The moment a rose flower is picked, the clock begins to run. Although the flower can no longer obtain water or nutrients from the plant, respiration, enzyme activity, and other biological processes continue within its tissues for some time.
For this reason, harvested Rosa damascena flowers should not be treated as an ordinary dry raw material. The conditions in which the flowers are held, the temperature to which they are exposed, and the time between harvesting and distillation can influence both the quantity and chemical composition of the resulting essential oil.
The best way to preserve oil-bearing rose flowers is not to store them for an extended period, but to process them as soon as possible. Refrigeration may provide additional time when delays are unavoidable, but it cannot preserve all the characteristics of freshly harvested flowers indefinitely.
Akita Rose Academy Learning Objectives
By the end of this lesson, you will understand:
- Why fresh rose flowers should not be held unnecessarily
- What changes begin within the first few hours after harvesting
- How flowers should be handled during unavoidable short delays
- How heat and compression can contribute to fermentation
- What cold storage can and cannot preserve
- Why physical appearance and chemical quality are not the same
- How to recognize possible signs of quality deterioration
Why Do Rose Flowers Continue to Change After Harvesting?
A flower does not become biologically inactive immediately after it is removed from the plant. Respiration and enzyme activity continue in its living cells for a period of time.
After harvesting, rose flowers may gradually experience:
- Water loss
- Softening of cellular tissues
- Changes in petal colour
- Loss of volatile compounds
- Alteration of the aroma profile
- Increased microbial activity
The rate of these changes depends on temperature, humidity, air circulation, compression, cleanliness, and holding time.
Changes generally occur more rapidly in warm, humid, and poorly ventilated conditions. Cooler conditions can slow these processes, but they do not stop them completely.
Are Holding and Storage the Same?
Although these terms are related, they do not describe exactly the same practice.
Temporary holding
Temporary holding occurs when harvested flowers cannot be processed immediately because of weighing, transportation, or scheduling at the distillation facility.
Planned storage
Storage is the intentional preservation of flowers under defined conditions of temperature, humidity, packaging, and duration.
In rose essential oil or rose distillate production, the objective is not to store flowers for as long as possible. The priority is to preserve freshness and process the flowers without unnecessary delay.
Cold storage is not equivalent to fresh processing. It is a controlled preservation measure that may help slow quality deterioration when delays are unavoidable.
Why Should Fresh Rose Flowers Be Processed Quickly?
Oil-bearing rose flowers are valuable because of their volatile aromatic compounds. The term “volatile” means that these substances can evaporate and disperse into the air under suitable conditions.
Holding the flowers may affect more than their total essential oil content. The relative proportions of important aroma compounds—including citronellol, geraniol, and nerol—may also change.
It is therefore important to distinguish among three related concepts:
| Concept | Meaning |
|---|---|
| Essential oil content | The percentage of essential oil measured in a specified quantity of flowers |
| Essential oil yield | The total amount of essential oil obtained in practice from a specified quantity of flowers |
| Essential oil composition | The distribution of citronellol, geraniol, nerol, and other compounds within the oil |
A flower that retains an attractive appearance has not necessarily retained its original essential oil content or aroma composition.
Why Are the First Six Hours Important?
In Prof. Dr. Hasan Baydar’s work Oil-Bearing Rose Cultivation and Industry, freshly harvested flowers are recommended to be distilled without delay and, whenever possible, within approximately six hours.
The same source indicates that when flowers are spread on a clean, suitable surface and held briefly in a cool, shaded environment, substantial essential oil loss may not occur during the first six hours. Small fluctuations or a temporary increase in measured essential oil content may also be observed because of certain enzymatic effects.
This does not mean:
“Holding rose flowers for six hours is better than distilling them immediately.”
Six hours is not an absolute safety limit under every production condition. Flower temperature, humidity, cleanliness, air circulation, and the depth of the flower pile can all influence the outcome.
