Harvesting and processing technology of macadamia nuts
1、 Harvesting of macadamia nuts
1. Harvesting period
The timely harvesting period of macadamia nuts is a very important production technology link. Premature harvesting of macadamia nuts can result in plump kernels, low kernel yield, difficult peel peeling, and poor storage tolerance; If harvested too late, the fruit will stay on the ground for too long, which will increase the chance of being infected by mold and lead to a decrease in fruit quality. Harvesting should be done on sunny days (rainy or rainy days are not suitable for harvesting) to improve the quality and storage of fruits.
The ripening period of summer magnolia fruit is generally from mid August to mid October. Due to the flowering period of more than a month, the ripening time of the fruit is inconsistent, and it needs to be harvested first. After the fruit matures, the skin will change from brown to dark brown, the shell is hard, and the skin is easy to peel off. At this time, the seed kernels are full, white or milky white, and the flavor is fragrant. It is the best time to harvest the fruit.
2. Harvesting methods
The harvesting of macadamia nuts generally involves manual harvesting and mechanical vibration harvesting. When the fruit is ripe, it is advisable to use fruit hooks to peel off the involucre one by one. Using other methods to drop ripe fruits can easily damage the branches and leaves of the fruit tree, affecting the yield of the following year; Using mechanical harvesting: Two weeks before harvesting, spray 500 times the liquid ethephon on the fruit tree to accelerate ripening, and then use appropriate mechanical vibration on the branches to make the ripe fruit fall. Using ethephon can cause early leaf detachment and to some extent affect the growth of the fruit tree.
2、 Processing of macadamia nuts
Nut with clip → Fruit removal clip → Grading of fruit with shell → Drying treatment of fruit with shell → Storage → Breaking of shell → Grading of kernel → Packaging.
1. Orchard collection with fruit shells
Macadamia nuts have different ripening times due to different varieties, and the fruits will gradually fall to the ground during ripening. They should be collected every 2-3 days after the fruits fall. After the fruits are collected, the mixed stones, empty fruits, fallen leaves, and other debris should be cleaned and transported to the processing plant for further processing.
2. Fruit stripping clip
The moisture content of the newly harvested ripe nut fruit clip is about 35-45%, and the moisture content of the nut kernel is about 23-25%. The clip should be removed within 24 hours. If the clip cannot be removed within 24 hours, the fruit clip must be placed in a ventilated and dry place to air, but cannot be directly exposed to sunlight. If the fruit clip is stacked together, the nut is prone to fermentation and spoilage under high temperature and humidity, which affects its quality.
(1) Artificial peeling method: Use rubber as a pad to fix the nut, and then use a hammer to separate the peel. This method is suitable for small-scale plantations, with the advantage that the peel is easy to peel and does not cause much damage to the shell. High quality kernel yield can be guaranteed.
(2) Mechanical pod removal method: A double screw pod removal machine is used to separate the fruit peel under the action of mechanical friction and pressure. The advantage of this method is that the green peel is easy to detach, with high work efficiency, and is suitable for large plantations. When using this method, the spring pressure should be adjusted to the optimal position, so as not to damage the fruit shell as much as possible and avoid affecting the quality of the fruit kernel after the shell ruptures.
3. Screening and grading of shelled fruits
Fruit with shell is classified using a sieve or multi-stage rotary drum classifier: the diameter of the first grade fruit is ≥ 27mm, the diameter of the second grade fruit is 27mm>D ≥ 24, and the diameter of the third grade fruit is 24mm>D ≥ 18. The surface of the fruit shell is required to be smooth and clean, and the total amount of incomplete fruit should not exceed 4%.
4. Drying treatment of shelled fruits
After removing the pods of macadamia nuts, the moisture content of the kernels is 23% to 25%, so it is necessary to dry them in a timely manner. The correct drying process and time are necessary to obtain durable shell fruits and high-quality kernels.
(1) Natural air drying: Spread and air graded nuts on a steel wire air drying rack, with a thickness of no more than 20cm. Turn and air several times a day. After about a week, shake the nuts to hear the sound of the kernels hitting inside the seed shell. The moisture content of the kernels is about 10%, which can be used for short-term storage and sales.
