ASPARAGUS STORAGE QUALITY
Receiving Information: Asparagus should be fresh and firm with compact tips. Spears should be straight and round, and snap easily when bent. Avoid asparagus with wilted appearance or spreading tips. Dull gray-green color; limp tips: indication of chill injury. Tough spears: sensitive to ethylene; spears may become tough if exposed to the gas. For best results store away from ethylene producing fruits. Decay; tough texture; loss of flavor: will deteriorate and lose flavor if stored at high temperatures. Dried cut ends: may become dry if exposed to low humidity.
Storage/Handling: Temperature/humidity recommendation for short-term storage of 7 days or less: 32-36 degrees F / 0 - 2 degrees C. 90 - 98% relative humidity. To promote better shelf life stand asparagus cut-end down in 1-inch water.
Green Asparagus is the predominant type for fresh availability. Characterized by green stalks with some white at the base; green tips with some purple tinge. Asparagus has been in cultivation over 2,500 years, and in the United States since the 1870’s. The Greeks and Romans valued asparagus for medicinal purposes – treating bee stings, heart ailments and toothaches. Asparagus continues to grow after it is picked by using the water content of the stalk; that is the reason it is packed in pyramid boxes.
ASPARAGUS GRADING AND QUALITY TESTS
Grades of Asparagus
U.S. No. 1 consists of stalks of asparagus which are fresh, well trimmed, and fairly straight; which are free from decay and free from damage caused by spreading or broken tips, dirt, disease, insects, or other means.
a. Size. Unless otherwise specified, the diameter of each stalk is not less than one-half inch.
b. Color. Unless otherwise specified, not less than two-thirds of the stalk length shall be the color of the lot.
c. Tolerances. In order to allow for variations incident to proper grading and handling, the following tolerances, by count, are provided as specified:
1) For defects. 10 percent for stalks in any lot which fail to meet the requirements of this grade other than for trimming, including therein not more than 5 percent for defects causing serious damage: Provided, That not more than one-fifth of this latter amount, or 1 percent, shall be allowed for stalks affected by decay. In addition, not more than 10 percent of the stalks in any lot may fail to meet the trimming requirement.
2) For off-size. 10 percent for stalks in any lot which fail to meet the specified diameter or length requirements.
U.S. No. 2 consists of stalks of asparagus which are fresh, fairly well trimmed, and not badly misshapen; which are free from decay and free from serious damage caused by spreading or broken tips, dirt, disease, insects or other means.
a. Size. Unless otherwise specified, the diameter of each stalk is not less than five-sixteenths inch.
b. Color. Unless otherwise specified, not less than one-half of the stalk length shall be the color of the lot.
c. Tolerances. In order to allow for variations incident to proper grading and handling, the following tolerances, by count, are provided as specified:
1) For defects. 10 percent for stalks in any lot which fail to meet the requirements of this grade other than for trimming, including therein not more than one-tenth of this tolerance, or 1 percent, shall be allowed for stalks affected by decay. In addition, not more than 10 percent of the stalks in any lot may fail to meet the trimming requirement.
2) For off-size. 10 percent for stalks in any lot which fail to meet the specified diameter or length requirements..
ASPARAGUS QUALITY GUIDELINES
Asparagus Harvest and Grading
Asparagus is one of the first field-grown Indiana vegetables on the market. This article reviews harvest, grading and postharvest care recommendations to help you start the season with top quality asparagus.
Getting quality asparagus to market means making sure to pick good spears at the right time, grade according to your market requirements, and keep the spears cold, moist and upright.
Plan to harvest early in the morning when it is still cool. Spears to be sold should be tight at the tip, dark green, and at least 3/8 inch in diameter. During the harvest season the only spears left standing in the field should be those you expect to harvest in the future. Don’t let unmarketable spears continue to grow and develop into fern. They can harbor diseases and insects, and also slow growth of new spears.
The grading of spears after harvest will depend on your market. The USDA standards presented here provide a reference for comparison to your grading criteria, whether or not your market requires USDA standards. The best asparagus is fresh (not wilted), straight, green (or other specified color) for most of the stalk length, and has a tight tip that is not spreading. The butt end is smooth and flat. Table 1 below summarizes the USDA standards for No. 1 and No. 2 grades, and Table 2 shows the various diameter classifications defined by USDA. According to USDA standards, minimum spear length may be specified to the nearest 1/2 inch but is not required. Spears are typically 7 to 9 inches. Figure 1 illustrates USDA criteria for asparagus.
ASPARAGUS QUALITY SYSTEM
Asparagus is a perennial crop that produces spears year after year for 10 to 15 years or longer if the plants are given adequate care. Because it remains in the same location for many years, it’s important to select a planting site that’s convenient, as well as having good growing characteristics in mind. The edge of a garden might be preferable to the middle to accommodate future gardening activities.
