Post-harvest Cooling of Asparagus
Asparagus have been used for food and medicine for thousands of years in a variety of cultures. Ancient Egyptians, Greeks and Romans all utilized the vegetable. While asparagus is in season during the spring, the Greeks and Romans dried and even froze the vegetable for use in major festivals. The oldest existing recipe book contains an asparagus recipe. Today, the vegetable remains a staple in cultures around the world and is a central feature on spring menus in an array of restaurants. Like other fresh foods, asparagus must be properly cooled and stored to maintain quality after harvest.
General Facts About Asparagus
Officially known as asparagus officinalis, asparagus was originally classified as part of the lily family of vegetables and plants along with garlic and onions. However, the family was later split, and onion varieties have been classified as Amaryllidaceae while asparagus are now Asparagaceae.
The plant is native to Northern Africa, Western Asia and most of Europe and is an herbaceous perennial plant. Only young shoots are used for food because once they begin flowering they become too woody for consumption. Varieties grown in northwestern Europe are most prominently white, and are extraordinarily popular in the region. They are tenderer and less bitter than the more widely produced green stalks. The thickness of the stem indicates the age of the plant. The plant consists of about 93% water and is extremely low in calories and sodium, making asparagus a healthy dietary choice.
General Information About Cooling and Storing Asparagus
Asparagus can require up to three growing seasons before they are ready to harvest. Once spears begin to show, they can be harvested for 2-3 weeks. Asparagus spears continue to age after harvesting. Therefore, it is important to harvest them when they are young. Because of the restrictive harvest requirements, it is vital to properly store the asparagus. There are several things to consider when storing the vegetable.
Pre-cooling – Pre-cooling is important in the storage of most vegetables because you want to remove the ambient heat as soon as possible for lengthened storage time. Asparagus’s high respiration rate requires that it be cooled to its lowest temperature as quickly as possible. Therefore, asparagus should be precooled either with hydrocooling or package icing for optimal results.
Temperature – The plant should be stored at a range of about 32°F – 35°F. Asparagus should not be stored at a temperature lower than 32°F because doing so can result in chilling injury, substantially changing the flavor of the vegetable.
Relative Humidity – Because of their substantial water make up, asparagus can easily become dried out during the refrigeration process if care is not taken. Therefore, it is important to maintain a substantially high relative humidity of 95% – 100%. This relativity can be accomplished through a variety of moisturizing techniques. However, asparagus can be susceptible to microbial infection, so there must be a delicate moisture balance during refrigeration.
Shelf Life – Asparagus have a medium-range storage life compared to other produce and can be stored for about 14 – 21 days under ideal conditions.
Ethylene Sensitivity – Due to its ethylene sensitivity one rotting, bad, or aging asparagus can greatly affect the life span of the other vegetables stored with it. This makes it important to carefully sort asparagus and to keep them separate from other ethylene-producing fruits and vegetables.
Methods for Cooling Asparagus
Hydro-cooling – This technique immerses harvested asparagus spears in cold water, quickly and efficiently reducing the temperature of the plant. While this technique is the most effective in reducing temperature, it is not the most energy efficient. However, thermal immersion systems can substantially increase efficiency. In addition, it is important to add a form of disinfectant in the water to decrease the potential for the spread of disease throughout the crop.
Ice Packaging – Both top and liquid icing are beneficial for quickly and efficiently cooling densely packaged or palletized harvests. Liquid icing allows asparagus being cooled in their packaging containers through vents and handholds. This technique prevents the need to open and remove plants from the packaging. Top icing also allows the product to remain packaged, as crushed ice is added through the top of the container. Both methods can be completed by hand or by machine. The technique is particularly beneficial for high respiration vegetables like asparagus.
The storage of your harvest is essential in ensuring that your customers receive the best possible products. As an industry expert in storage and cooling systems, SEMCO/SEMCOLD LLC works intimately with its clients to provide the perfect equipment for each producer’s individual needs. We have the necessary experience and resources to design optimal cooling and storage systems for your asparagus or other harvested crops.
