Jerusalem Artichoke Association of Canada
Harvesting and Storing Jerusalem artichokes
Fertility programs similar to that of potatoes are often used as a starting point for Jerusalem artichokes. Yields are relatively high, typically 16-20 t/ha for tubers and 18-28 t/ha green weight for foliage. The yield of tubers and tops depends on the variety of the plant and the time of harvest.
Tubers are harvested in late fall, usually after the first frost followed by cold storage. Harvest can also be accomplished throughout winter. In this case, tubers are field stored and harvested as needed.Tubers can be harvested using potato harvesting machinery. Harvesting the Jerusalem artichoke tubers is in fact similar to potatoes with a few exceptions. Compared to the weak potato vines that age before harvest, Jerusalem artichoke plants continue to grow and bare strong stems. While potato tubers are easily separated from the stems, a large mass of Jerusalem artichoke tubers are strongly attached and intertwined with the roots. Farmers often use smaller chains on the potato digger and increase the agitation – this helps decrease a potential 50% loss that may occur with a traditional potato digger. The tubers need to be handled carefully after harvesting to prevent bruising. Tops, roots and tubers can usually sorted as they are harvested or dried and then sorted. Jerusalem artichokes will wilt and soften much faster than potatoes and cannot be left at a low humidity for a long period of time before storage. Jerusalem artichokes tubers are usually harvested in the fall or left in the ground for the winter storage and harvested in the spring. The recommended storage conditions are 0-2°C at a relatively humidity of 95% for 4-5 months. The tubers tend to spoil more easily when diseased, bruised or skinned. Tubers kept for seeding are not recommended to be frozen.
Tubers are either stored in a refrigerated storage, common storage in root cellars or in situ field storage. In the first two cases, tubers are harvested in fall and placed in storage. With field storage the tubers are left in the ground and harvested as needed. Refrigerated storage is routinely used for seed and fresh market tubers, particularly in situations where field storage is not possible. Cold storage is highly effective but costly. Field storage is a viable option in the northern hemisphere whre cold temperatures prevail throughout winter. This is why sandy, well-drained soils are preferred since they allow harvest during the whole winter.
When stored, the carbohydrates in the tubers undergo important alterations. Although, inulin is referred to as one compound, it is in fact a series of molecules that vary in chain length, these begin to depolymerize during storage whether harvested or left in the ground. As the chain length decreased the ability of inulin to mimic a lipid diminishes. With progressive depolymerization, the ratio of fructose to glucose is also decreased and less fructose is obtained upon inulin hydrolysis. For instance, during the winter storage the ratio of fructose to glucose is decreased. Some studies observes a decreased in the conversion of fructose to glucose in the ratio of 11-12 These changes are important factors to take into consideration when inulin from Jerusalem artichokes is used as fat replacement or high fructose syrups. For the production of alcohol, decreased polymerization is beneficial since the first hydrolysis step is not necessary. Numerous factors affect the rate of depolymerization of inulin. The rate of hydrolysis is dependent on the degree of polymerization of inulin, increasing in rate as the length increases to a degree of polymerization of 8. The rate of hydrolysis does not appear to be affected by the fructose concentration. Another factor is the storage temperature, the rate of hydrolyses in impaired when tubers are stored at 2°C compared to 5°C. For instance, when the tubers are left in the ground in the Canadian winter, the total reducing sugar, sucrose, is reduced when the tubers are harvested in spring. The fructose concentration does not appear to change.