The most reliable approach is to coordinate harvesting, transportation, and production so that the flowers can be processed as quickly as possible.
How Should Flowers Be Held During a Short Delay?
If immediate processing is not possible:
- Keep the flowers away from direct sunlight.
- Use a cool, shaded holding area.
- Do not create unnecessarily deep piles.
- Do not press or crush the petals.
- Maintain adequate air circulation.
- Avoid containers that carry foreign odours.
- Prevent contact with soil or unclean surfaces.
- Record the time between harvesting and processing.
The recommendation to spread flowers on a “clean surface” should not be interpreted as placing them directly on the ground. Only clean, verified, production-appropriate surfaces or containers should be used.
Why should flowers be spread in a thin layer?
When flowers are kept in a large, compressed pile, heat generated within the pile may not dissipate efficiently.
Spreading them in a thin layer may:
- Improve air circulation
- Reduce compression
- Limit heat accumulation
- Reduce crushing and liquid release
However, flowers should not be spread indiscriminately across a large area. The holding surface must meet appropriate hygiene and production standards.
Can Rose Flowers Be Stored in Sacks?
Flowers may be placed in sacks or other collection containers during harvesting and short-distance transportation. This does not mean that they should remain inside full sacks for extended periods.
When sacks are overfilled:
- Flowers at the bottom may be crushed.
- Air circulation may decrease.
- Heat may accumulate within the flower mass.
- Moisture may condense.
- Fermentation may accelerate.
- Essential oil yield and composition may change.
The risk is particularly high when stacked sacks are left in a vehicle or exposed to the sun during warm weather.
Collection and transportation containers should be:
- Clean
- Free from foreign odours
- Suitable for the intended material
- Filled only to an appropriate level
- Designed or handled in a way that limits compression
What Is Fermentation?
In this context, fermentation is a general term for the biochemical and microbial changes that may occur when flowers are held under warm, humid, and compressed conditions.
The process may develop as follows:
- Respiration continues after harvesting.
- Compression reduces air circulation.
- Respiration and environmental heat contribute to heat accumulation.
- Crushed cells release moisture and cellular components.
- Naturally occurring enzymes continue to transform certain compounds.
- As holding time increases, microorganisms may become more active.
- The flowers’ aroma, colour, and essential oil composition may change.
The rate of fermentation is not identical in every batch. It depends on:
- Temperature
- Humidity
- Flower cleanliness
- Pile size
- Degree of crushing
- Air circulation
- Holding time
Are Enzymatic Changes and Microbial Fermentation the Same?
No. The two processes may be related, but they are not identical.
Enzymatic change
Enzymatic change refers to chemical transformations caused by enzymes naturally present in the flower’s own cells. These enzymes may remain active for some time after harvesting.
Microbial fermentation
Microbial fermentation occurs when bacteria, yeasts, or other microorganisms multiply under favourable temperature and moisture conditions and cause changes in the flower tissues.
Some enzymatic changes may begin during a short holding period. As the delay increases—particularly under warm or unhygienic conditions—the risk of microbial activity may also increase.
Short-term enzymatic change should therefore not be described as though it were the same as uncontrolled microbial fermentation.
What Happens When Holding Time Increases?
Scientific data cited in research by Baydar and Göktürk Baydar indicate that an essential oil content of approximately 0.035% in freshly distilled flowers declined to:
- Approximately 0.030% after 12 hours
- Approximately 0.027% after 24 hours
- Approximately 0.025% after 36 hours
These results demonstrate that essential oil content may gradually decline as holding time increases. However, the values apply to the flowers and experimental conditions used in the study and should not be treated as guaranteed outcomes for every production batch.
Baydar’s general assessment also indicates that holding flowers for more than 12 hours may result in an essential oil yield reduction of approximately 20%.
The essential oil does not disappear instantaneously. Losses and chemical changes develop progressively according to time and environmental conditions.
