Key takeaways
- Geothermal drying at 40–65 °C preserves 60–75 % of vitamin C in stone fruits such as apricots, compared with 30–40 % for open-air sun drying and 40–55 % for conventional hot-air systems operating above 70 °C — making temperature the single most influential variable in nutrient retention.
- Colour degradation (browning index) is 2–3× lower in geothermal-dried product than in conventional tunnel-dried equivalents, as measured by L*a*b* colour-space analysis, because Maillard and non-enzymatic browning reactions scale exponentially with temperature.
- Microbiological safety is significantly improved in enclosed geothermal chambers — total aerobic counts and yeast/mould loads routinely fall 1–2 log cycles below sun-dried product and consistently meet EU Regulation 2073/2005 limits without post-drying fumigation.
- Energy cost per kilogram of finished product drops by 60–80 % when geothermal heat replaces natural gas or LPG, and the carbon footprint falls from 850–1 200 kg CO₂e/tonne to 35–110 kg CO₂e/tonne — a reduction that directly affects Scope 3 reporting under CSRD.
- Shelf life extends by 4–8 months for geothermal-dried figs, apricots, and raisins compared with sun-dried equivalents at the same storage temperature, driven by lower initial water activity and reduced oxidative damage during processing.
Introduction
Geothermal drying temperature and nutrient retention data sit at the centre of every serious sourcing conversation about dried fruit in 2026. When a procurement team compares dried apricot lots from three different suppliers using three different drying methods, the temperature profile during processing is the single variable that explains most of the variance in vitamin C content, colour grade, microbial load, and shelf-life expectancy. Yet despite the importance of this variable, most commercial datasheets still describe drying method in vague terms — "sun-dried," "naturally dried," "gently processed" — without providing the temperature, time, humidity, and airflow data that would allow a buyer to make a quantitative comparison.
This article fills that gap. It presents side-by-side data for the three dominant drying methods in the global dried fruit trade — open-air sun drying, conventional hot-air tunnel drying, and geothermal drying — across six dimensions: process parameters, nutrient retention, colour and texture metrics, microbiological safety, energy and cost economics, and shelf-life stability. All data ranges are drawn from peer-reviewed food science literature and from internal process records at Turkish geothermal drying facilities operating in the Denizli–Aydin basin.
For a broader overview of geothermal drying technology and its B2B sourcing implications, see the geothermal drying B2B guide. For a deep dive into the chemistry of vitamin C preservation specifically, see geothermal drying and vitamin C — the science explained.
The three drying methods — process fundamentals
Open-air sun drying — the traditional baseline
Sun drying is the oldest and most widespread method of fruit preservation. Whole or halved fruits are spread on trays, racks, or directly on concrete or fabric surfaces and exposed to ambient solar radiation for periods ranging from two to five days in arid climates, and up to two weeks in humid or temperate regions. There is no enclosed chamber, no forced airflow, and no temperature control beyond the selection of drying season and latitude.
From a physics standpoint, the driving force for moisture removal is the vapour-pressure differential between the fruit surface and the ambient air. Solar radiation heats the fruit surface, raising the local vapour pressure and promoting evaporation. Wind provides natural convective mass transfer. But the rate of both processes fluctuates minute by minute with cloud cover, wind speed, ambient humidity, and time of day. Product temperature oscillates between 25 °C in early morning and 45–50 °C on the exposed surface at midday, with the interior of thicker fruit pieces remaining 5–10 °C cooler than the surface throughout the cycle.
This lack of control produces four well-documented problems in the food science literature. First, the extended drying time (often 48–72 hours of cumulative sun exposure) allows enzymatic and non-enzymatic browning reactions to progress extensively. Second, direct UV radiation degrades vitamin C via photolytic cleavage independent of temperature. Third, the open environment exposes product to airborne dust, insects, bird droppings, and microbial contamination — total aerobic plate counts in sun-dried fruit regularly exceed 10⁵ CFU/g. Fourth, uneven drying across a tray creates moisture gradients that promote localised mould growth during storage.
Despite these limitations, sun drying persists because its capital and energy costs are near zero. For commodity-grade dried fruit sold into price-sensitive markets, it remains the dominant method in Turkey, Iran, Afghanistan, and parts of Central Asia.
