Cold Storage for Potatoes and How Does It Work?

How Cold Storage Proves Beneficial in Storing Potatoes for Prolonged Period

For huge quantities of potatoes, it is important to have appropriate storage space for prolonged shelf life. Without a cold storage facility, potatoes are prone to diseases, bruising, sprouting, and even dehydration. These can lead to considerable loss and affect customer satisfaction.

Moreover, several processes such as respiration, transpiration (loss of water content due to heat), poor handling, improper packaging, inappropriate storage temperature and relative humidity can lead to weight loss in potatoes.

Cold storage is equipped with the equipment to control the temperature, relative humidity, and air circulation to maintain the best storage conditions. This means the produce not only appears fresh from the outside but is also healthy from the inside.

Factors Affecting the Cold Storage for Potatoes

Temperature

The storage temperature depends on various factors including will the potatoes be processed further, or sold as fresh produce or as seed, the duration of the storage, the presence of any disease or infection, the extent of damage at the time of harvesting, etc.

Moreover, the storage temperature affects the curing or healing, spreading of disease, starch-sugar conversion (Millard reaction), preparation, and sprouting.

Humidity

Usually, around 95% relative humidity levels are maintained at all times. These levels are critical in wound healing during the curing process. Plus, >90% relative humidity levels also help minimize weight loss.

Air circulation

Usually, air circulation is not required during the curing process. The heat and moisture from potatoes support the healing. It may be required in case there is free moisture is produced during storage to maintain the required temperature and humidity levels across the produce.

Usually, humidified air and/or heated or cooled air is passed throughout the produce. However, the presence of dirt and clods can affect the air movement as they form a barrier.

How Does Cold Storage for Potatoes Work

A typical process for cold storage of potatoes includes the following steps:

1. Drying
2. Curing
3. Gradual cooling
4. Appropriate storage

Let us discuss how each of these steps in detail and how different factors play a role in prolonging shelf-life and quality.

Drying

This is a critical step to store potatoes. The objective is to remove the dust and to dry the skin of potatoes but not from the inside. Usually, many producers would store potatoes with slight dust from the field to protect them and brush off the thin layer of dust before they leave the cold storage room or facility.

Potatoes are dried at around 25°C and at 85% relative humidity. In cases of extreme conditions, they may need humidification during the drying process to avoid excessive dehydration. The step is considered completed when there is no visible moisture on the potato and it feels cool but not moist.

Curing

Sometimes, the potatoes may get damaged during harvesting, handling, or transportation. Therefore, to help them heal the wounds on the skin, they are kept for 7—10 days at 15°C and 95% relative humidity. This step requires an efficient humidification system and improves their storage life by decreasing the risk of infections.

However, if there is a risk of late blight, it is advised to stop the curing process and the potatoes must be removed immediately and stored at an appropriate temperature.

Gradual cooling

After drying and curing, the next step is to gradually lower the storage temperature of potatoes. During this process, the objective should be to reduce weight loss and, therefore, the temperature is lowered by 0.3 to 0.5°C per day. The most important thing to note here is that the temperature is not increased during this step. If the potatoes are warmed due to a sudden increase in temperature, it may lead to germination. That is why the air used should have a sufficient cooling capacity, around 85% relative humidity, and it should not be more than two degrees colder than potatoes.

Thus the cold storage room especially should have insulated doors and an efficient refrigeration unit with condensers and humidifiers to consistently maintain the required conditions.

Storage

Once all these steps are completed perfectly, the storage itself becomes quite easy. Depending on the final usage or destination, the storage temperature may vary for potatoes. Usually,

• Potatoes for chips are stored between 7 and 10°C
• Potatoes for french fries are stored between 5 and 6°C
• Seed potatoes are stored between 4 and 5°C
• Potatoes for fresh/direct consumption are stored between 4 and 7°C
• Potatoes for starch and flake are stored between 4 and 5 °C

Moreover, relative humidity of 90% is required in a dark storage environment.

Now, there is an important that you wouldn’t want to miss. When potatoes are chilled to 5 to 8 °C, the Millard reaction takes place, converting starch to reducing sugars. These sugars cause brown discolouration and bitterness if the potatoes are reheated inappropriately after storage. Plus, the chips and fries made from such potatoes are not crisp but soft and infirm.

Now, it is important to increase the temperature of potatoes after storage. This is primarily done for two reasons. Firstly, it helps avoid Millard reaction and allows time for starch to reconstitute and secondly, to avoid condensation when the potatoes leave the cold storage facility.

Finally, to avoid germination during storage make sure to maintain the temperature. usually, the higher the temperature, the higher the chances of germination or sprouting. Usually, potatoes stored below 5°C do not sprout.

Final Words

Potato cold storage is essential for quality and prolonged shelf-life before the produce reaches the end customers. The combination of various factors including temperature, relative humidity, and air circulation have an impact on the drying, curing, cooling, and storage of potatoes with each step requiring an appropriate environment to avoid weight loss, disease spread, and browning.

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