How Can Fermentation Affect Essential Oil Composition?
Holding and fermentation may affect not only the quantity of essential oil obtained, but also the relative proportions of its chemical constituents.
Studies have reported that longer holding periods may be associated with:
- Increased citronellol
- Decreased geraniol
- Decreased nerol
- Increased levels of certain long-chain hydrocarbons
- Changes in methyl eugenol
An increase in citronellol alone does not necessarily indicate an improvement in overall quality. The aroma profile of rose essential oil depends on the balance among many volatile compounds, rather than the concentration of a single constituent.
In a 2009 cold-storage study, oils obtained from stored petals showed increased citronellol alongside substantial reductions in geraniol and nerol. The researchers reported that the best essential oil content and composition were obtained from flowers distilled immediately after harvesting.
Why Is Temperature So Important?
As temperature rises:
- Flower respiration may accelerate.
- Water loss may increase.
- Cellular membranes may deteriorate more rapidly.
- Enzymatic and microbial changes may accelerate.
- Losses of volatile compounds may increase.
Baydar reports that essential oil losses may accelerate when flowers are held above 25°C. Under these conditions, citronellol and certain hydrocarbons may increase while geraniol and nerol decrease.
This does not mean that 25°C represents a precise point at which flowers suddenly deteriorate. Holding time, humidity, pile size, flower condition, and air circulation must also be considered.
What Does Cold Storage Provide?
Refrigeration can slow biological and chemical changes within harvested flowers. It may therefore provide additional time when immediate distillation is impossible.
Cold storage, however:
- Does not completely prevent essential oil loss
- Does not stop all enzyme activity
- Does not preserve the chemical composition indefinitely
- Cannot keep freshly harvested flowers permanently fresh
Cold storage should not be described as superior to immediate processing. It is a controlled preservation tool for unavoidable delays.
What did the 0–3°C storage study show?
In the study by Kazaz, Erbaş, and Baydar, oil-bearing rose petals were stored at 0°C and 3°C, at a relative humidity of 90 ± 5%, for 7, 14, 21, and 28 days.
The measured essential oil content was:
- 0.043% immediately after harvesting
- An average of 0.039% after 7 days
- An average of 0.030% after 14 days
- An average of 0.023% after 21 days
- An average of 0.022% after 28 days
The difference between the two storage temperatures was not statistically significant for essential oil content, whereas storage duration had a significant effect.
The best results were obtained from flowers distilled immediately after harvesting. Among the stored samples, flowers held at 0°C for seven days produced the results closest to those of the fresh sample.
These experimental findings do not mean that flowers can be held safely for seven days in every commercial operation. The flower quantity, packaging, humidity, temperature control, and laboratory distillation method used in the study may differ from commercial production conditions.
What did four weeks of storage at 4°C show?
In a 2008 study by Baydar and colleagues, oil-bearing rose flowers were stored at 4°C for one, two, three, and four weeks.
Over the four-week period, essential oil content reportedly declined from 0.035% to 0.010%. During the same period:
- Monoterpene alcohols such as citronellol, geraniol, and nerol decreased.
- Long-chain hydrocarbons such as nonadecane, heneicosane, and eicosane increased.
The study confirms that the value reported in the source summary is 0.035%, not 0.35%.
Even if flowers remain physically intact for four weeks, their chemical quality should not be assumed to remain equivalent to that of fresh flowers.
What Is Controlled or Modified Atmosphere Storage?
Controlled- or modified-atmosphere systems attempt to manage not only temperature but also oxygen, carbon dioxide, and moisture conditions inside the packaging.
These systems may:
- Slow respiration
- Reduce water loss
- Extend physical storage life
However, inappropriate packaging or inadequate temperature control may cause:
- Condensation
- Low-oxygen conditions
- Undesirable odours
- Microbial growth
Specialized atmosphere and packaging systems should not be confused with simple household storage methods. Their conditions must be validated for the intended use and production safety requirements.
