Storing grapes in refrigerator
The current guide refers to Vitis vinifera fresh table grape and its storage indicating the rules of its storage in refrigerated storeroom with a capacity of 25-150 tonnes by fumigation with airing and sulphur dioxide.
Raw materials
- The clusters should match with primary commercial varieties of grape, the stalk of grape should be green and elastic, grape berries should be covered with wax and should be whitish green or golden brown in white grape varieties.
- The grape harvest is better stored once active temperatures total 3500-3600°.
- The grapes should be harvested in dry weather and the grape berries should not be wet during harvesting. Harvesting is not allowed in rainy and cloudy weather. Blunt scissors should not be used.
- The clusters should be examined and the damaged, withered and dry grape berries should be removed. One should hold on the stalk while removing unripe and rotten grape berries in order to protect the wax layer.
- 1-1, 1-2 boxes are used for harvesting.
Technological scheme
- The grapes should be very carefully packed into boxes for storage. The grapes should be packed tightly with the stalk of grapes standing upward. The upper row should be straight and not more than 2 cm-2.5 cm higher than the sides of the box. The weight of each box packed with grapes should not be more than 8.5 kg.
- The grapes should be stored in a refrigerator right on a day of harvesting.
- Once it takes long to fill up the refrigerated storerooms (up to 3-5 days), the harvested grapes should be cooled in advance in special storerooms at 8-10° for 10-12 hours. If to place uncooled grapes in refrigerated storerooms, the temperature of the storeroom will rise leading to an increased moisture content of the grapes stored earlier. It is not required to cool down grapes in case the refrigerated storerooms can be filled in a day. In this case, grape temperature is reduced up to 2°C and the grapes are stored in a storeroom directly from the field.
Requirements for storerooms
- Grapes are stored in refrigerated storerooms with a capacity of 25-150 tonnes and special ventilators are used to regulate the air inside the storeroom.
- Storerooms should be disinfected 10-15 days before the harvesting and the interior of the storeroom should be sprayed with 5% ferrous sulphide solution to kill mildew fungus. Then it should be whitened with new 20% lime solution. 0.3 litres of solution is used per m². Following the whitening, the storeroom is dried at ambient temperature and aired.
- 1-3 days before the storage of grapes, storerooms are fumigated with sulphur anhydride. For this purpose, sulphur anhydride is burned in an iron container. The anhydride is divided into smaller parts to let it burn better and then mixed with dry bran and ammonium saline. 50 gr of sulphur with a ratio of 70:8:22 is used per 1 m³. 100 gr of gas is used per 1m³ from a container filled with anhydride. The gas consumption is controlled by scales.
- Once the disinfection is over, the refrigerator is switched on and the storeroom temperature is reduced up to 2°C. All refrigeration batteries should be covered with polyethylene film (screen) before filling the storeroom. To ensure a free heat exchange, the top of the screen should be at the level of the upper battery pipe while the bottom of the screen should be 0.5-0.6 m from the floor. The distance between the screen and refrigerator should be 0,15-0,20 m.
Rules for filling up storerooms
- Each of the storerooms should be filled with grapes of the same ampelographic variety. Other ampelographic varieties with the same storage time can also be used to fill up the storeroom quickly.
- The boxes filled with grape are packed on the bottom in 10-12 rows. The pallets are placed on a stack in not less than two layers. The distance between the upper point of the stack and ceiling should not be less than 0.6 m. In case of absence of a refrigerator, the distance between the stack and the wall of the storeroom should not be less than 0.6 m while it should not be less than 0.8 m in case of presence of refrigerators.
- It should not take more than 3-5 days before a storeroom is completely filled up.
Storage mode and conditions
- The temperature and humidity in storeroom should be kept stabile while grape is being stored. The accepted temperature can vary between ± 0,5°C and air humidity can vary ±3%.
- Once storeroom is filled up, its temperature is reduced up to 0...+1°C within a day and kept stabile till the end of the storage period.
- The relative air humidity in the storeroom should be 90%-95%.
- The control points for measuring temperature and humidity in refrigerated storeroom should be distanced from each other and the number of those control points should not be less than three. One of them should be located in the hottest point, one – in the coolest point while the third one should be located in the middle of the central or side passage at a height of 1.5-1.6 m from the floor. The temperature and humidity in storeroom are defined as a mean value of air temperature and humidity in control points in each stage of measurement.
