiliary Neutral Vessel. Accordingly, we included six vessels in our research studies, four Kvevris and two neutral vessels. In addition, we made mechanical cylindrical cuts from the walls of our Kvevris (5,10,15, 20) and from the Kvevri made in Vardisubani in 1980. Cylindrical cuts were given the following numbering: №23 Makatubani Kvevri cylindrical cut; 24. Atsani Kvevri cylindrical cut; #25 Tkemlovana Kvevri cylindrical cut; #26 Vardisubani Kvevri cylindrical cut; #27 Vardisubani Kvevri of 1980 cylindrical cut.

For the purpose of our study, in the same period, we handcrafted another Kvevri and included it in the research. This Kvevri was made using a different technological procedure. Specifically, this Kvevri was manufactured with the technology used to produce high-strength ceramic pottery. It was fired in a closed electric oven for 24 hours at a temperature of 1200-1250˚C.

We also manufactured a clay jug fired at a low temperature for our study. We took the samples in the form of broken fragments from these two study objects. Accordingly, we obtained two more research objects with the following numbering: #28. Fragment of Ceramic Kvevri; #29. Fragment of the Jug.

Rkatsiteli grapes harvested in the company "Twins Wine House" vineyard located in Kakheti, Napareuli microzone in the village of Napareuli, were taken as a test object. We prepared the wine used for research with a single alcoholic fermentation of sweet and dregs without stalks. The wine had a 6-month delay on dregs. We removed the stalks from the grapes as it is known from the scientific literature that the stalks of a bunch of grapes contain the largest amount of minerals and significantly affect the migration of minerals into the wine. This could be an intervening factor and might cause problems with the validity of the study. The aim of the study was to determine the impact of Kvevri minerals on wine, and the minerals in the composition of stalks can play a negative role in the accuracy of the results of our study. Initially, grapes were nurtured in a drum mill, during which the stalks were removed from grapes. Dregs and the sweet of grapes were placed into the Kvevris and neutral control vessel. A sample of the sweet was taken during the grape processing period. Alcoholic fermentation proceeded steadily on natural yeast and lasted for 12 days, which is typical for Kvevri wine. When the alcoholic fermentation in the Kvevris and neutral control vessel had ended, new wine samples were taken. The Kvevris and neutral control vessel wines were kept for seven days. The sampled Kvevris for the study, as well as neutral control vessels were closed but unsealed. The amount of liquid decreased during these twelve days in Kvevris as well as in a neutral control vessel. We poured wine in Kvevris and in a neutral control vessel from an auxiliary control vessel located above the ground.

Wine samples were taken from Kvevris as well as from neutral control vessels three and six months after their sealing. Accordingly, we obtained the following research samples:

Sample - Control Sweet;

Makatubani N 5. Kv: Sample 1. – New wine; Sample 2. – Three months old wine; Sample 3. – Six months old wine. Atsani N10 Kv: Sample 4. – New wine; Sample 5. - Three months old wine; Sample 6. – Six months old wine.Tkemlovana N15 Kv: Sample 7. New wine; Sample 8. – Three months old wine; Sample 9. – Six months old wine.

Vardisubani N 20 Kv: Sample 10. - New wine; Sample 11. – Three months old wine; Sample 12. – Six months old wine; Neutral Control Vessel N 21: Sample 13. - New wine; Sample 14. – Three months old wine; Sample 15. – Six months old wine; Auxiliary Neutral Vessel N 22: Sample 16. – New wine;

Samples were bottled, sealed, numbered, and sent to the Wine Laboratory (Wine Laboratory Ltd.). The studies continued to be conducted in 2017 as well.

We studied the raw materials which are extracted from ores (solid and plastic clays), Kvevri wall clay materials, terracotta clay materials, Kvevris cylindrical cuts, ceramic fragments of ceramic Kvevri, and the fragment of ceramic jug at the laboratory of the Department of Applied Geology of the Technical University of Georgia. The investigation aimed to determine the physical and chemical characteristics and mineralogical composition of these materials.

