Blanching in vegetable production
Blanching is a short time thermal process very important to prepare the vegetal raw material. Generally consist of expose the entire product to high temperatures (70-100ºC) for a short period of time. The primary function of this operation is:
- to inactivate or retard bacterial and enzyme action, which could otherwise cause rapid degeneration of quality.
- the expelling of air and gases in the product,
- to soften the product
- to reduce the microbial load
- in some cases, to fix the colour.
Before blanching, the food is preheated. Blanching may be accomplished by direct or indirect heating systems. This may depend on the product. Direct heating is normally made by immersion into hot water, at 80 to 100 °C, or by exposure to live steam. The operation is normally carried out in horizontal chambers. The residence time in the blancher can vary from approximately 1 to 5 minutes depending on the fruit or vegetable being blanched. For some products, direct contact with water is to be avoided so heat-exchangers working with hot water or vapour are applied (European Commission, 2006).
After blanching, the food has to be cooled immediately, using either water or air, to prevent excess of heating.
Blanching is an important step in the processing of fruit and green vegetables.
- Blanching is a high energy demanding operation within the process of fruits and vegetables. Energy consumption in blanching can be 30-40 % of total energy consumed in the process.
- The main blanching technologies are: hot water blanching and steam blanching, both working in a range of temperature near 100º C.
- Blanching is used in most vegetables destined for canning, freezing or drying. Typically, it is carried out using hot water or steam. If the produce is to be frozen, blanching is followed by water or air cooling. Energy consumption depends on, not only the type of blanching device, but also the type of subsequent cooling step.
- In terms of energy consumption, the belt blancher with water cooling has the lowest total consumption. The heat released by the cooling of the product in the cooling zone is used to preheat the vegetables. In this way, less steam is necessary for blanching.
- The electricity consumption of the belt blancher with air cooling, which produces 7 to 30 kWhe/t of frozen product, is significantly higher than that of the belt blancher with water cooling, which produces 2 to 9 kWhe/t of frozen product, or the drum blancher with counter current water cooling, which produces 1 to 2.6 kWhe/t of frozen product (European Commission, 2006)
|Friuts- Vegetables- Herbs||Temperature [°C]||Pressure (bar)||pH||Residence Time [min]||Details||Literature|
|Beans||100||9-10||4||Schuchmann, H., Schuchmann, H. P.: Lebensmittelverfahrenstechnik|
Additional information on the process
Case studies: Gangl/Austria
- European Commission, 2006. BREF Reference document on Best AvailableTechniques in the Food, Drink and Milk industries.
- AINIA- Guía tecnológica: La industria de elaborados vegetales. Available at: < http://www.prtr-es.es/Data/images//La%20industria%20de%20elaborados%20vegetales-AB08EBAE53A6F06F.pdf>
- MAPA. 2006. Guía de Mejores Técnicas Disponibles en España del Sector de los Transformados Vegetales. Available at http://www.prtr-es.es/Data/images//Gu%C3%ADa%20MTD%20en%20Espa%C3%B1a%20Transformados%20Vegetales-1F078444C914B509.pdf