Refrigeration and Freezing Are Not the Same
| Method | Primary characteristic |
|---|---|
| Refrigeration | Keeps flowers above their freezing point at a low temperature to slow biological and chemical changes |
| Freezing | May cause water within the tissues to freeze and form ice crystals |
| Conventional cold storage | Lowers temperature but does not necessarily control humidity or atmospheric gases |
| Controlled or modified atmosphere | Attempts to manage packaging gases and humidity together with temperature |
| Fresh processing | Processes harvested flowers shortly after collection |
Ice crystals formed during freezing can damage cellular tissues. Refrigerating flowers and storing them in a freezer are therefore not equivalent practices.
Whether freezing is appropriate for a particular production process must be investigated and validated separately.
Is Storage in Cold Water Appropriate?
Baydar’s general work refers to a traditional practice in which sacks of fresh flowers are held in cold water for several days.
This should not be interpreted as a universal storage recommendation for modern production.
Holding flowers in water requires consideration of:
- Water quality
- Microbial contamination
- Migration of water-soluble flower constituents
- Foreign odours
- Traceability
- Whether the material will be used for cosmetic or food production
Without a validated production procedure, a general recommendation to “store roses in cold water for three days” would not be appropriate.
Are Physical Appearance and Chemical Quality the Same?
No. A flower that remains pink and retains its shape has not necessarily preserved its original essential oil composition.
A flower held in cold storage may:
- Remain visually acceptable
- Have a lower essential oil content
- Contain lower proportions of geraniol and nerol
- Contain higher proportions of certain hydrocarbons
- Produce a different aroma profile when distilled
Visual and sensory observations alone cannot provide a definitive assessment of chemical quality. When necessary, analytical methods such as gas chromatography–mass spectrometry may be used.
How Can Quality Deterioration Be Recognized?
Visual signs
- Darkening of the petals
- Colour fading
- Crushing
- Excessive softening
- Stickiness
- Liquid release
- Mould or unusual surface growth
Odour-related signs
- Weakening of the characteristic fresh rose aroma
- Sour or fermented odour
- Musty or poorly ventilated odour
- A heavier or unbalanced aroma profile
Physical signs
- Heating within the flower pile
- Condensation inside the packaging
- Flowers sticking together
- Petals breaking apart easily
These observations may indicate a quality problem. However, the absence of visible deterioration does not prove that the chemical composition has remained unchanged.
Comparison of Storage and Handling Conditions
| Condition | Expected effect | Principal risk |
|---|---|---|
| Processing immediately after harvest | Helps preserve freshness and volatile compounds more effectively | Requires well-coordinated logistics and production planning |
| Short holding period in a cool, shaded area | May provide temporary protection during an unavoidable delay | Quality may change if time, temperature, or pile depth increases |
| Warm and compressed conditions | May accelerate heating and fermentation | Loss of essential oil and alteration of its composition |
| Cold storage at 0–4°C | May slow biological and chemical changes | Oil content and composition may still change over time |
| Specialized atmosphere packaging | May extend physical storage life | Incorrect gas or moisture conditions may increase microbial risk |
| Freezing | Strongly slows biological processes | Freezing damage to cellular tissues and different processing outcomes |
| Holding in water | Has been used in certain traditional practices | Hygiene, microbial contamination, and constituent-loss risks |
Household and Industrial Rose Storage Are Not Equivalent
Rose flowers kept for decoration, drying, or hobby use are not evaluated according to the same criteria as flowers intended for rose essential oil, rose water, cosmetics, or food production.
For decorative household storage, appearance may be the primary consideration. Industrial production must also evaluate:
- Essential oil composition
- Microbial safety
- Hygiene
- Traceability
- Packaging suitability
- Time before processing
Flowers stored in a household refrigerator cannot therefore be assumed to meet commercial production requirements.