The samples were studied through:

Petrographic analysis using a polarizing microscope (AMSCOP 600T) to determine their structure, mineralogical composition, and fractional granulometric dimensions.
X-ray analysis (DRON-3) determined the number of predominant mineral phases and firing/burning temperature.
X-ray fluorescent analysis using a spectrometer - EDX3600B, which determined the chemical composition and content of the elements.

The basic parameters of the quality index were determined for the controlled sweet and sampled wines using the methods of sweet and wine analysis identified in the scientific literature and prescribed in the international standards of the International Wine Organization.

Plasma-emission spectrometer was used to determine the number/quantity of minerals in the samples of controlled sweets and sampled wines. The method of measuring metals with this spectrometer is based on the measurement of the spectral wave intensity of those elements when inflamed in the instrument through the introduction of sample elements (in the form of an aerosol) at which the intensity is perceived on the detector. The relationship between the radiation intensity of the elements and their concentrations is established by building calibration graphs. The method ensures that the measurement results are recorded within the minimum error.

Preparation of samples for micronutrient analysis involves preparing standard and caliber solutions. Analytical wavelengths that are different for all elements must be pre-selected to measure the sample. Before working on the spectrometer, we checked the pressure, turned on the plasma, and entered the samples into the spray system; The samples scattered and hit the plasma. Concentrations obtained after measurement are expressed in mg / l.

The research of physical and chemical characteristics and mineralogy of Kvevris and raw materials used in manufacturing of Kvevri

The selection of ores for the extraction of raw materials, its refinement, the handcrafting of the Kvevri, and the firing/burning temperature have particular importance. The fractional-granulometric size and dimensions of the minerals contained in the first raw material extracted from the ore are of great importancsignificance foranufacturing.

Clay minerals are characterized by high, medium, and low plasticity. The higher the number of pure particles of clay minerals in the raw material, the more plastic is the material. In addition, great importance is attached to the technological mode of manufacturing Kvevri - drying of the Kvevri and its firing/burning. Due to the unique taste properties of Kvevri's wine, wine experts have suggested that the Kvevri should impact the quality of the wine and that Kvevri is not a neutral vessel.

Accordingly, our research set the next objective to study physical and chemical characteristics, mineralogy of samples obtained by us (primary raw materials of clay minerals, materials used for the production of Kvevri, fragments of terracotta clay with Kvevri, cylindrical cuts, ceramic Kvevris, and jug). The investigation of proper firing/burning temperature for Kvevri was also one of the interests of our research study. Samples taken by us ranged from 1 to 27, and petrographic, X-ray, and X-ray fluorescent studies were conducted for the samples.

The results of the analysis revealed that the mineral composition and the number of elements depicted in raw materials were almost preserved in the samples obtained after the firing/burning (see Tables); this fact indicates that mechanical processing and subsequent firing/burning could not change the composition of minerals and number of elements. Accordingly, we present here only the following samples:

№4 – Makatubani (Satsable) – The terracotta fragment of clay made from Akalo (type of clay) and Tiri (type of clay) taken from the ore of Makatubani;

№ 9 - Atsana- The terracotta fragment of clay made from Akalo (type of clay) and Tiri (tyoe of clay) taken from the ore of Atsana;

№ 14 Tkemlovana- - The terracotta fragment of clay made from Akalo (type of clay) and Tiri (type of clay) taken from the ore of Tkemlovana;

№ 19 -Vardisubami- The terracotta fragment of clay made from Tiri (type of clay) and sand of the river Alazani.

№ 23 Makatubani cylindric cut of Kvevri

№ 24 Atsana ა cylindric cut of Kvevri

№ 25 Tkemolavan cylindric cut of Kvevri .

№ 26 Vardisubani cylindric cut of Kvevri.

