Blanching is a cooking process in which a food, usually a vegetable or fruit, is scalded in boiling water, removed after a brief timed interval, and finally plunged into iced water or placed under cold running water (known as shocking or refreshing) to halt the cooking process. Blanching foods helps reduce quality loss over time. [1] Blanching is often used as a treatment prior to freezing, dehydrating, or canning vegetables or fruits to deactivate enzymes, modify texture, remove the peel and wilt tissue. [2] The inactivation of enzymes preserves colour, flavour, and nutritional value. [2] The process has three stages: preheating, blanching, and cooling. [1] The most common blanching methods for vegetables/fruits are hot water and steam, while cooling is either done using cold water or cool air. [3] [4] Other benefits of blanching include removing pesticide residues and decreasing microbial load. [4] Drawbacks to the blanching process can include leaching of water-soluble and heat-sensitive nutrients and the production of effluent. [2]
Blanching is a process used in the home kitchen as well as used as a pre-treatment in the food industry. In both cases, its main purpose is to deactivate enzymes that cause browning as well as textural changes and off-flavors. [2] Enzymes that cause deterioration in fruits and vegetables include lipoxygenase, polyphenoloxidase, polygalacturonase, and chlorophyllase. [5] Catalase and peroxidase are commonly used to determine blanching success, since they are the most thermal-resistant enzymes of concern. [2] [3] These enzymes are responsible for the loss of flavor, color, texture, and nutritional qualities during product storage. [4] [6]
The blanching process expels air trapped inside plant tissues, which is a vital step before canning. [4] Blanching prevents the expansion of air during processing, which reduces strain on the containers and the risk of cans having faulty seams. [4] Moreover, removing gas from foods like pears results in better texture and reduces oxidation of the product. [4] Also, the intercellular gases removed results in better color retention. [7]
Fruit, vegetable, and nut peeling is also important in food processing. [4] When almonds or pistachios are blanched, the skin of the nut (botanically the seed coat surrounding the embryo) softens and can be easily removed later. Steam peeling produces less environmental pollution and peeling losses, as compared to chemical or manual peeling processes. [4]
Other uses of blanching are enhancing drying rate and product quality, decreasing microbial load, removing pesticide and toxic residues, increasing extraction of bioactive compounds, surface cleaning, removing damaged seeds or foreign materials, killing parasites and their eggs, and reducing oil uptake. [4]
Traditionally, blanching is done using either a water bath or saturated steam. [5] In both methods, the food is heated for a short period of time and then introduced into either cold water or cold air to quickly stop the heating process. At the industrial level, foods move on a continuous conveyor belt through preheating, holding, and cooling. [4]
For hot water blanching, vegetables are immersed under pre-warmed water (70 to 100 °C) for varying amounts of time, depending on type and quantity. [4] When the product is heated by water, greater uniformity of heating is achieved, especially when compared to hot air. This advantage allows hot water blanching at lower temperatures, but requires longer blanching times. [2] Water is heated and cooled using heat exchangers and recirculated for continuous use, reducing costs. [3]
Steam blanching systems inject hot air (~100 °C) onto food as it passes through the blanching system on a conveyor belt. [2] This method greatly reduces the leaching of water-soluble compounds from the product and is the preferred technique for smaller foods and those with cut surfaces. [2] [3] Steam blanching is more energy-efficient, and the ability for quick heating allows for shorter processing times. This reduced heat exposure preserves color, flavor, and overall quality of the food; however, evaporation may occur leading to lower masses and product yields. [3]
Directly following the heat treatment, vegetables/fruits are quickly chilled by cold water. [2] A common alternative to cooling with cold water is cooling with cold air. This method of cooling prevents the leaching of water-soluble nutrients; however, the air causes evaporation and lowers the mass of the vegetable—a monetary disadvantage for industry. [3]
Emerging technologies include ohmic, infrared, microwave, and radio frequency blanching. [4]
It is important to consider the recommended times and temperatures for a food product when blanching. Times and temperatures are based on the type of food, size, shape, and other factors. [3] Over-blanching can lead to an excessive loss of nutrients and aromatic compounds, as well as softening of the food. [3] Blanching at temperatures or times lower than those recommended may not effectively inactivate all enzymes. In addition, this may also cause the release of more enzymes from the plant tissue, causing greater overall enzymatic activity and faster spoiling of the product. [3]