Transporting Flowers from the Field to the Processing Facility
An effective transportation plan is one of the best ways to protect harvested flowers.
Before transportation
- Record the net weight of the flowers.
- Record the beginning and end times of harvesting.
- Identify the field or plot from which the flowers originated.
- Avoid overfilling containers.
During transportation
- Protect flowers from direct sunlight.
- Prevent excessive heat from developing inside the vehicle.
- Avoid excessive stacking of sacks or containers.
- Keep flowers away from fuel, chemicals, and foreign odours.
- Minimize travel time to the processing facility.
Upon arrival
- Record the delivery time.
- Inspect flower temperature and appearance.
- Separately assess batches showing crushing, heating, or undesirable odours.
- Plan the distillation order according to flower condition as well as arrival time.
Flower selection and harvesting techniques are discussed in greater detail in the Akita Rose Academy lesson, “How Are Rose Flowers Harvested?”
Common Storage and Handling Mistakes
1. Leaving flowers in direct sunlight
This can increase flower temperature, accelerate the loss of volatile compounds, and raise the risk of fermentation.
2. Overfilling sacks
Overfilling compresses and crushes the flowers and may contribute to heat accumulation.
3. Treating cold storage as unlimited preservation
Refrigeration slows change; it does not stop it.
4. Judging chemical quality by appearance alone
A visually attractive flower may already have undergone changes in essential oil composition.
5. Failing to record holding time
When the interval between harvesting and distillation is unknown, identifying the cause of a quality problem becomes more difficult.
6. Presenting cold-water storage as a general recommendation
This method should not be used without evaluating hygiene, microbial safety, and production suitability.
7. Assuming fermentation is always beneficial
Fermentation may increase certain measured constituents while reducing others. It cannot generally be said to preserve fresh-flower quality.
8. Sealing warm flowers in uncontrolled packaging
This may cause condensation, low-oxygen conditions, and increased microbial activity.
Akita Rose Academy Knowledge Box
Scientific studies generally support the following conclusions:
- The best essential oil content and composition are usually obtained from flowers distilled immediately after harvesting.
- Brief holding in cool conditions may provide additional time during an unavoidable delay.
- Warm, humid, and compressed conditions may accelerate fermentation.
- Cold storage can slow essential oil loss but cannot prevent it completely.
- Physical appearance, essential oil content, and chemical composition may change at different rates.
- Physical storage life and chemical quality are not the same concept.
Common Myths and Scientific Facts
“Rose flowers do not deteriorate in cold storage.”
False. Low temperature may slow deterioration, but it cannot stop all biological and chemical changes.
“If the flowers look attractive, their essential oil quality must still be good.”
False. Chemical changes can occur before visible deterioration or independently of appearance.
“Fermentation always increases rose essential oil.”
False. Certain constituents may increase, but total oil content and the balance of the aroma profile may deteriorate.
“The longer flowers remain in sacks, the more they mature.”
False. Warm and compressed conditions may accelerate fermentation and quality loss.
“Flowers that can be kept cold for four weeks retain their original quality for four weeks.”
False. Research shows that essential oil content and composition can change substantially during extended cold storage.
“Storing flowers produces the same result as immediate distillation.”
False. The best results in the cited research were generally obtained from flowers distilled immediately after harvesting.
Short-Term Rose Flower Storage Checklist
After harvesting
- Harvest time has been recorded.
- Flowers have been placed in clean containers.
- Containers have not been overfilled.
- Flowers have not been compressed.
- Flowers are protected from direct sunlight.
- A transportation or processing plan is in place.
During temporary holding
- The area is cool and shaded.
- Flowers are not forming a deep pile.
- Air circulation is not completely restricted.
- Flower temperature is monitored.
- No crushing or liquid release is visible.
- No undesirable odour is present.
- Holding time is documented.
Before processing
- Colour and texture have been inspected.
- The flower mass has been checked for heat accumulation.
- Flowers have been checked for sour, musty, or fermented odours.