(2) Artificial drying: Areas with high nut production should be centrally processed to accelerate drying speed and achieve the required moisture content. At present, there are two types of drying devices used in shell fruit processing plants, which are based on the principle of placing nuts into a drying oven or warehouse and drying them through manual air blowing and heating. In order to ensure the quality of the kernels and extend the storage time of the peeled fruits, the drying temperature of the peeled fruits should be carried out as follows: spreading (2-3 days) → room temperature (2-3 days) → 38 ℃ (1-2 days) → 44 ℃ (1-2 days) → 50 ℃ (dried to the required moisture content).
5. Storage with shell fruit
Shelled fruits are generally stored indoors and at low temperatures. During storage, it is important to avoid the shell from suddenly falling from a height, as severe collisions can damage the kernels. When the moisture content of the shell fruit is below 10%, the allowable height for falling is 2 meters.
(1) Ordinary indoor storage method: Put dried shelled fruits into jute bags and store them in a ventilated and dry place with backlight. The stacking of fruit strips should leave a passage at a distance of 25-30 cm from the warehouse wall; To avoid dampness, a moisture-proof layer of 10 cm or more should be installed on the ground.
(2) Low temperature storage method: Dry the fruit with shell until the moisture content of the kernel is less than 5%, pack it in gunny or plastic bags, and store it in a low-temperature cold storage at 0-4 ℃ to prevent rancidity caused by oil oxidation. The storage period can be more than one year.
6. Broken shell fruit (kernel extraction)
Breaking the shell to extract kernels is a very important process in macadamia nut processing technology, and the water content of the kernels before breaking the shell is generally controlled at 2% to 5%. Usually, manual or mechanical methods are used to separate the kernel and shell of the fruit.
(1) Manual method: Use a handle and rocker pressure type semi continuous shell breaking machine. When pressing the fruit, pay attention to placing the abdominal suture perpendicular to the blade surface, and apply even force. Do not press hard or repeatedly, otherwise it will affect the integrity of the fruit kernel and reduce its commercial value.
(2) Mechanical method: Its working principle is to use a fixed knife and a rotating knife to clamp the fruit shell back and forth in a certain cavity, causing the shell and kernel to separate. Then, it is screened, selected, and then floated with clean water, further dried to a moisture content below 1.5% before being suitable for storage or future baking.
7. Kernel grading
The kernels are divided into three levels: the dried kernels are placed in clean water for flotation, and the oil content of the kernels is ≥ 72%. The kernels that float in water with a density of 1.00 kg/L are classified as first level kernels, characterized by plump, light colored, smooth base, bright brown yellow color after roasting, crisp texture, and soft nut aroma; The oil content of fruit kernels is 66% -72%, and they will sink in water. They should be bleached in salt water with a density of 1.025 kg/L, characterized by slightly shrinkage and black color of roasted dried fruit kernels. The processing quality is unstable, and there is a tendency to go bad, with a soft texture; The remaining three grade kernels have an oil content of 50% -66%, characterized by small and black roasted kernels, which are hard or rough in texture, and appear dark brown after processing. The kernels are hard and have a burnt taste. The graded kernels need to be further dried to a moisture content of about 1.5% before they can be stored or further processed.
(1) Packaging with shell fruit
It should be packaged in sturdy, dry, clean, odorless jute bags or non-toxic plastic bags, with a net weight of 50 kg per bag. After bagging, it should be immediately sealed and marked with weight, grade, manufacturer, etc.
(2) Nut packaging
The outer packaging material of fruit kernels must be made of sturdy, dry, clean, and odorless cardboard boxes, lined with non-toxic tin foil plastic bags, and filled with small bags of antioxidants, while also playing a drying role. Mass sales of nuts usually use vacuum packaging, while shelf sales usually use nitrogen filled packaging. After packing, it should be immediately sealed and tied tightly, and the weight, grade, manufacturer, etc. should be indicated.