3 100% Effective Ways to Completely Erase a Hard Drive

How to Completely Erase a Hard Drive

Several ways to completely erase a hard drive of all data

If you want to completely erase a hard drive, it’s not as easy as deleting everything on it. To truly erase hard drive data forever, you’ll have to take some extra steps.

When you format a hard drive you don’t actually erase the hard drive of data, you only erase the location information for the data, making it «lost» to the operating system. Since the operating system can’t see the data, the drive looks empty when you look at its contents.

However, all the data is still there and, unless you truly erase the hard drive, can be recovered using plan software or hardware.

The most responsible thing you can do before recycling a hard drive, or even disposing of one, is to completely erase the hard drive. If you don’t erase the hard drive, you risk exposing sensitive personal data that you previously deleted—data like social security numbers, account numbers, passwords, etc.

According to most governments and standards organizations, there are only three effective methods of erasing a hard drive, the best of which depends on your budget and future plans for the hard drive:

Wipe the Hard Drive Using Free Data Destruction Software

Free for anyone to download and use.

The hard drive is still usable afterward.

Must have at least a little knowledge on how to use this type of software.

Not the MOST secure method since the drive is still usable.

By far, the easiest way to completely erase a hard drive is to use free data destruction software, sometimes called hard drive eraser software or disk wipe software.

Regardless of what you call it, a data destruction program is a piece of software designed to overwrite a hard drive so many times, and in a certain way, as to make the ability to extract information from the drive nearly impossible.

Some more stringent hard drive erasing standards forbid using data destruction software, probably because of the possibility of user error and the variety of software and methods that exist. However, as long as your drive doesn’t contain national security information, you should feel very comfortable using any one of these programs to erase a hard drive.

You must erase a hard drive using this method if you, or someone else, ever plan on using the drive again. The next two ways to erase a hard drive will make the drive unusable. For example, you should erase a hard drive this way if you’re selling or giving the drive away.

Use a Degausser to Erase the Hard Drive

Garner Products, Inc.

Really secure since it completely destroys it from being used again.

Usually isn’t a free-to-use method for erasing a hard drive.

Another way to permanently erase a hard drive is to use a degausser to disrupt the magnetic domains on the drive—the very way that a hard drive stores data.

Some NSA approved automatic degaussers can erase dozens of hard drives in an hour and cost tens of thousands of US dollars. NSA approved degaussing wands, used to manually degauss a hard drive, can be purchased for around $500.


Degaussing a modern hard drive will also erase the drive’s firmware, rendering the drive completely useless. If you want to erase a hard drive, but also want it to work properly after being erased, you must erase the drive using data destruction software (option 1, above) instead.

For the average computer owner or organization, degaussing probably isn’t a cost-effective way to completely erase a hard drive. In most cases, physically destroying the drive (below) is the best solution if the drive isn’t needed anymore.

Physically Destroy the Hard Drive

Jon Ross / Flickr / CC BY 2.0

Leaves no way to recover the data.

You can do it yourself for free.

Could be dangerous without professional help.

Physically destroying a hard drive is the only way to absolutely and forever ensure that the data on it is no longer available. Just as there is no way to extract the written information from a burned piece of paper, there is no way to read the data from a hard drive that is no longer a hard drive.

According to the National Institute of Standards and Technology Special Publication 800-88 Rev. 1 [PDF], destroying a hard drive makes recovery «infeasible using state of the art laboratory techniques and results in the subsequent inability to use the media for storage of data.» Most of the standards that exist to erase a hard drive mention several ways to physically destroy one including disintegration, grinding, pulverization, incineration, melting and shredding.

You can destroy a hard drive yourself by nailing or drilling through it several times, making sure the hard drive platter is being penetrated each time. In fact, any method of destroying the hard drive platter is sufficient including sanding the platter after being removed or shattering it (as shown here).


Wear safety goggles and take great caution ​when destroying a hard drive yourself. NEVER burn a hard drive, put a hard drive in a microwave, or pour acid on a hard drive.

If you’d rather not destroy your hard drive yourself, several companies offer the service for a fee. A few services will even fire a round of bullets through your hard drive and send you the video!