Conventional hot-air tunnel drying
Conventional tunnel dryers use fossil-fuel-fired heat exchangers (natural gas, LPG, or in lower-cost operations, coal or fuel oil) to heat ambient air to 60–90 °C before circulating it across loaded trays or conveyors at 2–5 m/s. The enclosed chamber allows some degree of temperature and humidity control, and drying times compress to 6–14 hours depending on product type, slice thickness, and initial moisture content.
The primary advantage is speed and throughput. A single tunnel dryer processing apricot halves at 70 °C with 2.5 m/s airflow can reach the target moisture content of 18–22 % in 8–12 hours versus 48–72 hours for sun drying. Throughput per square metre of floor space is 5–10× higher, and the enclosed environment reduces microbial contamination by 1–2 log cycles versus open-air exposure.
The cost is nutrient destruction. At inlet temperatures of 70–80 °C, the irreversible degradation of L-ascorbic acid through DHAA ring opening to 2,3-diketogulonic acid proceeds at 3–8 times the rate observed at 50 °C, following Arrhenius kinetics with published activation energies of 60–90 kJ/mol in stone fruit matrices. Beta-carotene isomerisation and oxidation accelerate above 60 °C. Total polyphenol oxidase activity increases with temperature until enzyme denaturation at 80–85 °C, and the Maillard browning rate roughly doubles for every 10 °C increase in processing temperature.
The result is a product that dries quickly but loses 45–70 % of its vitamin C, shows significant colour shift (higher browning index, lower L* value), and often develops the leathery surface texture associated with case hardening — where the exterior dries faster than the interior, trapping residual moisture that can cause quality deterioration during storage and transit.
For a detailed comparison of conventional tunnel drying against a newer technology, see the freeze-dried vs geothermal-dried fruit comparison.
Geothermal drying — how it works
Geothermal drying replaces fossil fuel combustion with direct geothermal heat from underground reservoirs. In the Denizli–Aydin geothermal field of western Turkey — one of the most active low-to-medium enthalpy geothermal zones in Europe — hot water at 80–120 °C is pumped to the surface and circulated through shell-and-tube or plate heat exchangers. These heat exchangers warm clean drying air to 40–65 °C before it enters enclosed stainless-steel drying chambers.
The operator controls four variables independently: drying-air temperature (adjustable by modulating the flow rate through the heat exchanger), relative humidity (adjustable via dehumidifier integration or exhaust damper position), airflow velocity (adjustable via variable-frequency-drive fans), and chamber pressure (slightly positive to prevent ambient contamination). Because the geothermal heat source flows continuously and costs essentially nothing at the well-head — the only direct energy cost is the electricity for pumps and fans — there is zero economic incentive to push temperatures above the optimal range for the product.
This is the fundamental difference between geothermal and conventional drying, and it is economic rather than technological. A gas-fired tunnel operator pays for every cubic metre of natural gas burned, creating a constant incentive to maximise temperature and minimise drying time. A geothermal operator pays only for pump electricity, making it economically rational to run at the lower temperature that maximises product quality. The technology enables low-temperature drying; the economics enforce it.
For a full treatment of the carbon footprint implications, see geothermal drying and Scope 3 carbon reduction.
Temperature and time profiles
The following table compares the core process parameters across the three drying methods for a representative stone-fruit product (apricot halves, 80–85 % initial moisture, 18–22 % target moisture).
| Parameter | Open-air sun drying | Conventional hot-air tunnel | Geothermal drying | | --- | --- | --- | --- | | Temperature range (°C) | 25–45 (variable, uncontrolled) | 60–80 (set point ± 3–5 °C) | 40–65 (set point ± 1–2 °C) | | Relative humidity (%) | 20–70 (ambient, uncontrolled) | 15–35 (partially controlled) | 20–40 (controlled via damper/dehumidifier) | | Typical drying time (hours) | 48–72 (weather-dependent) | 6–12 | 8–18 | | Airflow velocity (m/s) | 0–3 (natural wind, variable) | 2.0–5.0 (forced) | 0.8–2.5 (forced, VFD-controlled) | | Control precision | None — weather-dependent | Moderate — ± 3–5 °C, manual RH | High — ± 1–2 °C, programmable RH | | UV exposure | High — direct solar radiation | None — enclosed chamber | None — enclosed chamber |
Table 1. Process parameter comparison for apricot half drying. Data compiled from published drying kinetics studies and operational records from Turkish geothermal facilities.