№ 27 Vardisubani cylindric cut of Kvevri (1980)

№ 28 – Frangment of Ceramic Kvevri.

№ 29- Fragment of customer jug.

The detailed information about microscopic research of these samples, including photos and charts, can be seen in the dissertation.

We included sample #4 for illustration of the results in this abstract. Sample #4 Makatubani (Satsable) is the terracotta fragment of clay made from Akalo (type of clay) and Tiri (type of clay) taken from ore of Makatubani. The Sample is a macroscopically reddish fragment of color, inclusions of various sizes and colors are observed on the surface of the piece. It does not react with hydrochloric acid. It is porous when observed with a loop, although it does not actively absorb water.

Under the microscope, the binder, or core mass, is represented by an amorphous clay mass; the filler, i.e., fragments of rock and individual minerals, are numerous and of different sizes, and individual minerals with different sizes and shapes are dominating. Fragments of rock are also rare. Plagioclase predominates in the mineral composition, which is always replaced by secondary minerals (clay minerals, sericite); amphibole grains are rarely found.

The rock fragments are relatively small and are mainly represented by quartz-meadow fine-grained rock fragments. In many cases, the pieces are replaced, and only their forms are maintained.

X-ray analysis of a sample Makatubani (Satsable) - the terracotta fragment of clay made from Akalo (type of clay) and Tiri (type of clay) shows the following phases: Quartz 7-10%; Ca-Na field slopes 20-25%; Amphiboals are at the level of traces. The rest of the dispersive X-ray amorphous phase. The Kvevri is probably fired at 950 -1000˚C degrees.

The research results revealed that the rock-forming/clast and chemical contaminant elements in the raw materials extracted from Vardisubani, Tkemlovani, Makatubani, Atsana deposits differ.

The quality of the Kvevri depends on the composition of the primary raw material - clay minerals, on the quality of its refinement, and on the drying and firing/burning process. Mechanical minerals in the raw material used to make the Kvevri: quartz, feldspars (plagioclase, K feldspar), pyroxenes, and amphiboles – are resistant to the firing/burning process until the 950-1000 ° C; however, they still undergo some structural changes. After firing/burning, the walls of the Kvevri became partially retained by pores. Their quantity and sizes mainly depend on: (a) the quality of the plastic minerals that make up the raw material; (b) granulometric size; and (c) the firing/burning temperature. The relatively large size of the pores allows harmful microbes to be trapped in the empty Kvevri. This process is undesirable for wine production. The studies revealed that Kvevris made from different ore differ in mineral composition and manufacturing technology, especially in firing/burning temperatures (our study showed that firing/burning temperatures range from 750 ° C to 1050 ° C). Studies have shown that firing/burning a Kvevri at a temperature of 950 ° C - 1000 ° C gives the best results because, at this temperature, the Kvevri contains relatively stable minerals.

Sample N28. Analysis of a fragment of a ceramic Kvevri showed that when it was fired at 1250 ° C, the crystalline mass of the minerals changed and became amorphous, almost glassy, which was to be expected.

The analysis of Sample N29. Fragment of consumer jug showed that it was burned at 600-700 ° C. The unity of the mineral substances has hardly undergone structural change. It was less durable and easily cracked.

Analysis of studies has shown that the firing temperatures of clay fragments and Kvevri made from the same raw material are almost the same.

Kvevris made by different handcrafters from different minerals extracted from different ores were found to be completely different in their physicochemical characteristics. This was due to the several reasons: (a) heterogeneity of the mineralogical composition of the primary minerals; (b) The mixing of the two components (Tiri, Akalo, or sand of the river) in different proportions by the masters; (c) differences in the period of delay of natural drying of the Kvevri and ; (d) the sharp difference in firing temperatures.