Note: the hottest and the coolest points of an empty storeroom should be indicated in the design documentation of storeroom.
- The storage conditions of grape shall be controlled not less than two times a day. In case of distant control equipment, it shall be done every two hours.
Once a storeroom is filled, it is fumigated with 6-10 grams of sulphuric liquid anhydride or by burning 3-5 grams of solid sulfur per m³. During the whole storage time, a fumigation is done every 7 days with 2-3 grams of sulphuric liquid anhydride and 1-1.5 grams of solid sulfur. The fumigation should be stopped at least 10 days before the end of the storage period.
Storage of grapes in controlled atmosphere
Controlled gas atmosphere or controlled atmosphere (controlled atmosphere CA) allows to store grapes without loss of nutritive qualities for 7-9 months. This method is about regulating the ratio of the main components of the atmosphere - nitrogen, carbon dioxide and oxygen. It is possible to obtain a special medium having a lower respiration rate, thus slowing down the process of "aging" of grape by increasing the content of nitrogen and carbon dioxide and reducing the oxygen content at the same time. The berries remain almost in the same condition as when they were placed in sealed boxes or containers.
A typical atmosphere is composed of about 21% oxygen, 78% nitrogen and 0.03% carbon dioxide. When using the above-mentioned method, the storage atmosphere is regulated as follows:
- Carbon dioxide (СО2) – 3-8%;
- Oxygen (О2) – 2-5%.
The remaining volume is filled up with nitrogen, which practically has no effect on storage conditions. The exact amount of carbon dioxide and oxygen depends on a grape variety.
Currently, the following technologies are used to create a gas medium and to store grapes in a regulated atmosphere:
- The technology of sharp reduction of oxygen concentration RCA (Rapid Controlled Atmosphere).
- An extremely sharp decrease in oxygen level in the storeroom for a short period of time ILOS (Initial Low Oxygen Stress).
- The technology of ethylene reduction in the storeroom LECA (Low Ethylene Controlled Atmosphere)
- Dynamically controlled atmosphere DCA (Dynamic Controlled Atmosphere)
- High carbon dioxide content (up to 30%) shock treatment (СО2 shock treatment).
As in case of usual method, the temperature in the storeroom should be kept at 0 ... + 1 ° C while relative humidity is 90%-95%.
Storage of grape
Grape is an irreplaceable product for its exceptional nutritional and healing properties that positively impact a human body. It has been proven that biologically active components in grape berries regulates the synthesis of substances. The physiological and nutritional value of grapes, which account for the most of the biochemical content, are monosaccharides (glucose and fructose), organic acids, mineral salts and microelements, cellulose, pectin, dandelion, nitrogen, dye, perfume and other substances.
As grape is a seasonal fruit, it is sold fresh only for 3-4 months. In this respect, it would be expedient to take the following steps to implement the sections of the recently adopted decisions on development of viniculture concerning the extension of consumption period of grapes:
setting up grape vinyards in all climatic zones available in Azerbaijan in order to extend consumption period of fresh grape;
cultivation of grape varieties with different ripping periods in the same vinyards (from those ripping much earlier till than those that ripe very late;
Increasing the amount of the grape stored in refrigerators in winter months.
Once stored properly, depending on grape variety, 1 kg of grapes contains 150-200 gr or more sugar in the form of glucose and fructose, 0.5-1.4% organic acids (wine, apple), itamin A (carotene), B2 (riboflavin), C (ascorbic acid), adermine and P (citrin), 0.3-1.5% mineral substances (phosphorus, potassium, iron, calcium, etc.) 0.9% protein substances, 0.3-1% and more pectin substances.
The urgency of solving the problem of maximum protection of biologically active substances in the process of storage for a long period and processing is increasing. Grape is a diet product. Therapeutic properties of grape allows it to be used in a treatment of nervous system breakdown, weakness and avitaminosis.
Storage capability of grapes means that the clusters are capable of maintaining high quality of organoleptic indicators without exposure to phytopathogenic and physiological illnesses and with no apparent loss of freshness within a few months. The storage capability indicators are output of standard product, the amount of losses and the duration of storage.