The critical insight from this table is not any single parameter but the interaction between temperature and time. Sun drying operates at low temperatures but for extended periods with UV exposure. Conventional drying is fast but hot. Geothermal drying occupies the optimal middle ground: warm enough to drive efficient moisture removal, cool enough to minimise thermal degradation, and enclosed enough to exclude UV and microbial contamination.
Nutrient retention data
Nutrient retention is the metric that translates process parameters into product value. The following table presents retention ranges for five key nutrients and bioactive compounds in dried apricot, compiled from published food science studies and validated against analytical certificates from Turkish geothermal processing facilities.
| Nutrient / bioactive | Fresh baseline (mg/100 g DW) | Sun-dried (% retained) | Conventional hot-air (% retained) | Geothermal (% retained) | Notes | | --- | --- | --- | --- | --- | --- | | Vitamin C (ascorbic acid) | 8–12 | 30–40 | 40–55 | 60–75 | Most thermally labile; UV photolysis adds to sun-dry losses | | Beta-carotene | 35–65 | 45–60 | 35–50 | 65–80 | Isomerises above 60 °C; sun-dry UV loss partially offset by lower temp | | Total polyphenols (GAE) | 180–350 | 50–65 | 40–60 | 70–85 | Oxidase activity highest at intermediate temperatures | | Tocopherols (vitamin E) | 4–8 | 55–70 | 45–60 | 70–85 | Lipid-soluble; oxidation accelerated by high temp + O₂ flux | | Iron (bioavailable fraction) | 2.0–3.5 | 80–90 | 75–85 | 85–95 | Mineral not destroyed by heat; bioavailability affected by matrix changes |
Table 2. Nutrient retention across drying methods for dried apricot (Prunus armeniaca). Fresh baselines reported on dry-weight basis. Retention ranges compiled from peer-reviewed data including studies published in Journal of Food Engineering and Food Chemistry. Geothermal data validated against CoA from Denizli-basin facilities.
Several patterns deserve attention. Vitamin C retention shows the largest spread across methods because ascorbic acid has the lowest thermal stability threshold — degradation accelerates sharply above 60 °C and UV photolysis adds a temperature-independent loss pathway during sun drying. This is why vitamin C retention serves as the single best proxy for overall drying quality, as discussed in detail in the vitamin C preservation science article.
Beta-carotene retention in sun-dried product is actually higher than in conventional tunnel-dried product despite the longer drying time, because carotenoid isomerisation and oxidation are more temperature-sensitive than time-sensitive in the 25–80 °C range. However, geothermal drying outperforms both methods because it combines low temperature with UV exclusion and reduced oxygen flux.
Total polyphenol retention follows a complex pattern. Polyphenol oxidase (PPO) enzyme activity peaks at 40–50 °C and is inactivated above 75–80 °C, meaning conventional drying destroys the enzyme but also destroys its substrates through thermal oxidation. Geothermal drying at 40–65 °C allows some PPO activity early in the cycle but preserves the polyphenol pool that survives once water activity drops below the enzyme's functional range. Net retention is highest in geothermal systems.
For buyers seeking to understand how these retention figures translate into certificate of analysis values, see how to read a CoA for dried fruit.
Colour and texture metrics
Colour is the first attribute a buyer evaluates when opening a sample bag, and it is the single largest driver of grade classification and price premiums in the global dried fruit trade. The following table presents instrumental colour and texture data across drying methods, using metrics standard in food science research.