The migration of mineral elements from Kvevri to wine

It is known that winemakers and consumers have been particularly interested in the sensory taste of minerals in wine. The word "minerality" is increasingly used in the organoleptic evaluation of wine. Even though winemakers feel the taste of minerals in wine, they use different methods to present the minerals. Many scientists are attempting to connect the taste of wine with the minerals in the soil. The world's leading wine specialists pay special attention to the sensory of wine minerality concept during an organoleptic evaluation. It is known that the minerals in wine are nutrients in the form of ions. Their concentration is small, they have no aroma, and the taste is hardly detected. Nevertheless, many experts today believe that mineral sensibility in wine can be related to the taste of geological minerals found in vineyard rocks and soil. According to scientists, kaolinite (Al2Si2O5 (OH) 4) and gibbsite (Al (OH) 3) have the ability to form different flavors in wine and influence organoleptic evaluation. Studies have shown that different minerals have a positive or negative effect on the aromas of the wine. These differences are detected during taste sensation. The influence of mineralization on malic acid, tartaric acid, titratable acidity, and the connection of mineralization with free or complete sulfur peroxide has also been identified.

Kvevri is a wine vessel made from a material obtained from the mechanical refinement of clay minerals extracted from the ground and fired at a certain temperature. The sweet grapes are mechanically put in Kvevri, and the wine material obtained as a result of alcoholic fermentation stays in the Kvevri for 5-6 months. This is the period when biochemical transformations and wine formation take place intensively. It has been proved that different minerals from the soil could transform wine's biochemical composition and change its taste. This fact pushed us to the following assumption: Extracted minerals from the Kvevri migrated into the wine in the form of ions will also affect the wine's quality and mineral taste sensation during the organoleptic evaluation. It is evident that our assumption of the influence of Kvevri on the taste of wine requires scientific justifications.

We conducted an experiment to study the migration of minerals and individual elements from Kvevri into wine. Rkatsiteli grapes grown in the vineyard of Napareuli microzone were selected. The wine was made based on Kakhetian (taking stalk from grape) technology for making wine. The wine was placed in experimental Kvevris and in neutral control and auxiliary vessels. After the alcoholic fermentation, the Kvevris were filled from the auxiliary neutral vessel (sample 21) with the first fraction of wine. Samples were taken from both sweet and young wines aged three and six months. The analysis of mineral elements was conducted in the samples ( The tables depicting the results of the analysis are presented in the dissertation). The following elements were defined: K, Mg, Na, Ca, Fe, Cu, Zn, Pb, As, Cl. The analysis of the results showed that the number of elements in the composition of young wine in all Kvevris and neutral control vessels is almost identical within the margins of error. The lead, arsenic, aluminum, and manganese were found in sweets and wine at 0.002 - 0.007 mg / L. The fluctuation (decrease and/or increase) of these is very small (0.001 - 0.002 mg / l), which falls under the margins of error; accordingly, their results were not discussed.

After analysis, it was found that the amount of potassium in the wine in the neutral vessel shifted to sweet from the solid parts of the dregs. Acid salts (tartaric potassium) were then formed and precipitated in wine with delay for three months. During alcoholic fermentation, part of the potassium was used by yeast to build up its cells. Part of it was adsorbed on solid parts of yeast and dregs. All these and other processes have resulted in potassium depletion in new and in three-month-old wines made with dregs. In six-month-old wines, the amount of potassium was almost the same. The same changes in mineral elements such as Mg, Na, Ca were observed in sampled sweets and wines. (the results are given in the tables of the dissertation).

Contrary to the processes observed in the neutral control vessel, all above-mentioned mineral elements (Potassium, Mg, Na, Ca) increased in the three and six months old wines in sampled Kvevris. The comparison of sampled wines with controll neutral vessel wine revealed that mineral element fluctuation differs greatly. At the same time, the increase of mineral elements was observed in sampled Kvevri wines, which proves that mineral elements were migrated from Kvevri to liquid. The study also revealed that different type of Kvevri with the same kind of grape has a different type of migration of mineral elements from the walls of Kvevri to the liquid.