Vegetable midges: simple and effective methods of destruction

Industrialized nations are grappling with the problem of expeditious and safe waste disposal. Non-biodegradable and toxic wastes like radioactive remnants can potentially cause irreparable damage to the environment and human health if not strategically disposed of.

Though waste disposal has been a matter of concern for several decades, the main problem has been taking massive proportions due to growth in population and industrialization, the two major factors that contribute to waste generation. Though some advancement is being made in waste disposal methods, they are still not adequate. The challenge is to detect newer and unhazardous methods of waste disposal and put these methods to use.

Below we will venture into six effective waste disposal methods.

1. Preventing or reducing waste generation: Extensive use of new or unnecessary products is the root cause of unchecked waste formation. The rapid population growth makes it imperative to use secondhand products or judiciously use the existing ones because if not, there is a potential risk of people succumbing to the ill effects of toxic wastes. Disposing of the wastes will also assume formidable shape. A conscious decision should be made at the personal and professional level to judiciously curb the menacing growth of wastes.

2. Recycling: Recycling serves to transform the wastes into products of their own genre through industrial processing. Paper, glass, aluminum, and plastics are commonly recycled. It is environmentally friendly to reuse the wastes instead of adding them to nature. However, processing technologies are pretty expensive.

3. Incineration: Incineration features combustion of wastes to transform them into base components, with the generated heat being trapped for deriving energy. Assorted gases and inert ash are common by-products. Pollution is caused by varied degrees dependent on nature of waste combusted and incinerator design. Use of filters can check pollution. It is rather inexpensive to burn wastes and the waste volume is reduced by about 90%. The nutrient rich ash derived out of burning organic wastes can facilitate hydroponic solutions. Hazardous and toxic wastes can be easily be rid of by using this method. The energy extracted can be used for cooking, heating, and supplying power to turbines. However, strict vigilance and due diligence should be exercised to check the accidental leakage of micro level contaminants, such as dioxins from incinerator lines.

4. Composting: It involves decomposition of organic wastes by microbes by allowing the waste to stay accumulated in a pit for a long period of time. The nutrient rich compost can be used as plant manure. However, the process is slow and consumes a significant amount of land. Biological reprocessing tremendously improves the fertility of the soil.

5. Sanitary Landfill: This involves the dumping of wastes into a landfill. The base is prepared of a protective lining, which serves as a barrier between wastes and ground water, and prevents the separation of toxic chemicals into the water zone. Waste layers are subjected to compaction and subsequently coated with an earth layer. Soil that is non-porous is preferred to mitigate the vulnerability of accidental leakage of toxic chemicals. Landfills should be created in places with low groundwater level and far from sources of flooding. However, a sufficient number of skilled manpower is required to maintain sanitary landfills.

6. Disposal in ocean/sea: Wastes generally of radioactive nature are dumped in the oceans far from active human habitats. However, environmentalists are challenging this method, as such an action is believed to spell doom for aquatic life by depriving the ocean waters of its inherent nutrients.

Effective waste disposal calls for concerted efforts from all, no matter how anxious or worried they may be about our environment.

Northern California Compactors Inc. offers installation and support services for waste recycling equipment such as trash compactors, balers, shredders & conveyor systems. Established in 1981, it offers waste management solutions across the United States.



Blanching is an operation in which a raw food material is immersed in water at 88–99° C (190–210° F) or exposed to live steam for a specified period.

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Microwave Processing of Frozen and Packaged Food Materials: Experimental

Lineesh Punathil, Tanmay Basak, in Reference Module in Food Science , 2016

Microwave Blanching of Food

Blanching is generally used for color retention and enzyme inactivation of the food materials. Enzyme inactivation is necessary to avoid undesirable enzymatic reactions occurring within the food materials. Blanching is carried out by immersing food materials in hot water, steam, boiling solutions containing acids and salts, or in a microwave applicator. Blanching is mainly carried out for vegetables, fruits, and fish.

Microwave Blanching of Vegetables

Effect of Blanching Methods

Various blanching methods such as microwave, steam, and boiling water blanching on enzyme inactivation and color changes during the blanching of artichokes (vegetable) play the significant role on the process efficiency. The complete inactivation of chlorophyllase enzyme is found to occur at 2, 6, and 8 min for microwave, steam, and boiling water blanching, respectively. The microwave and boiling water–blanched samples are greener and brighter compared to the steam-blanched samples due to the high loss of chlorophyllous pigments. It is found that 16.7% loss of ascorbic acid occurs during boiling water blanching. However, during microwave blanching, no loss of ascorbic acid is detected. Therefore, microwave blanching leads to the artichokes with better color and nutrient quality.