| Parameter | Measurement method | Sun-dried (typical) | Conventional hot-air (typical) | Geothermal (typical) | Consumer / buyer preference | | --- | --- | --- | --- | --- | --- | | L* (lightness, 0–100) | CIE L*a*b* colorimeter | 38–48 | 32–42 | 48–58 | Higher L* = lighter, preferred | | a* (red–green) | CIE L*a*b* colorimeter | 12–20 | 8–14 | 16–24 | Higher a* = more orange/red, preferred for apricot | | b* (yellow–blue) | CIE L*a*b* colorimeter | 18–28 | 12–20 | 24–34 | Higher b* = more yellow, natural-looking | | Browning index (BI) | BI = [100 × (x − 0.31)] / 0.172 | 85–120 | 110–160 | 55–85 | Lower BI = less browning, preferred | | Rehydration ratio (RR) | Mass after 30 min soak / dry mass | 2.2–2.8 | 1.8–2.4 | 2.6–3.4 | Higher RR = better cell-structure preservation | | Texture firmness (N) | TA.XT Plus texture analyser, 2 mm probe | 4–8 | 8–15 | 3–7 | Lower N = softer, more natural chew |
Table 3. Colour and texture comparison for dried apricot halves. L*a*b* values measured on Hunter/Minolta colorimeters. Browning index calculated per Palou et al. (1999). Rehydration ratio at 25 °C deionised water for 30 minutes. Firmness measured as peak force with 2 mm cylindrical probe at 1 mm/s crosshead speed.
The browning index data tell the clearest story. Maillard browning (the reaction between reducing sugars and amino acids) and caramelisation reactions both follow Arrhenius-type temperature dependence, with rate approximately doubling per 10 °C increase. Geothermal drying at 40–65 °C generates browning indices 35–50 % lower than conventional drying at 70–80 °C, producing visibly lighter, more vibrant product.
The rehydration ratio is a direct measure of cellular structure preservation. Higher temperatures cause more severe cell-wall collapse and protein denaturation, reducing the ability of dried tissue to reabsorb water. Geothermal-dried product rehydrates 15–40 % more than conventionally dried equivalents, which matters for food-service and bakery applications where the dried fruit will be reconstituted before use.
Texture firmness correlates inversely with temperature because case hardening — the formation of a dense, glassy surface layer when external drying rate far exceeds internal moisture migration — is more severe at high air temperatures and high airflow velocities. Geothermal drying's lower temperature and moderate airflow produce a more uniform moisture gradient, resulting in softer, more pliable finished product.
These colour and texture advantages directly translate into grade premiums. In the Turkish dried apricot market, the difference between Grade 1 (L* > 50, BI < 80) and Grade 2 (L* 40–50, BI 80–120) can represent a price premium of USD 800–1 500 per metric tonne. For detailed information about quality grading systems, see the dried fruit quality grades guide.
Microbiological outcomes
Dried fruit is a low-water-activity product, but microbial contamination during processing — particularly with xerophilic moulds and osmophilic yeasts — can cause quality failures during storage and transit if initial loads are too high. The following table compares typical microbiological outcomes across drying methods.
| Parameter | Sun-dried (typical) | Conventional hot-air (typical) | Geothermal (typical) | EU Reg. 2073/2005 limit | Test method | | --- | --- | --- | --- | --- | --- | | Total aerobic count (CFU/g) | 10⁴–10⁶ | 10²–10⁴ | 10²–10³ | 10⁵ (satisfactory) | ISO 4833-1 pour plate, 30 °C / 72 h | | Yeast & mould (CFU/g) | 10³–10⁵ | 10²–10³ | 10¹–10² | 10⁴ (satisfactory) | ISO 21527-2, DRBC agar, 25 °C / 5 d | | Coliforms (CFU/g) | 10–10³ | < 10 | < 10 | 10² (satisfactory) | ISO 4832, VRBA, 37 °C / 24 h | | Salmonella spp. (per 25 g) | Absent–detected | Absent | Absent | Absent in 25 g | ISO 6579-1 | | Aflatoxin B₁ (µg/kg) | 2–12 | 0.5–4 | 0.2–2 | 8 (dried fruit) | HPLC-FLD, IAC cleanup | | Ochratoxin A (µg/kg) | 3–15 | 1–6 | 0.5–3 | 10 (dried fruit) | HPLC-FLD, IAC cleanup |
Table 4. Microbiological and mycotoxin comparison across drying methods for dried stone fruit. EU limits per Regulation 2073/2005 (microbial) and Regulation 1881/2006 (mycotoxins). Ranges reflect published literature and Turkish processor data.
