Rotary & Auger Blanchers
VOL. 19 NO. 9
Rotary and auger blanchers are commonly used for water blanching vegetables. Both are relatively economical, effective for most products and have good control of product flow. A rotary blancher consists of a reel, which is an auger wrapped with a perforated skin, rotating in a tank of water. An infeed chute drops the product into the reel. Paddles, fastened to the skin and reel end at the discharge, lift the product out of the water and transfer it to the discharge chute. Rotary blanchers have always performed well for free flowing product. Newer designs, utilizing trunions outside the tank on each end to support the reel, are effective for harder to handle products, such as whole green beans. Most rotary blanchers operate with the bottom third of the reel immersed. If the product sinks, a center tube design utilizing bearings at each end to support the reel, makes it possible to operate with the bottom half of the reel immersed, providing considerably higher capacity. Rotary blanchers predominated in the 1940's and 1950's.
During the 1960's, auger blanchers started becoming more prevalent. An auger blancher looks like a large diameter screw conveyor. On most units for french fry potatoes, a large wheel with paddles catches the product discharging from bottom of the trough and elevates it to the discharge chute. This component, aptly named Ferris wheel, has an inside diameter slightly larger than the auger diameter, allowing the discharge chute and water level to be located near the top of the auger. For the same size unit, a Ferris wheel auger blancher has considerably larger capacity than a rotary blancher. There is, however, a trade off. With fragile product, an auger blancher should operate under half full to avoid unacceptable breakage. Another discharge option is a single paddle side discharge. While this configuration limits water level and product volume to the bottom half of the auger, it is very effective for green vegetables. In the early 1970's, Gem manufactured several side paddle discharge units for spinach. Since blanch time for spinach is about one minute the auger was rotating fast enough to pump all the water out of the blancher every minute. A dewatering belt separated the product from the water, which was continually pumped back to the infeed end of the blancher. One discharge method that fell out of favor, and now appears to be making a come back, utilizes a hydropump to convey product from the bottom of the trough at the discharge end to a dewatering device located at an elevation above the top of the auger.
Direct steam injection is the normal method of heating water for both auger and rotary blanchers. Early auger blanchers used several steam injectors located along the bottom of the trough. Each one fed with a line from the steam distribution header. A more economical solution was a full-length steam chamber underneath the bottom of the auger trough. Punch plate was used for the common surface between the steam chamber and the auger trough. Rotary blanchers used either two full-length steam distribution pipes, or shallow tank steam injection nozzles. External heating is an alternative to direct steam injection. Water is recirculated outside the blancher utilizing either a nozzle to inject steam into the recirculating water or a heat exchanger to provide heat for the blancher. If you need a blancher, contact Gem. We can help select the right blancher for your application.