Technology and organization of sun drying for seedless grape cultivars

Setting Up a Drying Yard and Resource Calculation

Air-sun drying of seedless (kishmish) and raisin cultivars allows for the production of high-quality goods with minimal energy consumption. To organize the process, non-arable land near the vineyard is selected—southern slopes or level, well-lit, and well-ventilated plots with convenient access roads are optimal. The surface of the yard is thoroughly compacted and concreted or covered with a clay-adobe solution.

• Fresh grape load per 1 m² — 10–12 kg
• Number of yard cycles per season — 2–3

For the smooth operation of a drying facility, it is necessary to prepare the infrastructure and calculate the volumes of supplies in advance. The site area should accommodate a receiving point under a canopy, blanching and sulfitation units, a canopy for shade drying, a warehouse for storing equipment and finished products, as well as utility rooms.

Drying Technologies: Obdzhush, Aftobi, and Shade Methods

Depending on the grape cultivar and requirements for the visual quality of the finished product, three main technological schemes of drying are used. Classic sun-drying methods (obdzhush and aftobi) differ in the use of blanching, which accelerates moisture evaporation by creating micro-cracks in the skin. To obtain premium-quality raisins, treatment with sulfur dioxide gas or acid is applied, followed by final drying in the shade.

For the obdzhush method, a two-boiler furnace (boiler volume 200–300 l) is installed on the drying yard next to the receiving and sorting point. The upper edges of the boilers are set at ground level for convenience and equipped with safety railings. The processing and layout process includes the following stages:

1. Sorted grapes are placed in 3–4 kg amounts into metal mesh or wicker baskets.
2. The baskets are dipped into a boiling 0.2–0.4% caustic soda solution (3–4 g of soda per 1 l of water) for 3–6 seconds until a uniform network of cracks forms on the skin.
3. Clusters are laid out on wooden trays in a single layer.
4. The trays are placed in the sun, leaving 0.5–0.6 m wide passages between rows.

For the shade drying method, the initial stages are similar to the obdzhush method, but after blanching, the grapes must be treated with sulfur. This protects the raw material from pathogenic microflora and preserves the natural golden color of the berries. Fumigation is carried out in an airtight chamber, with strictly measured dosing of sulfur dioxide gas from cylinders or by burning sulfur.

Adherence to the specified fumigation rates ensures that the residual sulfurous acid content in the finished product does not exceed the sanitary limit of 0.01%.

For shade drying, grapes treated with sulfur anhydride are stacked under a canopy with 15–18 trays per stack. The top tray is covered with an inverted empty tray to protect the product from direct sunlight. The shade method allows for an increase in the finished product yield due to the preservative effect of sulfurous acid.

Artificial Final Drying Technologies and the Soyagi Shade Method

When processing grapes using the wet sulfitation method, sun-drying is permitted. This technique helps to significantly accelerate the natural dehydration of the berries on the yard. The finished product in this case retains a beautiful golden color, although it acquires a darker shade.

Artificial drying with hot air minimizes the farm's dependence on weather conditions. The method is currently at the engineering development and industrial testing stage, but it already addresses important practical tasks. In regions with a humid climate, this is the only way to obtain high-quality raisins, and in traditional viticulture zones, drying installations are used at the end of the season to bring the product to standard moisture levels when natural air temperatures drop.

For drying, shaft (SVP-5), steam-conveyor (SPK-20, SPK-90), or tunnel dryers are used, including imported equipment of the TSER brand from the "Chachak" company. The drying time depends on the size of the berries, skin density, pulp consistency, and preliminary preparation — blanching or treatment with sulfur dioxide. To obtain high-quality raw material, it is necessary to strictly control the heat supply.

• Initial drying temperature — 60–75 °C
• Final temperature — 50 °C
• Artificial drying time — 11–24 h
• Dryer productivity — 3–12 t/day
• Labor costs per shift — 3–6 people
• Product yield when using the soyagi method — 22%

For mountainous regions, the original shadow drying method — soyagi — is suitable. It is used only for the Kishmish Belyi cultivar, the berries of which have a characteristic emerald-greenish color. The technology allows for the complete preservation of this natural shade in the finished product. The entire process takes 8 weeks.

To dry using the soyagi method, it is required to prepare a special facility:

1. Build an adobe building on a windy mountain slope.
2. Make a staggered grid of slit-like openings 70 cm long and 12 cm wide in the walls around the entire perimeter.
3. Install the entrance door strictly on the north side of the building.
4. Install vertical wooden frames inside from floor to ceiling.
5. Attach cross rails or stretch wire at a distance of 20–30 cm from each other for hanging grape clusters.

The name of the finished dry grape is strictly tied to the technology and raw material. It is determined by the ampelographic cultivar — seedless (kishmish) or raisin. The chosen drying method also influences the trade name.