Sun drying consistently shows the highest microbial loads because the open environment permits continuous recontamination from airborne sources, insects, and direct contact with ground surfaces. Conventional tunnel drying reduces loads by 1–2 log cycles through enclosed processing, but the aggressive airflow (2–5 m/s) can redistribute surface contaminants across the batch.
Geothermal drying achieves the lowest microbial loads for three reasons. First, the enclosed, positive-pressure chamber minimises airborne contamination. Second, the moderate airflow velocity (0.8–2.5 m/s) reduces turbulent redistribution. Third, the controlled humidity environment — maintaining RH below 40 % throughout the drying cycle — suppresses microbial growth during the critical intermediate water-activity window (aw 0.3–0.7) when xerophilic moulds are most active.
The mycotoxin data are particularly significant for buyers importing into the EU or Japan, where aflatoxin and ochratoxin A limits are strictly enforced at the border. Sun-dried product from uncontrolled environments frequently exceeds the EU aflatoxin B₁ limit of 8 µg/kg, resulting in RASFF border rejections. Geothermal-dried product from enclosed facilities consistently falls well below regulatory thresholds without requiring post-drying fumigation or irradiation. For comprehensive guidance on mycotoxin limits and testing requirements, see the aflatoxin and mycotoxin limits guide.
Energy and cost analysis
The economic case for geothermal drying rests on two pillars: the near-zero marginal cost of thermal energy at the well-head, and the reduced labour requirement compared with sun drying. The following table presents a detailed cost comparison.
| Factor | Sun drying | Conventional (natural gas) | Conventional (electric) | Geothermal | Unit | | --- | --- | --- | --- | --- | --- | | Thermal energy consumption | ~0 (solar) | 3.0–5.0 | 2.5–4.0 | 0.3–0.8 (pumps + fans only) | kWh / kg product | | Fuel / electricity cost | 0 | 0.15–0.35 | 0.25–0.55 | 0.02–0.08 | USD / kg product | | Labour requirement | 15–25 | 3–6 | 3–6 | 2–5 | person-hours / tonne | | Throughput capacity | 50–200 | 500–2 000 | 500–2 000 | 300–1 500 | kg / day per unit | | Capital cost per unit | 500–2 000 | 40 000–150 000 | 50 000–180 000 | 60 000–200 000 (excl. well) | USD | | Carbon footprint | 30–80 | 850–1 200 | 500–900 | 35–110 | kg CO₂e / tonne product | | Water consumption | Negligible | 0.5–1.5 | 0.3–1.0 | 0.2–0.8 (closed-loop) | m³ / tonne product | | Pre-treatment compatibility | Sulphur dioxide fumigation | Sulphite dip, blanching | Sulphite dip, blanching | Sulphite-free or low-sulphite | Standard practice |
Table 5. Energy, cost, and environmental comparison across drying methods. Gas cost assumes USD 0.04–0.07/kWh (Turkey 2025–2026 industrial rate). Electricity cost assumes USD 0.08–0.14/kWh. Carbon footprint includes embedded emissions from fuel production and transport. Geothermal energy cost reflects pump electricity only; thermal energy from the well is essentially free at marginal cost.
The most striking figure in the table is the energy cost per kilogram. Conventional gas-fired drying at USD 0.15–0.35/kg of thermal energy represents a significant variable cost that fluctuates with global gas prices. Geothermal drying reduces this to USD 0.02–0.08/kg — essentially just the electricity to run circulation pumps and VFD fans. This 60–80 % reduction in energy cost partially offsets the higher capital expenditure of geothermal well development and heat-exchanger installation, with typical payback periods of 3–5 years at commercial scale.
Sun drying has zero energy cost but the highest labour requirement — workers must spread, turn, collect, and sort product manually over multiple days, with total labour input of 15–25 person-hours per tonne. This labour cost often exceeds the energy cost savings, particularly in regions with rising agricultural wages.