Asparagus is grown for its succulent, immature shoots that, if allowed to grow, will eventually become the bushy foliage called ferns. In southern New Hampshire the young spears emerge about the first week in May or when the soil temperature reaches about 40 degrees F. Growth continues into late fall or early winter until the ferns are killed by frost.
The asparagus plant is made up of top (ferns), crown (buds) and roots. All three are vital to a productive plant. The ferns are the “factory,” which, through the process of photosynthesis, produces food stored in the crown and roots below ground. The number of vigorous spears in the spring depends upon the amount of food produced and stored in the crown during the preceding summer and fall. Producing a good crop of ferns is necessary to ensure a good crop of spears the next spring.
Do not cut back the old ferns at the end of the season until they are completely dead. In the fall, nutrients move from the dying ferns to the crown. Removing the ferns too early weakens the crown and may thereby reduce the size and number of spears the following spring.
Site - Full sun is ideal. Asparagus needs at least 8 hours of sun per day. Since asparagus is a long-lived perennial, do not plant where trees or tall shrubs might eventually shade the plants or compete for nutrients and water.
Soil - The crown and root system can grow to an enormous size: 5 to 6 feet in diameter and 10 to 15 feet deep. Therefore, where possible, select a soil that is loose, deep, well-drained and fertile. On sites with poor soil, incorporate manure, compost, and/or green manure cover crops into the soil before you plant asparagus.
Fertilizer - Have soil tested before planting and every three years thereafter. Soil testing can be done through a number of private and public labs. UNH Cooperative Extension offers this service. Forms and instructions are available on our website, or you can call our Info Line at 1-877-EXT-GROW (1-877-398-4769).
Adjust the soil pH to 6.5 to 6.8 by adding the appropriate quantity of limestone or wood ashes as recommended by a soil test. Fertilizer requirements are also determined by the same soil test. A general recommendation is to add the equivalent of 2.5 pounds of 10-10-10 fertilizer per 100 square feet. All lime and fertilizer materials should be thoroughly incorporated into the soil to a depth of 10 to 12 inches before planting.
The border between this row of asparagus and the adjacent lawn is tilled throughout the season, every 3-4 weeks to prevent grasses and other weeds from creeping in and taking over the planting.
Asparagus is planted in the spring. The simplest method is to plant one-year-old crowns purchased from local garden dealers or through home garden catalogs. Even though the young crown will appear to be a lifeless mass of stringy roots, it will begin to send up small green shoots (spears) shortly after planting.
Set plants 18 inches apart in rows five feet apart. Dig holes or trenches about 8 inches deep and 10 inches wide. Spread the roots in the bottom of the hole or trench and cover the crown with about 2 inches of soil. As the young shoots continue to grow during the first summer, gradually fill in the hole with soil. The tops of the crowns should be about 6 inches below the soil surface when the trenches are completely filled. This allows for cultivation by hoe or rototiller and also provides a sufficient depth of soil for new buds to develop on top of the crown.
An alternative to using one-year-old crowns is to start asparagus transplants from seeds as you would start other vegetable transplants. About 6 to 8 weeks before planting, sow the seeds directly into pots. Thin to one plant per pot and, after all danger of frost has passed, plant the young seedlings as described above for crowns. Do not cover the young shoots (ferns) with soil.
Asparagus crowns are planted in trenches 10 inches wide and 8 inches deep (top). As the young shoots start to grow, continue to add small amounts of soil to fill in the trench without burying the young ferns (bottom). By the end of the season, the trench should be filled to the top.
Weeds are the most common problem in asparagus plantings, because they compete with the crop and reduce productivity.
Do not plant asparagus or any vegetable in an area heavily infested with quackgrass or other weeds that spread by rhizomes. If necessary, begin a year in advance to clean out the quackgrass, either by hand or mechanical cultivation or by spraying with an approved herbicide when the grass is 6 to 8 inches tall. If using herbicides, follow label directions precisely for safety and good weed control. In addition to planting in an area free of weeds, it can be helpful to maintain a tilled border around the asparagus planting, to prevent weeds from outside the patch from migrating into the planting.
To manage annual weeds, mulch with straw, grass clippings, chopped leaves, or pine needles after the trenches have been filled in. Hand-hoeing while weeds are small is also effective.
These are very healthy asparagus ferns, a few weeks after harvest. Compost has been added and weeds have been killed by shallow hoeing.
