Wasabi is an elite Japanese delicacy also known as Japanese horseradish. It is a perennial herb commonly used for flavouring food. Wasabi harvesting is aimed at reaping high quality rhizomes which are then exported world over for profit generation. Harvesting wasabi should be done with precision in order to maintain the quality and quantity of the yield. Wasabi is vulnerable to pest and disease infestation during harvesting. As such, if done by inexperienced personnel, farmers risk losing a significant amount of yield.

Harvesting Time

This is regarded as one of the most important aspects in harvesting wasabi. Farmers should take note that the actual time of harvesting wasabi has a direct correlation to the quality of the rhizome. It is therefore advisable to conduct frequent checks so as to identify the most desirable time to harvest. The recommended period for harvesting wasabi is generally when the out layer of stems is green; very dark or very light coloured stems are considered unsuitable which translates to lower price. It takes at least 2 years for wasabi to mature to its full size and flavour, however, farmers usually leave it for up to 3 years before harvesting. Wasabi can be harvested throughout the year depending on climate and seed variety. The introduction of greenhouses with controlled environments, improved seed varieties and fertilisers have fastened the harvest period to about 8 weeks. The plant normally reaches the peak stage of growth in its early second year hence the most ideal time for harvesting wasabi. Also, it should be harvested early in the morning when temperatures are cool.

Wasabi is vulnerable to pest and disease infestation during harvesting thus has a habit of developing defects when left unattended in high temperatures. In addition, phenolic compound accumulation during harvesting causes the vascular tissue of the wasabi to turn blue-black thus affecting quality. In severe cases, this happens in 24hours to 48 hours spreading to all parenchyma tissues resulting in the discoloration of the roots in just about 3 days. Most farmers therefore harvest wasabi earlier to minimise loss due to discolouration. As such, it is of outmost importance for wasabi harvesting to be done within the recommended time-frame in order to avoid losses and to acquire a high quality yield.

Harvest Maturity

At harvest, the rhizome should be cylindrical in shape, slightly curved, covered with leaf scars, and pointed at the terminal bud. Another indicator for a fully matured wasabi are the evergreen leaves which should be about  25cm in diametre upon reaching maturiy. Petioles can extend up to 50 cm in height on a mature plant. A fully seasoned wasabi rhizome can grow to an estimated size of 5cm to 15cm in length, 2cm to 5cm in diameter. The largest stems weigh 60 to 150g at maturity level.

Harvesting Method

Wasabi harvesting is done manually (harvesting by hand). The plant is pulled up by hand and offshoots are removed. Care should be taken to avoid damage as they are later used for planting new crops. After cutting off roots and leaves, the rhizome is washed to remove dirt. The removed offshoots can be planted immediately if they are healthy and strong enough. In fact, planting wasabi is usually done on the day of harvest provided temperatures are cool and there is high moisture (8oC to 18oC temp). Wasabi harvesting should be done by people with good hygiene and gloves have to be worn at all times to avoid damage and contamination which causes infestation thereby diminishing the quality of the yield.

Trimming and Cleaning

Trimming and cleaning is an important part of harvesting wasabi as they play big role in its presentation. Wasabi stems should be trimmed to a reasonable size. Excessive trimming indicates defect or discolouration which is considered as undesirable. When trimming, the roots should be removed leaving the base of the tem intact. Petioles are trimmed to approximately 1/3 the length of the stem. Proper wasabi harvesting demands that stems are cleaned with cool water and a soft brush under high pressure. Care must be taken to avoid damaging the soft petiole tissue hence the need for experienced harvesting personnel.

Grading

Harvesting wasabi typically involves picking stems in different stages of maturity. A single wasabi farm produces rhizomes of different sizes and quality. For this reason, wasabi is graded into different categories, namely: size and quality. Premium quality stems are separated from standard of defected wasabi. The same is applied to wasabi of different sizes. Grading allows farmers to price produce accurately and fairly.

Storage

Another important aspect of harvesting wasabi is storage. Storage determines the shelf life of the produce. Wasabi rhizomes should be packed and stored soon after harvesting for a prolonged shelf life. They have to be kept moist and chilled at 4oC in storage. Chilled polystyrene boxes are used for packaging stems prior to storage. The rhizomes are then stored in cold storage units where they retain freshness for up to 30 days. In the absence of cold storage units, the stems can be dried and ground.

Wasabi Yield

Successful production and harvesting of wasabi is characterised by a yield of approximately 10 tonnes per hectare (semi-commercial farms). A healthy individual plant produces about 4 to 14 wasabi stems. This however differs with varying climatic conditions, soil or water fertility and seed variety among other factors. Some areas with improved agricultural technologies record yields of up to double this amount or more. Note that although overall yields are high, most farmers record much lower yields of the required premium quality. In a yield of 10 tonnes per hectare, only 4 tonnes can be of the ideal quality. Good quality wasabi is evenly tapered; uneven tapering is an undesirable sign which lessens its cost thus affecting profit margins.

 

Similar to most agricultural produce, greatest production losses occur during the process of harvesting. Poor handling when harvesting wasabi leads to diminished quality and infestation which often spreads quickly possibly affecting the entire harvest. Therefore, the need to acquire relevant knowledge and to develop skills for proper wasabi harvesting can never be exaggerated. The general quality, quantity and profitability of this agricultural venture relies heavily on harvesting of wasabi.