The carbon footprint differential is the variable increasingly driving sourcing decisions for European and North American brands subject to CSRD Scope 3 reporting or voluntary carbon-neutrality commitments. Switching from gas-fired tunnel drying to geothermal reduces embedded processing emissions by approximately 90 %, from 850–1 200 kg CO₂e/tonne to 35–110 kg CO₂e/tonne. For a 20-foot container of dried fruit (approximately 18 metric tonnes net), this translates to a reduction of 13–20 tonnes of CO₂e per shipment. For a deep analysis of this carbon reduction in the context of corporate ESG reporting, see carbon-neutral dried fruit — the geothermal advantage.
Shelf life and storage stability
Shelf life is the ultimate integration of all upstream process variables — moisture content, water activity, microbial load, oxidative damage, and packaging integrity. The following table compares shelf-life expectancy across products and drying methods.
| Product | Drying method | Initial moisture (%) | Water activity (aw) | Shelf life at 25 °C (months) | Shelf life at 4 °C (months) | | --- | --- | --- | --- | --- | --- | | Figs (Aydin origin) | Sun-dried | 22–26 | 0.62–0.68 | 6–9 | 12–15 | | Figs (Aydin origin) | Conventional hot-air | 18–22 | 0.55–0.62 | 10–14 | 16–20 | | Figs (Aydin origin) | Geothermal | 16–20 | 0.48–0.55 | 14–18 | 20–26 | | Apricots (Malatya origin) | Sun-dried | 20–25 | 0.58–0.65 | 6–10 | 12–16 | | Apricots (Malatya origin) | Conventional hot-air | 17–21 | 0.52–0.58 | 10–14 | 16–20 | | Apricots (Malatya origin) | Geothermal | 15–19 | 0.45–0.52 | 14–20 | 20–28 | | Raisins (Manisa origin) | Sun-dried | 14–18 | 0.52–0.60 | 8–12 | 14–18 | | Raisins (Manisa origin) | Conventional hot-air | 12–16 | 0.48–0.55 | 12–16 | 18–22 | | Raisins (Manisa origin) | Geothermal | 11–14 | 0.42–0.50 | 16–22 | 22–30 |
Table 6. Shelf-life comparison across products and drying methods. Shelf life defined as time to first detectable quality defect (off-flavour, colour change > 5 Delta-E units, or moisture migration above critical aw threshold) in sealed polyethylene/aluminium laminate packaging with desiccant sachets. Data compiled from accelerated shelf-life studies and real-time storage observations at Turkish export facilities.
Geothermal drying consistently achieves 4–8 months longer shelf life at ambient temperature compared with sun-dried equivalents of the same product. Two factors drive this advantage. First, the lower and more uniform final moisture content and water activity achieved in controlled geothermal chambers — visible in the aw column — places the product further below the critical thresholds for microbial growth (aw > 0.60 for most xerophilic moulds) and non-enzymatic browning acceleration (aw 0.55–0.75). Second, the lower thermal and oxidative damage sustained during geothermal processing means less degradation of natural antioxidants (polyphenols, tocopherols, carotenoids) that protect the product against lipid oxidation during storage.
For B2B buyers managing long supply chains — ocean freight from Turkey to North America takes 4–6 weeks, and retail distribution adds another 2–4 months before product reaches the consumer — the difference between 6 months and 14 months of ambient shelf life is not theoretical. It is the difference between reliable product quality at end of shelf life and elevated complaint and return rates.
For a broader overview of Turkish dried fruit quality systems and how they relate to shelf-life guarantees, see the wholesale dried fruit Turkey sourcing guide.
Why Arovela chose geothermal — the business case
Denizli geothermal field advantages
Arovela's geothermal drying operations are located in the Denizli–Aydin geothermal zone of western Turkey, one of the highest-enthalpy geothermal fields in Europe. The field supplies hot water at 90–120 °C from wells drilled to 300–1 500 metres depth, providing a stable, continuous heat source that operates 8 760 hours per year with no seasonal variation.
This geographical advantage is not replicable in most other dried-fruit-producing regions. Turkey's unique combination of abundant stone-fruit agriculture (the world's largest apricot producer, second-largest fig producer, fourth-largest grape producer) and accessible geothermal resources in the same Aegean and western Anatolian region creates a sourcing advantage that no other origin can match at equivalent cost.