Although blanching is a thermal process, the times and temperatures are not sufficient to effectively destroy all microorganisms. [3] Blanching is often seen as a pre-process to later preservation steps. For example, blanching in the home is often done in combination with freezing; blanching in industry is also utilized before canning, dehydration, or heat sterilization. [3] [8]
A limitation to hot water blanching is the leaching of water-soluble nutrients and the degradation of thermal sensitive compounds. [4] Vitamins, minerals, and other water-soluble compounds, such as proteins, sugars, and flavor compounds, diffuse out of the food and into the water, lowering the overall quality of the food. [4] The degree to which compounds diffuse out of food depends on the food's composition and characteristics, the water to food ratio, the blanching temperature, and other variables. [3] Ascorbic acid, thiamin, and many aromatic compounds are heat-sensitive.[ citation needed ]
A complication in the food industry is the production of effluent from water blanching systems. [2] Blanching with reused water can lead to a buildup of water-soluble compounds that are considered pollutants, and therefore must be properly treated before being discharged. [4] This can increase capital costs at the industrial level and has been a main reason for the development of newer blanching technologies. [3] [4]
Cooking, also known as cookery or professionally as the culinary arts, is the art, science and craft of using heat to make food more palatable, digestible, nutritious, or safe. Cooking techniques and ingredients vary widely, from grilling food over an open fire, to using electric stoves, to baking in various types of ovens, reflecting local conditions. Cooking is an aspect of all human societies and a cultural universal.
In the field of food processing, pasteurization is a process of food preservation in which packaged and unpacked foods are treated with mild heat, usually to less than 100 °C (212 °F), to eliminate pathogens and extend shelf life. Pasteurization either destroys or deactivates microorganisms and enzymes that contribute to food spoilage or the risk of disease, including vegetative bacteria, but most bacterial spores survive the process.
Orange juice is a liquid extract of the orange tree fruit, produced by squeezing or reaming oranges. It comes in several different varieties, including blood orange, navel oranges, valencia orange, clementine, and tangerine. As well as variations in oranges used, some varieties include differing amounts of juice vesicles, known as "pulp" in American English, and "(juicy) bits" in British English. These vesicles contain the juice of the orange and can be left in or removed during the manufacturing process. How juicy these vesicles are depend upon many factors, such as species, variety, and season. In American English, the beverage name is often abbreviated as "OJ".
Pressure cooking is the process of cooking food with the use of high pressure steam and water or a water-based liquid, inside a sealed vessel called a pressure cooker; the high pressure limits boiling and creates higher temperatures not possible at lower pressures which allow food to be cooked much faster than at normal pressure.
Peanut butter is a food paste or spread made from ground, dry-roasted peanuts. It commonly contains additional ingredients that modify the taste or texture, such as salt, sweeteners, or emulsifiers. Consumed in many countries, it is the most commonly used of the nut butters, a group that also includes cashew butter and almond butter.
Tempeh or tempe is a traditional Indonesian food made from fermented soybeans. It is made by a natural culturing and controlled fermentation process that binds soybeans into a cake form. A fungus, Rhizopus oligosporus or Rhizopus oryzae, is used in the fermentation process and is also known as tempeh starter.
Freezing food preserves it from the time it is prepared to the time it is eaten. Since early times, farmers, fishermen, and trappers have preserved grains and produce in unheated buildings during the winter season. Freezing food slows decomposition by turning residual moisture into ice, inhibiting the growth of most bacterial species. In the food commodity industry, there are two processes: mechanical and cryogenic. The freezing kinetics is important to preserve the food quality and texture. Quicker freezing generates smaller ice crystals and maintains cellular structure. Cryogenic freezing is the quickest freezing technology available due to the ultra low liquid nitrogen temperature −196 °C (−320 °F).
A slow cooker, also known as a crock-pot, is a countertop electrical cooking appliance used to simmer at a lower temperature than other cooking methods, such as baking, boiling, and frying. This facilitates unattended cooking for many hours of dishes that would otherwise be boiled: pot roast, soups, stews and other dishes.