The asparagus beetle is the most serious insect pest that affects asparagus. The larvae are dark and slug-like and are found on the ferns. There are two types of asparagus beetle; the common asparagus beetle (Crioceris asparigi) and the spotted asparagus beetle (C. duodecimpunctata). The adult spotted asparagus beetle is red with black spots, and the adult common asparagus beetle is metallic-colored with yellow spots. You can also reduce the damage caused by these insects if you practice “clean harvest”, meaning that you harvest all of the spears every time you harvest during the time that you’re harvesting, and then let all of them grow to ferns. At the end of fall, remove all of the dead ferns and crop debris that would otherwise shelter the adult beetles. If these practices do not control the pest, several insecticides are labeled for management of asparagus beetle.
Asparagus rust and Fusarium crown and root rot are common diseases. Both diseases can weaken asparagus plants, so that the planting becomes less productive over time. Most varieties are fairly resistant to rust. Removing old ferns provides additional protection. Fusarium is more difficult to control. Use vigorous varieties listed as tolerant and do not plant new asparagus in areas that were previously planted to asparagus.
Do not harvest asparagus until the third year after planting. The plants need at least two full seasons of growth before they build up ample food reserves to sustain harvests. In the third year, harvest only 2 to 3 weeks. In years thereafter, harvest no longer than 6 to 8 weeks (until about July 1 in southern New Hampshire). Harvesting for a longer period of time will not allow for maximum fern growth. Harvest the spears when they are 6 to 8 inches tall. Either snap or cut the spears off at ground level. To avoid injuring spears beneath the soil surface, do not cut more than one inch below the surface.
Asparagus is of highest quality when freshly harvested. It can be stored for a couple of weeks if the temperature is held at 34 degrees F and high relative humidity, but sweetness and flavor will deteriorate. Maintain short-term freshness by standing an asparagus bunch in about an inch of water in a flat-bottomed container in the refrigerator.
Asparagus should be cooled as quickly as possible and kept cool. The optimum temperature range is 32°F to 35.6°F. To cool asparagus, it can be dunked in or showered with cold water. The water should be of drinking water quality and, if used more than once, changed regularly and disinfected using an approved material (see the Safe Produce Indiana Resources page for an Excel tool listing sanitizers labeled for produce). The harvested spears remain alive and actively respiring until they are cooked or eaten. Respiration creates heat and burns up carbohydrates. Keeping the asparagus cool reduces the rate of respiration, which is essential for maintaining quality.
High relative humidity is also important for asparagus. The desired range is 95% to 100%. If asparagus will be stored in a cooler, it may be placed in plastic bags to maintain high humidity. The butt ends of spears should be kept moist. They may be set on a moist pad or in 1/2 inch of water.
Improper storage conditions can lead to poor quality asparagus. Spears held horizontally for a period of time will bend upwards at the tips; it is best to hold spears standing up. Asparagus quickly gets tough if kept above 50°F. It will also get tough if exposed to ethylene gas. Ethylene may be produced by the asparagus itself if it is bruised, broken, or diseased. Low humidity will result in shriveling and weight loss. Asparagus will freeze at temperatures below 31°F, becoming watersoaked and mushy when thawed.
Experienced asparagus producers probably have a good sense of how much the crop will grow under different weather conditions. For those with less experience, Table 3 may help guide decisions about when to harvest. Is it necessary to pick every day, or is it ok to skip a day? The warmer the weather, the faster the spears lengthen. The table shows how many inches a spear will grow each day, depending on its size and the average temperature. For example, with a high of 70 and a low of 50, the average temperature would be (70+50)/2=120/2=60°F. At an average temperature of 60°F, a 2-inch spear would grow 1.4 inches in one day, a 4-inch spear 2.0 inches, and a 6-inch spear 2.7 inches. After one day, the spears that started out at 6 inches would be ready to pick; after 2 days the 6-inch spears would be 11.4 inches, probably past the picking stage, and after two days the 4-inch spears would be 8 inches long and ready to pick.
ASPARAGUS, ASPARAGUS OFFICINALIS / LILIACEAE
Postharvest Atmosphere Management
AsparagusThe asparagus has a high rate of respiration, reason why it is essential to pre-cool it as soon as possible after its harvesting. This process can be carried out before or after packaging. The temperature must be put down to at least 4ºC, the nearest as possible to 0ºC. The methods used are water cooling, vacuum cooling and air cooling, although the best is the first one, since it allows to lower the temperature in 10-15 minutes.
When the turions are destined to far markets, it is recommended to dip the cut surface in a solution of calcium hypochlorite, thus controlling the bacterial infections.
The asparagus can only be stored for short periods of time; at best, the consumption must preferably take place within the week following the harvesting. If they are stored at temperatures between 0 and 2ºC with moisture levels around 100%, the turions may last up to 15-20 days. For longer storage it is recommended to raise the temperature to 2-3ºC, since temperatures near 0ºC may damage the produce if it is kept for too much time. Turions must not be stored together with species that produce ethylene, since this gas accelerates the hardening of the asparagus.