- Unsuitable batches have been separated.
- The start time of distillation has been recorded.
Frequently Asked Questions
How long can fresh rose flowers be held before processing?
They should be processed as soon as possible. Baydar recommends distillation within approximately six hours when flowers must be held briefly under cool and shaded conditions. Six hours is not an absolute safe limit under every production condition.
Can rose flowers be stored in a refrigerator?
Small quantities may be refrigerated temporarily. However, a household refrigerator is not a validated commercial storage system. Temperature, humidity, cleanliness, condensation, and foreign odours must be considered.
How long can rose flowers remain in cold storage?
Experimental studies have examined flowers stored at 0–4°C for periods of up to several weeks. Nevertheless, both essential oil content and composition changed over time. For production quality, the best results were generally obtained from flowers processed immediately.
Can rose flowers be stored in sacks?
Long-term storage in tightly packed sacks is not recommended. Crushing, heat accumulation, and fermentation may occur.
Why do harvested rose flowers become warm?
Post-harvest respiration, compression, and restricted air circulation can cause heat to accumulate inside the flower mass.
Does fermentation increase essential oil yield?
Fermentation may change the measured proportions of individual constituents. However, longer holding periods are generally associated with lower essential oil content and an altered aroma balance. Fermentation should not be presented as a general advantage in quality production.
Can essential oil be produced from flowers that have been held?
Yes, they may still be distilled. However, the quantity and chemical composition of the oil may differ from those obtained from fresh flowers.
Why does the aroma of held flowers change?
Loss of volatile compounds, enzymatic transformations, cellular damage, and microbial activity may all alter the aroma profile.
Does refrigeration completely prevent essential oil loss?
No. Refrigeration can only slow the rate of change. Essential oil content and composition may continue to change as storage duration increases.
How can the quality of stored flowers be evaluated?
Colour, texture, temperature, and aroma can be inspected. A definitive assessment of chemical quality, however, requires appropriate laboratory analysis.
Summary
The most effective way to preserve oil-bearing rose flowers is not to store them for a prolonged period, but to process them as soon as possible after harvesting.
When a short delay is unavoidable, flowers should be kept in clean, cool, shaded, and adequately ventilated conditions. Compression, direct sunlight, and warm holding environments may accelerate fermentation and quality deterioration.
Cold storage can provide additional time, but it cannot preserve the essential oil content and chemical composition of freshly harvested flowers indefinitely. Across the cited studies, the best results were generally obtained from flowers distilled immediately after harvesting.
The principle of successful post-harvest rose management can be summarized in one sentence:
Keeping rose flowers cool is important, but no storage method can fully replace timely processing of freshly harvested flowers.
References
Baydar, H. (n.d.). Oil-bearing rose cultivation and industry. Department of Field Crops, Faculty of Agriculture, Süleyman Demirel University.
Baydar, H., & Göktürk Baydar, N. (2005). The effects of harvest date, fermentation duration and Tween 20 treatment on essential oil content and composition of industrial oil rose (Rosa damascena Mill.). Industrial Crops and Products, 21, 251–255.
Baydar, H., Kazaz, S., Erbaş, S., & Örücü, Ö. K. (2008). The effects of cold storage and drying on the essential oil content and composition of oil-bearing rose flowers. Journal of the Faculty of Agriculture, 3(1), 42–48. Article page
Baydar, H., Schulz, H., Krüger, H., Erbaş, S., & Kineci, S. (2008). Influences of fermentation time, hydro-distillation time and fractions on essential oil composition of Damask rose (Rosa damascena Mill.). Journal of Essential Oil Bearing Plants, 11(3), 224–232.
Kazaz, S., Erbaş, S., & Baydar, H. (2009). The effects of storage temperature and duration on essential oil content and composition of oil rose (Rosa damascena Mill.). Turkish Journal of Field Crops, 14(2), 89–96. Full text