The main factor determining the long-term and successful storage of grapes is the individual characteristics of the variety. Centuries-old practice of vine-growing shows that the variety has a decisive effect on storage of the grape along with determining the quantity and quality of the product. Not all of the best table varieties are suitable for long periods of storage and for long distances. Many of them, despite their excellent taste, are not resistant to being stored due to their fragile skin. Late ripening grape varieties are usually more suitable for storage. In order to fully characterize the late ripening varieties, it is important to examine their storage capability, taste and appearance, and also study them during the storage period.
Alongside with traditional local and introductory varieties, we have also tested the storage capability of the Azeri and Ganjavi varieties created in our Institute. A brief description of these varieties is as follows:
Azeri (Katta- kurqaan x Tabriz) medium-late ripening table grape variety. It has large, 3-5 sliced and medium-cut leaves, which are dark green on the upper surface and light green on the lower surface.
Flowers are bisexual. The growing power of bushes is medium or strong and the ripening rate of sprigs is fine. They are resistant to diseases like oidium, grey decay and anthracnose. It is a highly productive variety (128-177 s/ha). The sugariness in berries totals 19-20 g/100sm³ while titrating acidity varies between 4,7-5,5 g/dm³. Katta-kurgan variety is known for its medium sized berries and more harmonic ratio of sugar and acidity.
Ganjavi (White shani and Bayanshira) is a universal late ripening variety. The leaves are large, light green, medium-cut and 5-sliced. The flower is bisexual. The clusters are big, cone-shaped and of medium density. The berries are big, juicy and sweet. The vines have strong growing power. It is resistant to oidium and grey decay. It has high productivity. The sugariness level in the berries varies between 18-19 g/100sm³ while titrating acidity varies between 5,8-6,0 g/dm³. Along with fresh use, it is suitable for the production of table wines, grape vinegar and also drying.
|
Azeri |
Ganjavi |
This variety of grape was stored in a refrigerator for three months at 0ºС with the relative humidity totalling 85%-90%. The storeroom was fumigated with sulphur anhydride every week to prevent effects of harmful microflora. Pink Tayfi variety has been selected as a control.
The results of the study are on the table :
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Variety |
Standard product output, % |
Composition of losses, % |
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|
Rotten |
Damaged |
Fallen |
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Azeri Ganjavi Tayfi |
72 60 87 |
69 100 70 |
22 30 |
9 |
As it can be seen, the control variety is far better than the hybrids we tried. It can be attributed to a storage technology especially designed for Tayfi. At the same time, it is required to clarify the impact of factors such as the ripening degree, cultivation and storing conditions, which enable a successful storage of varieties selected by Viniculture and Wine Making Scientific Research Institute. It is also important to study the indicators (transportability, natural loss of mass, change of chemical composition and microflora during storage) that determine the storage capability of a variety. In case of Azeri variety of grape, the great part of losses account for microbiological degradation, a small proportion – damaged berries while even smaller proportion accounts for berries that fall. In case of Ganjavi variety, the very rotten berries account for the losses.
Based on the findings one can conclude that it is expedient to continue studies over the above-mentioned hybrid varieties, especially on Azeri variety, the parenting forms of which possess high (Tabrizi) and medium (Katta-kurqan) storage capability, in order to develop optimal storage technology in hybrid varieties.
Under normal conditions, the main source of respiration for grape is carbohydrates. The oxygen that enters the grape berries acidifies certain part of sugar into CO2 and water through heat exposure. One should bear in mind that once the storeroom temperature has been regulated by the airing system in a timely manner, the rise in temperature of berries caused by respiration can increase the consumption of dry substances which, in turn, leads to development of microorganisms and degradation of the product.