Whenever modified atmospheres are used, the asparagus may last for a month; in short storage, this method improves the quality of the produce. The conditions recommended are to maintain the levels of carbon dioxide at 10-14% for temperatures between 0 and 3ºC, or 5-9% for temperatures between 3 and 6ºC. Oxygen must not be modified. By means of these modifications there is a decrease of rots caused by fungi and bacteria.
If non-perforated plastic coverings are used, it is necessary to select the suitable time of exhibition, the type of plastic and atmosphere handling, otherwise there occur unsuitable environments for the turions storage.
During distribution, temperatures must be kept below 10ºC and the relative humidity must be high, specially if the produce is not protected with plastic. If they are placed on a humid surface they keep turgidity for a greater length of time. The produce that is spare or in reserve must be protected from the light, and it is better to dip the base in water.
The transport of asparagus must be carried out at temperatures between 0 and 5ºC, according to the length of the journey. In case of sea transport, the optimal temperature is 2.2ºC, 90 to 95% of moisture and levels of carbon dioxide around 5 and 10%.
The asparagus may undergo some modifications that reduce their quality during storage, such as the increase of fibreness, blight, bending, loss of taste and aroma and changes in their composition. They may also be affected by diverse microorganisms, like the bacterium Erwinia carotovora or the fungi Fusarium moniliforme, Penicillium hirsutum and Botrytis cinerea.
The asparagus has a high rate of respiration, so they can only be preserved for short periods of time, since there occur fast modifications that reduce their quality. They may also be subject to parasitic diseases.
Among the possible asparagus modifications we find the following ones.
The butt segment of asparagus contains numerous nutrients, including various antioxidants. In particular, fibers and several mineral contents are quite high. However, asparagus butt segment quality is reduced in processing. Therefore, research on the asparagus butt segment processing for development of food industry and for the benefit of economic is necessary. Water blanching is a pretreatment method applied in most fruit and vegetable industry today. Water blanching process can inhibit enzyme activity and reduce loss of food quality. However, water blanching can lead to loss of nutrient contents as well as changes in color and texture (sensory values). In this study, the temperature was investigated at 70°C, 75°C, 80°C, 85°C, and 90°C, and the blanching time was observed at 2, 4, 6, and 8 minutes. We evaluated the effect of blanching conditions through the percent retention of vitamin C, phenolic compounds, antioxidant capacity (DPPH assay), and changes of sensory values. The results show that blanching temperatures from 75°C to 85°C insignificantly affect quality of asparagus butt segment. However, nutrient contents and sensory values decrease rapidly with the increase of blanching time. When asparagus was blanched at 85°C for 4 minutes, the percent retention of vitamin C, phenolic and antioxidant capacity was 74.84% 80.34% and 71.24%, respectively. These results suggested the good blanching conditions for asparagus butt segment processing..
Increase of fibreness: it increases from the base upwards, diminishing the proportion of edible surface. This process is accelerated if the turions are exposed to ethylene.
Blight: it is caused by the loss of water, due to transpiration. It is shown in the loss of weight of the produce; there also occur longitudinal streaks. Sometimes the base of the asparagus is immersed in buckets of water, thus controlling the problem, although this method may lead to the development of bacteria. Another method used is the covering with plastic.
Bending and lengthening of the turions: the lengthening of the asparagus is greater at high temperatures. If the turions are kept in horizontal position and they receive direct sunlight, they will bend upwards, thus reducing their quality.
Loss of taste and aroma: the lower the temperatures are, the faster the process occurs.
The white asparagus may show a pink colouring if they are placed in direct sunlight right after their cutting or if they are not sufficiently cooled down.
During storage there also occur some changes in the composition of the asparagus. The levels of vitamin C and sugar decrease, whereas the acidity increases.
Among the parasitic diseases that may affect the asparagus we find the following:
Erwinia carotovora is a bacterium that produces a soft wet rot that gives off an unpleasant smell. The development of this disease takes place both in the base as in the apex of the turions. The white asparagus are more resistant than the green ones.
Fusarium moniliforme is a fungus that causes an initial necrosis on the tissue affected, which soon develops a pinky white coloured down. As the infection spreads, the area affected turns into a dark green colour and wet appearance.
Penicillium hirsutum is one of the fungi that affect mainly the postharvested asparagus. It attacks specially the area where the asparagus is cut, being the place where the fungus grows.
Botrytis cinerea is a fungus that causes a soft rot covered by a grayish-white down. The turions are infected in the field, mainly when the weather before the harvest is cold and rainy.