The Denizli field is also among the most mature geothermal districts in Turkey, with well-developed infrastructure for heat distribution, established regulatory frameworks, and a local workforce experienced in geothermal-agricultural applications. This maturity reduces operational risk and ensures consistent product quality — a critical consideration for B2B buyers committing to annual supply agreements.
Scalability for B2B volumes
A single geothermal drying facility in the Denizli basin can process 300–1 500 kg of fresh fruit per day per drying chamber, with facilities typically operating 6–12 chambers in parallel. Annual throughput capacity at a commercial facility ranges from 500 to 3 000 metric tonnes of finished dried product — sufficient to supply multiple 20-foot container orders per week during peak season.
This scalability addresses one of the most common concerns B2B buyers raise about geothermal drying: whether it can deliver the volumes required for industrial ingredient supply, private-label retail programmes, or food-service distribution. The answer, supported by operational data from existing Turkish facilities, is that geothermal drying is no longer a boutique or experimental process. It is a commercial-scale technology producing thousands of tonnes annually.
For buyers interested in private-label programmes specifically, see the geothermal-dried fruit vs conventional snack brands article for format and positioning guidance.
Third-party validated claims
Every data point presented in this article — vitamin retention, colour metrics, microbiological loads, shelf-life stability — is verifiable through third-party laboratory testing. Arovela provides full certificates of analysis (CoA) with every commercial lot, issued by accredited laboratories (ISO 17025) and covering nutritional composition, microbiological parameters, mycotoxin levels, heavy metals, and pesticide residues.
This commitment to transparent, verifiable data is the foundation of trust in B2B relationships. Claims about "gentle drying" or "natural processing" are meaningless without analytical evidence. Buyers evaluating any supplier — including Arovela — should insist on seeing lot-specific CoA data that substantiates every quality claim. Our certifications page provides an overview of the standards and accreditations underpinning our quality system, and the how to read a CoA guide explains how to interpret analytical results in a sourcing context.
For information about sustainable agriculture practices and ESG integration across the supply chain, see our sustainable agriculture and geothermal ESG overview.
FAQ
Does geothermal drying work for all types of fruit?
Geothermal drying is technically suitable for any fruit, vegetable, or herb that can be processed by convective air drying, because the fundamental mechanism — warm air circulated over the product to drive evaporative moisture removal — is identical to conventional hot-air drying. The difference lies only in the heat source and the resulting temperature profile. Fruits with high initial moisture content and heat-sensitive bioactive compounds — stone fruits such as apricots, peaches, and plums; berries including mulberries and sour cherries; and figs — benefit most from geothermal processing because the 40–65 °C temperature window preserves thermolabile vitamins and pigments while still achieving adequate drying rates. Tropical fruits processed from imported raw material, such as mango and pineapple, are also well suited. Harder commodities like raisins and prunes, which are less sensitive to temperature, still benefit from the improved colour preservation and lower energy cost. The only practical constraint is geographical: the drying facility must be located within economic piping distance of a geothermal well, which currently limits commercial geothermal drying to regions with accessible geothermal resources such as western Turkey, Iceland, and parts of New Zealand.
What temperature range is optimal for vitamin C preservation in dried fruit?
The optimal drying temperature for maximising vitamin C retention is 40–55 °C for most fruit types. At this range, the rate constant for irreversible ascorbic acid degradation — specifically, the hydrolytic ring opening of dehydroascorbic acid (DHAA) to 2,3-diketogulonic acid (2,3-DKG) — remains 3–8 times lower than at 70–80 °C, following Arrhenius kinetics with activation energies of 60–90 kJ/mol in fruit matrices. Published studies on apricot drying report vitamin C retention of 65–80 % at 50 °C versus 35–50 % at 70 °C, all other variables being equal. However, drying at temperatures below 40 °C is not recommended because the extended drying time (often exceeding 36 hours) creates prolonged exposure to the intermediate water-activity zone (aw 0.3–0.7) where oxidation rates are highest. The 40–55 °C window optimises the trade-off between thermal degradation rate and total exposure time, minimising the time-temperature integral that determines total vitamin C loss. Geothermal systems are ideally suited to maintain this temperature range because the constant heat source eliminates the temperature fluctuations that occur in solar-dependent systems.
How does geothermal drying affect shelf life compared to sun drying?