The easiest way to protect the grape at a time of storage is to burn sulphur anhydrite in the storeroom. Once the grapes are loaded, the storerooms are closed and 5 gr sulphur is burnt per 1m³ in the storeroom. During the storage period 2.5 gr of sulphur is burned per 1m³ twice a week. In the past we used this method to store grapes grown in Absheron. Below one can find info about the efficiency of using SO2 in the indicated doses:
Changing number of microorganisms on berries during storage
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Number of microorganisms on berries (thous/1 gr berry) |
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Variety |
Untreated |
Treated with SO2 |
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When placed for storage |
When placed for storage |
After storage |
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Bacteria |
Fungi |
Bacteria |
Fungi |
Bacteria |
Fungi |
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|
Aghadayi |
16,5 |
1,7 |
7,8 |
0,2 |
0.5 |
0,06 |
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Gara shani |
69,8 |
2,4 |
22,1 |
0.5 |
0,7 |
0,05 |
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Agh shani |
153,4 |
1,2 |
61,7 |
0,8 |
4,8 |
0,6 |
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Sarı gilə |
410,0 |
2,9 |
159,4 |
1,5 |
6,0 |
1,2 |
Another common method is to protect the grape, which has been placed for storage with metabisulfide (Na2S2O5). The table below shows the impact of this method on storage capability of the grape:
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Variety |
Treated |
Treated with Na2S2O5 |
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|
Standard product, % |
Type of losses, % |
Standard product, % |
Type of losses, % |
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|
Degradation |
Falling |
Degradation |
Falling |
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Moldova |
40 |
50 |
50 |
95 |
5 |
|
|
Aghadayi |
30 |
70 |
30 |
82 |
8 |
10 |
|
Mahmudu |
35 |
50 |
50 |
86 |
14 |
|
|
Ala shani |
30 |
60 |
40 |
80 |
9 |
11 |
As shown in Table 1, the use of metabisulphite significantly weakened impact of pathogenic microflora. As you can see, the use of sodium metabisulfite has significantly reduced the impact of pathogenic microflora.
We also studied the storage of the same variety using different methods of protection. Moldova variety of grape, cultivated in Absheron Experimental Field, has been selected as a research item. It was stored in a refrigerator at 5°С for four months.
Sodium metabisulfite (Na2S2O5) and two naturally-based drugs presented by the Institute of Polymers of ANAS for an experiment were used to prevent development of a harmful microflora. Taking into account that the grape not treated with any protective substance was spoiled very quickly, we selected grape kept in 30% sugar solution as a control. When the storage time was over, the commercial analysis of the grape, which was stored using various methods, was carried out and the output of the standard product and the increased level of sugar in berries were defined through laboratory analysis.
The results of the experiment are shown in the table.
The results of storage of Moldova variety of grape for fourth months
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s/n |
The drug used |
Standard product output,% |
Sugariness, gr/cm³ |
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|
Before storage |
After storage |
Increase,% |
|||
|
1 |
№ 231 |
37,7 |
16,6 |
17,4 |
4,8 |
|
2 |
№ 234 |
52,4 |
-//- |
17,8 |
7,2 |
|
3 |
Na2S2O5 |
100 |
-//- |
18,0 |
8,4 |
|
4 |
30% sugar solution (control) |
56,7 |
-//- |
18,6 |
11,2 |
Apparently, in the option where Na2S2O5 was applied as a protection against the impact of harmful microflora, there were losses neither from degradation nor from the falling of berries from the cluster. The colour and consistency of berries remained the same as they were before being stored. Even though the colour of the cluster has slightly changed, it remains on the level suitable for the fresh grape (Picture 1).
As to the drugs experimented, 2/3 of the product in the option № 231 and slightly more than half of the product in the option № 234 was lost while using the same method.
The losses incurred by the grape kept in 30% sugar solution taken as a control were mainly observed in parts that were in contact with the air while the parts of the grape immersed in the solution and cluster kept their original colour and quality (Picture 2).
|
Na2S2O5 |
Control |
Drying the grapes
Dried grape product possesses certain nutritional and dietary properties. It contains fast digestible glucose and fructose sugars, which are about 65-80%, 1-9% organic acids, 2% mineral substances, 0,6-1,7 nitrogen substances and 0,6- 1.7% cellulose. It is also rich in microelements and vitamins that are useful to the body.
Dried grape is a highly nutritional product. The energy of 100 g of dried grapes is four times as much as 100 g of fresh grapes.