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Microwave blanching of herbs such as marjoram and rosemary exhibits important characteristics. The retention of color, ascorbic acid, and chlorophyll is found to be higher for the microwave-blanched samples compared to the water- and steam-blanched samples. Microwave and water blanching of vegetables (spinach, carrot, and bell peppers) can also be studied experimentally ( Figure 5 ; Ramesh et al., 2002 ). The samples can be placed in a cylindrical Pyrex bowl. In order to obtain the uniform microwave power distribution, the bowl can be placed at the periphery of the turntable. Temperature of the vegetable can be measured by the optical thermosensor. The peroxidase inactivation indicates that microwave blanching is comparable to water blanching for the low surface area to volume ratio of the vegetables (carrot and bell peppers). The loss of nutrients is found to be lower for the microwave-blanched samples compared to conventional blanching. This may be due to the occurrence of leaching losses during conventional blanching. The effect of various blanching methods such as steam, boiling water, and microwave blanching for peas exhibits various characteristics as follows. The blanched samples are evaluated for the moisture and ascorbic acid content, peroxidase activity, color, aroma, flavor, and texture. The peroxidase activity is reduced by 97% for the blanched samples compared to the unblanched samples. The ascorbic acid retention can be higher for steam blanching compared to other blanching methods. The microwave-blanched peas are found to be greener than the peas treated with the other blanching methods. However, the aroma and flavor are found to be similar for the samples treated by all the three blanching methods.

Figure 5 . Schematic of experimental setup for microwave blanching.

Reproduced from Ramesh, M.N., Wolf, W., Tevini, D., Bognar, A., 2002. Microwave blanching of vegetables. J. Food Sci. 67 (1), 390–398, with permission from John Wiley and Sons.

Inactivation of Enzyme

Polyphenoloxidase (PPO) enzyme inactivation can occur during microwave and hot water blanching of mushroom. PPO enzyme is the major enzyme responsible for browning reactions in mushrooms, and PPO inactivation can be determined by spectrophotometric method. Microwave blanching requires lesser time for the complete inactivation of enzyme compared to the hot water blanching due to the enhanced thermal effect during microwave blanching. Microwave blanching requires up to 20 s for the complete inactivation of PPO, whereas a conventional blanching method requires more than 6 min. However, the direct application of microwaves to entire mushrooms may damage the sample texture due to the internal vaporization of water.

The effect of various methods such as conventional, microwave, and combined microwave–hot water blanching for mushroom is significant ( Figure 6 ). Figure 6(a–c) shows the temperature distribution within the mushroom slices treated with conventional, microwave, and combined microwave–hot water blanching, respectively ( Devece et al., 1999 ). During conventional blanching, the temperature at the center is lower than that of the surface ( Figure 6(a) ), whereas the temperature at the surface is higher than that of the center for microwave blanching ( Figure 6(b) ). A more uniform temperature distribution can be obtained by combined microwave–hot water blanching ( Figure 6(c) ). In the case of the combined microwave–hot water blanching, the complete inactivation of PPO can be achieved in a shorter time. The loss of antioxidant content and the increase of browning can be found to be less for combined microwave–hot water blanching. The enzyme inactivation and antioxidant activity of pepper during microwave blanching can also be investigated. The spectrophotometric method can be used to determine the enzyme inactivation. A duration of 20 s may be required for complete inactivation of PPO enzyme. The antioxidant activity can be found to increase during microwave blanching. This may be due to the generation of phenolic derivatives with enhanced antioxidant activity. The inactivation of PPO and peroxidase enzymes can also occur during microwave blanching of red beet. Note that 90% of PPO is inactivated for the duration of 5 min with the microwave power of 200 W. Although PPO enzyme within red beet can be inactivated completely, the peroxidase enzyme cannot be completely inactivated at similar conditions as the peroxidase enzyme is more resistant to temperature than that of PPO enzyme. Due to the removal of water, a large weight loss and shrinkage can be observed during microwave blanching of red beet. PPO inactivation also occurs during microwave and conventional blanching of mamey fruit. Microwave blanching requires lesser time and temperature for the inactivation of PPO compared to conventional blanching. Microwave blanching also results in the negligible damage to the fruit tissue. Therefore, microwave blanching is preferred as an effective method for blanching of mamey fruit.

