Apples are one of the most popular fruits around the world. Their sweet, crunchy taste makes them a favorite snack and ingredient. But apples only last for a few weeks after being picked before they start to go bad. So how do grocers manage to keep apples fresh and delicious for months at a time?
Quick Answers
There are a few key techniques used to extend the freshness of apples for long periods:
- Controlling temperature – Apples are stored at very cold but not freezing temperatures, usually between 30-35°F (-1-2°C). This slows their respiration and other biological processes that lead to spoilage.
- Controlling atmosphere – Storing apples in rooms with low oxygen and high carbon dioxide levels further slows their ripening process.
- Wax coatings – Apples are coated in a thin edible wax which slows moisture loss and oxidation.
- Fungicide treatments – Chemical fungicides applied to the apples prevent mold growth.
- Careful handling – Bruising and damage is minimized through gentle handling and transport.
How Long Do Apples Last Naturally?
Freshly harvested apples will generally last 1-3 months when stored in cool conditions before quality starts to decline. Room temperature storage dramatically shortens this lifespan to just 1-2 weeks.
The key factors that affect apple spoilage rates are:
- Respiration – Apples respire throughout storage, using up nutrients and releasing ethylene gas which promotes ripening.
- Water loss – Moisture loss causes apples to shrink and become mealy.
- Oxidation – Exposure to oxygen causes browning of apple flesh.
- Microbes – Fungi, molds, and bacteria can grow on apples, causing rotting.
- Physical damage – Bruises, punctures, and other injuries accelerate deterioration.
Under regular conditions, these processes rapidly lead to spoilage. So slowing them down is key for prolonging freshness.
Temperature Control
The most important storage factor for apples is maintaining cool temperatures as close to 32°F (0°C) as possible without freezing.
Refrigeration slows the biological and chemical reactions related to ripening and senescence. The lower the temperature, the more dramatic the effect. Storing apples at 30°F (-1°C) can more than triple their shelf life compared to 50°F (10°C) storage.
However, freezing causes damage to apple cell structure. So temperatures must stay slightly above freezing. Ideal commercial storage temperatures for apples range from 30-35°F (-1 – 2°C).
Controlled Atmosphere Storage
In addition to refrigeration, apples destined for long-term storage are often kept in controlled atmosphere (CA) rooms. CA storage involves carefully controlling the composition of gases in the storage rooms.
Most fresh foods respire by taking in oxygen and releasing carbon dioxide. By reducing oxygen levels to 1-3% and increasing carbon dioxide to 1-5%, the respiration rate of apples can be slowed by up to 10-fold.
This dramatically inhibits the apples’ production of ethylene, reducing ripening and senescence reactions. It also prevents seed germination and fungus growth.
CA storage rooms are carefully monitored and adjusted throughout the storage season to fine tune the gas balance based on the apple variety and harvest timing. When ready for distribution to stores, the apples must be gradually re-acclimated to normal atmosphere to avoid damage.
Edible Wax Coatings
Another important step in apple storage is applying an edible wax coating. This thin layer of food-grade wax or resin forms a protective barrier around the fruit.
Wax coatings serve several purposes:
- Slow moisture loss – Reduces apple shrinkage and toughening of flesh
- Limit gas exchange – Oxygen and carbon dioxide move slower, further reducing respiration rate
- Delay oxidation – Minimizes enzymatic browning of cut surfaces
- Enhance shine – Wax fills in skin micro-cracks and enhances glossiness
Carnauba wax derived from palm leaves is most commonly used. Beeswax, shellac resin, and wood resin may also be used. Fungicides are often mixed into the wax to bolster protection against mold.
Apples to be sold fresh are typically waxed after leaving storage and before shipment to stores. This gives them extra protection through the final transportation and marketing steps. Unwaxed apples clearly show a much shorter shelf life.
Fungicide Treatments
Another key protective measure is treatment with fungicides before storage. Apples are highly susceptible to mold, rot, and other fungal diseases. Fungicide sprays create a chemical barrier to prevent infection.