Geothermal-dried fruit consistently achieves 4–8 months longer shelf life at ambient temperature (25 °C) compared with sun-dried equivalents of the same product and origin. Three mechanisms drive this advantage. First, the controlled chamber environment produces lower and more uniform final moisture content (typically 15–19 % for apricots vs 20–25 % sun-dried) and water activity (aw 0.45–0.52 vs 0.58–0.65), placing the product further below the critical thresholds for microbial growth and accelerated non-enzymatic browning. Second, the enclosed processing environment reduces initial microbial load by 1–3 log cycles, meaning fewer organisms are present to initiate spoilage during storage. Third, the lower thermal and oxidative damage during geothermal processing preserves more of the natural antioxidant compounds (polyphenols, tocopherols, carotenoids) that protect against lipid oxidation during long-term storage. In accelerated shelf-life studies at 35 °C and 75 % RH, geothermal-dried Malatya apricots showed first detectable off-flavour at 8–10 months versus 4–5 months for sun-dried equivalents from the same harvest lot.
Is geothermal-dried fruit considered "raw" for raw food labelling?
The answer depends on the specific temperature profile used and the regulatory or certification standard applied. Most raw food certification bodies and retailer standards define "raw" as processed below 42–48 °C, though the exact threshold varies. Geothermal drying systems can be operated within this range — the temperature is fully adjustable by modulating the flow rate through the heat exchanger — but standard commercial geothermal drying of most fruits operates at 45–65 °C to achieve acceptable drying rates and food-safety outcomes. At the lower end of the geothermal range (40–48 °C), product can legitimately qualify as raw under most certification schemes, though drying times extend to 18–30 hours and throughput decreases proportionally. Buyers requiring raw-certified product should specify this in the procurement contract so the facility can adjust temperature protocols accordingly. It is worth noting that even at 48 °C, geothermal drying still provides substantial nutrient-retention advantages over conventional methods at 70–80 °C — the vitamin C retention difference between 48 °C and 65 °C geothermal processing is approximately 5–12 percentage points, while the difference between 48 °C geothermal and 75 °C conventional is 25–40 percentage points. The raw-food temperature threshold is not the primary driver of the nutrient advantage.
What is the carbon footprint difference between geothermal and conventional drying?
The carbon footprint of geothermal drying is approximately 90 % lower than natural-gas-fired conventional drying on a per-tonne-of-product basis. Independent life-cycle assessment data from Turkish geothermal operators report 35–110 kg CO₂e per tonne of dried product for geothermal processing (including pump electricity, facility construction amortisation, and maintenance), compared with 850–1 200 kg CO₂e per tonne for natural-gas-fired tunnel drying and 1 100–1 450 kg CO₂e per tonne for LPG-fired systems. For a standard 20-foot container of dried fruit (approximately 18 metric tonnes net), switching from gas-fired to geothermal processing reduces embedded emissions by 13–20 tonnes of CO₂e per shipment. This reduction falls directly into the Scope 3, Category 1 (purchased goods and services) reporting line for downstream buyers subject to the EU Corporate Sustainability Reporting Directive (CSRD) or voluntary frameworks such as CDP, SBTi, or GHG Protocol. For brands pursuing "carbon-neutral product" positioning or retailers requiring supplier-level carbon data, geothermal-dried sourcing provides a documentable, auditable emissions reduction that requires no offsets and no renewable energy certificates — the thermal energy is inherently renewable at the well-head.
Source geothermal-dried fruit
The data in this article are not abstract — they describe the products Arovela ships to B2B buyers on every continent. If your procurement team is evaluating drying methods and wants to see the numbers on an actual CoA rather than in a journal article, request a sample with full analytical documentation.
View the geothermal-dried fruit range →
For volume enquiries, private-label development, or technical questions about any data presented in this article, contact our wholesale team directly.
External references: Demiray, E. and Tulek, Y. (2017). Degradation kinetics of ascorbic acid in apricots during hot air drying. Journal of Food Engineering, 202, 44–51. doi:10.1016/j.jfoodeng.2017.01.019. International Energy Agency (2024). Geothermal Energy Technology Roadmap. iea.org/reports/geothermal.