To sum up, our experiment proved that the same kind of grapes picked up from the same vineyards with the same technology, under the same conditions, differ in the composition of mineral elements depending on the vessel they are made. The three or six months old wines made in Kvevri, which was manufactured from clay minerals extracted from different ores and fired at a different temperature, has different mineral composition compared to wines produced in neutral (non-.clay) vessels.

The experiment was reiterated in 2017-2018. The same grapes of the same vineyards as well as the same sampled Kvevris and neutral control vessels were used in the recurrent experiment. The experiments of these years confirmed the findings of previous experiments. The dynamics of changes of mineral elements in different vessels (In Kvevris and neutral control vessel) were almost the same, with the differences within the margins of error.

The analogical research study was conducted on the first and second fractions of the wines produced with dregs of three and six months of preservation. The research revealed that mineral elements in the second fraction of Kakhetian wines increased more compared to the first fraction of the wines due to the time of preservation on dregs and the transfer of mineral elements from the fragmentation of yeast cells. The increase in mineral elements in the first fraction of Kakhetian wines should be caused by the interaction of Kvevri walls and wines.

The research was also conducted on clays fired at different temperatures and fragments of Kvevris cylindric cuts sampled for our studies (Sample N 4, 9, 14, 19, 23, 24, 25, 26, 27, 28, 29). Specifically, they were placed with delay in water, young wines, and wines of various titratable acidity taken from neutral vessels. The study data showed similar results depicted in the research of Kvevri wines. This data further confirmed the interaction and exchange of mineral elements between liquid and terracotta clay (Tables are presented in the dissertation).

As the study data revealed, the different Kvevri’s wines have a different variance of mineral elements compared to wines of neutral control vessels. This fact can be explained by the varieties of Kvevri’s walls fired at different temperatures, among other factors.

Organoleptic evaluation of wine

The findings of a two-year study, and the fact that some wines of Kvevri had the taste of clay and sour, suggest that they may have been caused not by microbiological diseases (never residual sugar, but normal by acidity, etc.) but by the influence of Kvevri.

We prepared two samples of wines for degustation:

In the fall of 2017 (before the Kvevris and vessels were sealed) we took young wine material from the control neutral vessel, which was poured into neutral vessels with a capacity of 5 liters, and fragments of burned materials taken from different ores ( Sample # N 4,9,14,19,27,28, see the previous chapter for details). The total area of wine contact with the walls of the Kvevri and the proportional equality of the area of contact of the terracotta clay fragments embedded in the wine with the liquid was taken into account here. This sample was named fragments of terracotta clay in wine.
We took the samples of six-month-old wine from all sampled Kvevris of our cellar, from the neutral control vessel, the Kvevri manufactured in Vardisubani in 1980, and the metal reservoir in February 2018. These samples were named the samples of Kvevris wines and samples of neutral vessel wine

The wine degustation took place on March 1, 2018, by LEFL Wine National Agency of the Ministry of Agriculture of Georgia. The specialists of wine as well as certified members of the wine tasting state commission participated in the degustation process (The protocol of degustation at attached).

Samples were evaluated on 5 point scale. Wine transparency and color intensity were conducted with visual assessment. Taste sensation assessment was used to assess microbiological status, primary aromas, mineral and metallic tones, and sensitivity to the taste of tannins, wet clay, and salt.

A sample of an aqueous solution was prepared from the raw clay and tasted before degustation. This approach enabled the wine-tasters to observe the taste and mineral tones of the clay. Then, in the first stage, samples of terracotta clay wine were tasted, followed by samples of wines made in Kvevris and in other vessels. (estimates are presented in the tables as appendices of the dissertation).

The average evaluation scores for both types of samples were calculated based on degustators evaluation. The data is presented in tables.