Grapes are dried to be stored for a long period of time and to facilitate its transportation. The more water is released, the higher is the density of the products remaining in the product, and thus the dried product is well stored. While drying the grape, the amount of water decreases to such a degree that microorganisms in the product stop acting under this condition. For bacteria this is 30% while for germs and mildew mushrooms it is 15-20%. The duration of the grape drying depends on the temperature, relative humidity, air movement pattern, the density and thickness of the skin, the purine-based layer on the surface, and the amount of grape harvested from the 1 m2 dried area. The commodity output of dried grapes depends on the quality of raw material, drying technology and the degree of compliance with it. depends on the factors. The application of proper dried technology ensures that taste and nutritional quality, fragrances of the product and its vitamins will be kept for up to two years.
Raison varieties with 23-25% sugar and currants variety with 22-23% are dried. In order to increase the output of dried fruit, grape fields should not be watered two weeks before the grape harvesting. This is because excessive amounts of water slow down the grape’s drying process. Grapes intended for drying are harvested and dispatched once they are technically ripe.
Grapes are dried in natural and artificial way. Aftobi Objus Soyaki and Stabel methods are used to dry the grape artificially.
Aftobi method is the simplest drying method, so no additional treatment is used for this purpose. This method is used to dry white raisins, black raisins, and fast-ripening currants varieties. Sorted grapes are dried under special conditions in special areas reserved for it. The drying time is 20-30 days. The output of the dried product is 21-23%. Its commodity name is Shahani, Bidana, Avlon, and Chilyaki.
Grapes dried by Objus method is processed additionally. It is mainly applied to varieties of black raison, white raison, Katta-Kurgan, Sultani, Nimrang and various currants varieties. Sorted grape berries are milled in a caustic soda solution and then laid in specially allotted areas to dry. After 3-4 days, the berries are turned. It takes grapes 6-12 days to dry by this method. The output of dried products is 23-26%. Products named Shahani, Germian, Shabza and Chilyaki are obtained through this method. Solar drying is not only simple, but also cost-effective. However, these methods also have disadvantages. The disadvantage of Aftobi and Objus is that a dried product is not protected against atmospheric sediments and contamination. In addition, because of the harmful effects of sunrays, grape vines get dark brown and the taste of the product worsens as a result of sugar caramelization.
The shadow or Stabel method is used to obtain high quality products from light colored grape varieties. The dried product gets golden brown with this method. Sorted open grape varieties, such as White Raisins, Katta-Kurgan, Sultani and Nimrang are boiled in caustic soda solution, then laid on wooden trays and exposed to sulfate anhydride smoke or immersed into sulphate solution. The sulphated product is dried in trays in the shadow by Stabel method.
Drying takes 14 to 24 days. The yield of dried fruit is 28-32% for kishmish variety and 26-27% for currants. The golden Germian and golden Sabzah are obtained by this drying method. The advantage of sulfurization of products is not only about the natural colour, but also the content of vitamin C in the product, in reducing sugar, and protecting the finished product against pests and microorganisms.
The artificial drying of grapes does not depend on climatic conditions and is applied in all viticulture areas. It helps to speed up the process of drying of grapes. Distribution of heat from special drying cabinets equally and ensuring gradual rise in temperature provides for a good quality product. The temperature is 80-90° C, 70-75 ° C in 1 -1.5 hours and 50° C at the end of drying. High temperatures cause the product to become caramelized and burnt.
The consistency of the juice increases as a result of water evaporation from the berries during drying. At the same time, chemical composition of the berry also changes. The ratio of sugar to acid increases, the quality of the acids changes, the proportion of different nitrogen forms increases due to rise in amount of pentose , the total amount of phenols decreases, and the amount of aldehydes increases.
Dried grape is divided into two main groups, depending on the varieties used.
1. A product obtained by drying seeded grapes is called currants.
2. A product obtained by drying seedless grapes is called a raison.
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Grape harvesting |
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Drying |
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Processing, sorting |
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Packaging |
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Sentenial Sidless variety in dried form |
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Pink raison variety in dried form (2,0) |
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Tabriz variety in dried form (natural method) |
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White raison variety in dried form (artificial method) |
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Sarıgila variety, fresh and dried |
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Sentenial Sidless grape variety |
Sentenial Sidless grape variety, new (4,0 cm), in a dried form (3,0 cm)