Common fungicides used include thiabendazole, diphenylamine, phenylphenol, and phosphites. These compounds interfere with fungal growth and are applied as sprays or mixed into wax coatings.
Stringent regulations control which chemicals are permitted and at what levels of residue. Treatments are carefully timed and applied to control disease without impacting apple flavor.
Gentle Handling
Careful handling during harvest, storage, and transportation is also very important. Bruises, punctures, and other physical damage create entry points for microbes and accelerate moisture loss.
Apples are picked by hand to avoid damage. Specialized padded bins are used for transport from orchard to warehouse, where apples are quickly pre-cooled for storage. Conveyors, sorting machinery, and packaging areas are designed to minimize drops and compression damage.
Storage Facility Design
Sophisticated storage facilities bring all these protective measures together in ideal combinations tailored to specific apple varieties. Key design factors include:
- Refrigeration equipment to remove field heat and maintain optimum temperature
- Air handling to control oxygen, carbon dioxide, humidity, and ethylene levels
- Air filtration and sanitation to prevent mold and decay agents
- Smooth handling equipment and packaging materials
- Loading dock protections against weather and pests
- Insulation and vapor barriers keeping conditions uniform
- Monitoring and control systems to adjust for changes and collect data
These controlled atmosphere cold storage rooms provide the ideal environment to slow apple’s natural ripening and deterioration processes. Regular quality sampling and adjustments ensure optimum conditions are maintained throughout the storage period.
Storage Duration by Apple Variety
While proper storage can preserve apples for 6-12 months, some apple varieties store better than others. The table below shows typical maximum storage times for popular apple types:
| Apple Variety | Max Storage Time |
|---|---|
| Fuji | 4-6 months |
| Gala | 3-5 months |
| Golden Delicious | 5-7 months |
| Granny Smith | 6-8 months |
| Honeycrisp | 3-5 months |
| Jonagold | 5-6 months |
| McIntosh | 2-3 months |
| Red Delicious | 5-6 months |
As shown, late-harvest apples like Granny Smith hold up best, while fragile heirloom varieties like McIntosh deteriorate rapidly even in ideal conditions. Storage potential also depends on harvest timing and growing conditions each season.
Pre- and Post-Storage Care
Proper handling before and after cold storage also affects apple’s usable storage life. Key steps include:
- Rapid pre-cooling after harvest to remove field heat
- Careful sorting and defect removal prior to storage
- Gradual warming and re-acclimation to air before marketing
- Antioxidant dips to prevent cut surface browning
- Post-storage waxing for extra fungal and moisture protection
Apples destined for processing into juices, sauces, and other products are often held in regular cold temperatures rather than long-term controlled atmosphere conditions.
Conventional vs Organic Storage
Most commercially stored apples in the US are produced conventionally using integrated pest management systems. This allows fungicides and wax coatings to better preserve apples during storage.
Organic apples represent less than 5% of the total US crop. Without synthetic fungicides available, organic apples tend to have shorter usable storage lives by 1-2 months. Gentle handling, non-synthetic waxes, and careful facility sanitation are especially critical.
Recent Advances
Better apple breeding and new storage technologies continue to extend potential storage times. For example:
- New apple varieties with improved storage traits
- Dynamic CA storage responding to real-time apple respiration
- Antimicrobial edible coatings such as chitosan
- Smart sensor networks to fine-tune humidity, gases, and temperature
Researchers are also exploring low-dose irradiation and other new approaches to make apples even safer and longer-lasting.
Conclusion
Modern apple storage relies on a multi-pronged approach to dramatically slow the fruit’s natural ripening and senescence processes. Refrigeration, controlled atmosphere, fungicides, gentle handling, and protective coatings work together to enable months of storage with minimal losses. Continued research and technology improvements will further extend the fresh-picked flavor consumers can enjoy with apples, even far outside the normal harvest season.