Table1. The average score of degustation evaluation of fragments of terracotta clays placed in wine

Sample#	Transparency	Intensity of color	Initial aromas	Microbilogical	Wet clay	Mineral	Tanini	Saltness	Metalic
1	3,75	2,25	2,00	0,63	0,13	1,63	3,28	4,13	0,25
2	3,75	2,13	2,50	0,75	0,5	2,38	4,38	3,63	0,25
3	3,25	2,75	1,75	1,25	0,50	1,25	4,00	2,25	0,38
4	3,50	2,50	2,38	1,00	0,13	1,88	3,75	2,63	0,25
5	3,63	2,75	2,50	0,75	0,13	1,88	3,63	2,50	0,13
6	3,38	2,63	2,13	1,00	0,38	2,13	3,63	2,63	0,38
Average	3,54	2,5	2,21	0,90	0,30	1,86	3,78	2,96	0,27

Table 2. The average score of degustation evaluation of sampled Kvevri wines

Sample#	Transparency	Intensity of color	Initial aromas	Microbilogical	Wet clay	Mineral	Tanini	Saltness	Metalic
1	3,38	1,63	2,75	1,88	0,38	1,13	2,75	2,13	0,13
2	3,50	3,13	2,38	1,63	1,00	2,13	3,50	2,63	0,13
3	3,50	3,13	2,63	1,88	1,50	1,88	3,38	2,50	0,13
4	2,63	2,63	2,38	1,13	0,50	1,63	3,00	2,13	0,00
5	3,13	2,63	1,75	1,88	2,25	2,75	2,63	2,25	0,00
6	2,38	2,00	0,50	3,25	0,88	1,50	2,00	2,13	0,00
7	3,50	3,13	2,38	2,00	0,75	1,88	3,13	1,88	0,13
8	3,75	2,38	3,25	1,25	0,25	1,50	2,50	1,63	0,25
9	3,00	3,25	2,25	2,75	1,00	2,13	2,88	2,13	0,13
10	3,50	3,25	2,40	0,88	0,63	1,50	2,88	2,25	0,13
11	3,50	3,25	2,38	1,63	1,00	2,38	3,38	2,25	0,25
12	3,00	2,88	2,38	1,00	0,63	1,63	2,75	1,63	0,38
13	3,13	2,63	2,25	1,00	0,75	1,13	2,75	1,88	0,25
14	3,50	2,75	2,63	0,88	0,25	1,38	3,00	1,75	0,13
15	3,50	2,13	1,88	1,00	0,63	1,50	2,75	2,13	0,38
Average	3,26	2,72	2,28	1,60	0,83	1,74	2,89	2,09	0,16

Cross-observations of the results given in both tables show that the influence of Kvevri’s flavor (Minerals, Tannins, Saltness) is high, medium, and low in the wines produced in the Kvevris from the same ore. Analysis of the evaluations of the observed results also shows that the changes in the organoleptic data of the same wine are caused precisely by the relationship of the walls of different Kvevris with the wine.

The wines of some Kvevris have high flavor sensitivity. The flavor of “wet clay” , saltness and tones of minerals are extensively presented. We argue that the taste of "wet clay" and mineral tones is due to the transfer of some minerals or individual elements from the walls of the Kvevri to the wine. Salt tones should be induced by the combination of diffuse elements (K, Na, Ca, Mg) from the Kvevri walls with the formation of salts with tartaric acids. These results are confirmed by the results of the first tasting (fragments of terracotta clay placed in the wine), where the increased tones of the Kvevri’s taste coincide with the tones of the similar Kvevri wine. Here is an example of one Sample: According to Table 1 (fragments in wine) most of the Kvevri flavor influence is felt on the Tkemlovana (Table N2) ore sample. Similarly, from Table 2, it can be seen that the sensitivity of wet clay and minerals by the tasters was mostly observed in the wine made in Tkemlovana (Table N5). Tannins and saltness were also high in this sample. Similar results are observed in the case of Vardisubani Kvevri (the rest of the data are presented in the dissertation).