Browning is the process of food turning brown due to the chemical reactions that take place within. The process of browning is one of the chemical reactions that take place in food chemistry and represents an interesting research topic regarding health, nutrition, and food technology. Though there are many different ways food chemically changes over time, browning in particular falls into two main categories: enzymatic versus non-enzymatic browning processes.
Freeze drying, also known as lyophilization or cryodesiccation, is a low temperature dehydration process that involves freezing the product and lowering pressure, thereby removing the ice by sublimation. This is in contrast to dehydration by most conventional methods that evaporate water using heat.
Sous vide, also known as low-temperature, long-time (LTLT) cooking, is a method of cooking invented by the French chef Georges Pralus in 1974, in which food is placed in a plastic pouch or a glass jar and cooked in a water bath for longer than usual cooking times at a precisely regulated temperature.
Thermal pollution, sometimes called "thermal enrichment", is the degradation of water quality by any process that changes ambient water temperature. Thermal pollution is the rise or drop in the temperature of a natural body of water caused by human influence. Thermal pollution, unlike chemical pollution, results in a change in the physical properties of water. A common cause of thermal pollution is the use of water as a coolant by power plants and industrial manufacturers. Urban runoff—stormwater discharged to surface waters from rooftops, roads, and parking lots—and reservoirs can also be a source of thermal pollution. Thermal pollution can also be caused by the release of very cold water from the base of reservoirs into warmer rivers.
Drying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. This process is often used as a final production step before selling or packaging products. To be considered "dried", the final product must be solid, in the form of a continuous sheet, long pieces, particles or powder. A source of heat and an agent to remove the vapor produced by the process are often involved. In bioproducts like food, grains, and pharmaceuticals like vaccines, the solvent to be removed is almost invariably water. Desiccation may be synonymous with drying or considered an extreme form of drying.
The following outline is provided as an overview of and topical guide to the preparation of food:
Tomato soup is a soup with tomatoes as the primary ingredient. It can be served hot or cold, and may be made in a variety of ways. It may be smooth in texture, and there are also recipes that include chunks of tomato, cream, chicken or vegetable stock, vermicelli, chunks of other vegetables and meatballs. Many companies have their own versions of tomato soup which all vary in taste, portions and ingredients.
An evaporator is a type of heat exchanger device that facilitates evaporation by utilizing conductive and convective heat transfer, which provides the necessary thermal energy for phase transition from liquid to vapor. Within evaporators, a circulating liquid is exposed to an atmospheric or reduced pressure environment, causing it to boil at a lower temperature compared to normal atmospheric boiling.
Aseptic processing is a processing technique wherein commercially thermally sterilized liquid products are packaged into previously sterilized containers under sterile conditions to produce shelf-stable products that do not need refrigeration. Aseptic processing has almost completely replaced in-container sterilization of liquid foods, including milk, fruit juices and concentrates, cream, yogurt, salad dressing, liquid egg, and ice cream mix. There has been an increasing popularity for foods that contain small discrete particles, such as cottage cheese, baby foods, tomato products, fruit and vegetables, soups, and rice desserts.
Instant rice is a white rice that is partly precooked and then is dehydrated and packed in a dried form similar in appearance to that of regular white rice. That process allows the product to be later cooked as if it were normal rice but with a typical cooking time of 5 minutes, not the 20–30 minutes needed by white rice. This process was invented by Ataullah K. Ozai‐Durrani in 1939 and mass-marketed by General Foods starting in 1946 as Minute Rice, which is still made.
A climbing/falling film plate evaporator is a specialized type of evaporator in which a thin film of liquid is passed over a rising and falling plate to allow the evaporation process to occur. It is an extension of the falling film evaporator, and has application in any field where the liquid to be evaporated cannot withstand extended exposure to high temperatures, such as the concentration of fruit juices.
Instant tea is a powdered mix in which water is added, in order to reconstitute it into a cup of tea. The earliest form of instant tea was developed in the United Kingdom in 1885. A patent was granted for a paste made of concentrated tea extract, sugar, and evaporated milk, which became tea when hot water was added. However, no notable developments were made until spray drying technology allowed for drying the tea concentrates at a temperature which did not damage the flavors of the product.