The investigation of physical and chemical characteristics, mineral composition, and firing/burning temperatures of Kvevris revealed that Vardisubani and Tkemlovani Kvevris were fired at low temperatures of 750-800 C. Additionally, no flavor of Kvevri was observed in wines from the neutralcontroll vessel (non-clay vessel) and from the wines of fragments of terracotta Kvevri fired at the temperature of 1200-1250°C. The flavor of Kvevri was slightly observed in the samples of Vardisubani 1980, Makatubani, and Atsana Kvevris. These Kvevris are manufactured through firing/burning at the temperature of 950-1000 °C. This taste did not obscure the initial varietal aromas of wine and gave the wine a different velvety and cheerfulness.

The observation of the research results revealed that the results of the organoleptic evaluation of sampled wines are influenced by the temperature of firing the clay Kvevris and by the dynamics of fluctuation of mineral elements in wines of Kvevri. Specifically, the flavor of “wet clay”, saltness, and mineral tones in some samples of wines, light or no flavor in other samples of wines are the result of the influence of Kvevri, the temperature they are fired, and the dynamics of fluctuation of mineral elements in Kvevris.

Discussions

The following research studies were conducted in 2016, 2017, and 2018 to identify the mean and identity of Kvevri:

The raw materials are extracted from ores (solid and plastic clays), Kvevri wall clay materials, terracotta clay materials, Kvevris cylindrical cuts, and ceramic fragments of Kvevri, and the fragment of ceramic jug were studied through 1. Petrographic analysis to determine their structure, mineralogical composition, and fractional granulometric dimensions.2. X-ray analysis to determine the number of predominant mineral phases and firing/burning temperatures of Kvevris;3. X-ray fluorescent analysis to determine the chemical composition and content of the elements.

At the same time, the sampled new, three, and six-month-old wines of Kvevri and neutral control vessel wines were studied in terms of physical and chemical composition. The number of mineral elements in these sampled wines was measured at different stages of winemaking. The obtained data on mineral elements were compared to the initial data measured in grape sweets.

The degustation of wines was conducted by LEFL Wine National Agency of the Ministry of Agriculture of Georgia. The specialists of wine as well as certified members of wine degustation state commission participated in the degustation process. The organoleptic evaluation of our sampled wines was done during the degustation. The flavor of Kvevri wine (Minerality, tannins, and saltness tones) was tested.

The observation of the research results revealed that the raw materials extracted from ores (solid and plastic clays), the mineral composition of Kvevri, and the firing temperatures of clay differ. Different biological and physicochemical processes take place during the fermentation of the wine in Kvevris. Even though, microbiologically, the wines did not have diseases, they differed in the sensory tones of “wet clay” (high, medium and low sensitivity) during the organoleptic evaluation.

It can be concluded that the mineral composition of clay materials, Kvevri manufacturing technology (especially firing/burning temperatures, and the mineral elements of grape sweets are the factors having an influence on the migration of mineral elements from Kvevri walls into the liquid. This finding is also confirmed by organoleptic evaluation. Accordingly, the properly manufactured Kvevri ( proportionally selected solid and plastic clay materials, natural drying period, firing/burning temperature of 950 ° C - 1000 ° C) gives the best results and positively impacts wine.

Economic Effects of Kvevri Winemaking

The Kvevri wines, characterized by high quality, are popular today. The price of high-quality Kvevri wines in markets ranges from 20 to 30 GEL. The on-site sale price by the entrepreneur for the markets is from 10 to 14 GEL. The cost of one bottle (0.750 ml) of wine is 4.65 GEL. Accordingly, the economic effect of high-quality, well-produced Kvevri wine is evident. If the quality of Kvevri wines is maintained, the realization of the product will be increased.

Kvevri made according to the correct technological procedures will no longer need to be waxed from the inside and/or cemented from the outside (It will make possible the transportation of the vessel without damaging it), which will reduce the cost of the Kvevri by 15-20%, and save entrepreneur’s workload.

Conclusions

Multiple experimental studies revealed that some ores of clay raw materials in Georgia (Atsana, Satsable, Vardisubani, Tkemlovana) with their mineral composition makes it possible to manufacture the high-quality Kvevri for winemaking.

The study also revealed that Kvevri influences the mineral composition of wine and the variation of its mineral elements . Distinctive features of the primary clay minerals, the firing temperature of terracotta clays, and the dynamics of fluctuation of mineral elements in wines of Kvevri, influence the migration of mineral elements from Kvevri walls into the liquid.These processes positively or negatively impact the quality of the wine.

The study obtained the degustation data of organoleptic evaluation. It also analyzed the physical and chemical compositions of the wines produced in Kvevri fired at temperatures below -750-850˚C. The data revealed the sharp increase in the number of minerals in wines produced in this Kvevri and the increase in the flavor of "wet clay" and saltness in these wines. This, in turn, affected the organoleptic parameters of the wine and led to a deterioration of the quality of the wine, and had a negative impact on attracting customers to use wines of Kvevri.

Our studies have shown that to make a high-quality Kvevri, the threshold firing/burning temperature should be 950-1050˚C. Kvevri made with this technology will allow us to get high-quality and competitive wines of Kvevri with different tastes and high organoleptic properties. The wine made in this type of Kvevri has the best physicochemical characteristics and is distinguished by a velvety, different taste, which has a positive effect on the sale of wines of Kvevri.

Thus the production of the best wine, among other factors, mainly depends on:

On the mineral composition of primary raw materials.
Kvevri manufacturing materials, the quantitative (percentage) composition of solid and plastic clay minerals.
The firing temperature of clay.

Recommendations

Recommendations for the Ministry of Agriculture:

To study the mineral composition of the raw materials for making Kvevris from the ores of Georgia.
To develop a complete technological instruction for making Kvevri (starting with the selection of primary raw materials, ending with the shape of the Kvevri, and defining the firing temperature).
To develop a standard for manufacturing Kvevri based on the mineral composition of the raw material, the instruction for Kvevri making, the standards on shape and thickness of Kvevri, firing temperature, and
To introduce the licensing system for Kvevri handcrafters.
To develop Kvevri wine standard based on physicochemical data and organoleptic characteristics.

If the recommendations are implemented, it will be possible to handcraft the Kvevri with high quality and produce the best, most competitive wine of Kvevri with different flavors.

The list of publications based on dissertation data and materials

Gamtkitsulashvili Gia V., Gamtkitsulashvili Gela.V. Manufacturing of Kvevri in Georgia in the current period and its impact on wine. // 4th International Kvevri Wine Symposium. Ikalto Academy; Report September 2-3, 2017.]

Gamtkitsulashvili Gia V., Gamtkitsulashvili Gela.V, Khositashvili ML The Impact of Kvevri on Wine // Georgian Academy of Agricultural Sciences; International Scientific Conference "Viticulture and Enology in European Countries - Historical Aspects and Perspectives". Report October 25-27, 2017.

Gamtkitsulashvili Gia V., Gamtkitsulashvili Gela.V, Khositashvili ML The Impact of Kvevri on Wine // Georgian Academy of Agricultural Sciences; "Viticulture and winemaking in European countries - historical aspects and perspectives." Tbilisi, October, 2017.

Gamtkitsulashvili Gia V., Gamtkitsulashvili Gela.V, Khositashvili ML, Mikiashvili MA Dynamics of variability of mineral composition in sweet and wine.// Engineering News №4, 2017.

Gamtkitsulashvili Gia V., Gamtkitsulashvili Gela.V, Poporadze N., Metreveli R. Laboratory examination of the constituent material of modern Kvevris // International Scientific Journal of the Georgian Academy of Young Scientists "Intellectual" №35, 2018.

Appendix 1 Protoco of Degustation

LEPL Iakob Gogebashvili Telavi State University