Figure 6 . Temperature distribution in the mushroom slices during (a) conventional hot water blanching for 1 min and 92 °C, (b) microwave blanching for 1 min at 92 °C, and (c) combined 1 min microwave blanching at 85 °C plus 20 s hot water blanching.

Reproduced from Devece, C., Rodriguez-Lopez, J.N., Fenoll, L.G., Tudela, J., Catala, J.M., de los Reyes, E., Garcia-Canovas, F., 1999. Enzyme inactivation analysis for industrial blanching applications: comparison of microwave, conventional, and combination heat treatments on mushroom polyphenoloxidase activity. J. Agric. Food Chem. 47 (11), 4506–4511, with permission from ACS publications.

Antinutritional Content

The effect of blanching methods on the content of antinutritional components in vegetables such as trypsin and chymotrypsin inhibitors is important. The trypsin and chymotrypsin contents are reduced during both microwave and conventional blanching. Therefore, blanching is an effective method for reducing trypsin and chymotrypsin inhibitor activities in vegetables.

Microwave Blanching of Fish

Effect of Blanching Methods

Microwave blanching technique can also be used to process fish. Various blanching methods such as steam, water, and the microwave blanching for desalted codfish can be employed. The color and microstructural observations of the blanched samples indicate that microwave blanching retains the color and structure compared to the other blanching methods. The effect of various blanching methods for codfish prior to freezing is found to be significant. The volatiles released during storage indicate that microwave-blanched coldfishes are less effective compared to the coldfishes blanched by other two methods.

Pathogens and Product Quality

The effect of various pretreatments such as blanching , washing, pan frying, and microwave heating is important to examine the fate of pathogens within fish. Blanching is found be the most effective method to remove the pathogens. The effect of microwave blanching on quality of vacuum and conventional polyethylene-packed sutchi catfish fillets can be analyzed. Microwave blanching increases the hardness and chewiness with the reduction in stiffness of fish samples. The storage life of the microwave-blanched and vacuum-packed sample is higher compared to unblanched vacuum-packed sample.

Effect of Packing Material

The microwave-blanched and unblanched carrot slices and sweet potatoes can be packed and stored as frozen state. The packaged microwave-blanched samples show the better quality product after a long storage compared to the packaged unblanched samples. The effect of microwave blanching on packaged sutchi catfish fillets can be studied experimentally ( Binsi et al., 2014 ). The fish samples can be packed in vacuum polyethylene or conventional polyethylene. In general, microwave blanching of fish results in a very low change in fatty acid content and mineral content. Microwave-blanched fish samples packed in vacuum packages possess longer shelf life compared to unblanched vacuum-packed samples.

Chemical Changes of Bioactive Phytochemicals during Thermal Processing

Yancui Huang, . Indika Edirisinghe, in Reference Module in Food Science , 2016


Blanching is an important intermediate thermal processing step to enhance preservation and quality of foods by inactivating enzymes that can cause loss of flavor and color. However, timing of blanching is crucial and should be appropriately adjusted for size and type of foods based on varying susceptibility to degradation with thermal processing. Underblanching stimulates enzymatic actions and increases degradation rate, whereas overblanching causes loss of texture, color, and flavor qualities. Bioactive phytochemicals can undergo chemical changes during blanching as well. The effect of blanching on chemical changes of bioactive phytochemicals depends on several factors, including the method of blanching, thermal stability of different phytochemicals, enzyme activity, and location of phytochemicals in the plant structure.

Water and steam blanching are the most common blanching methods. Water blanching involves immersion of food into boiled water. Loss of bioactive phytochemicals into water medium is a critical point for control during water blanching. Intense heat from the boiled water can lead to disruption of cellular structure increasing release of soluble bioactive phytochemicals from plant cellular compartments into the water medium ( Rungapamestry et al., 2007 ). Compared to water blanching, steam blanching or steaming results in better retention of bioactive phytochemicals in food ( Volden et al., 2009 ; Goodrich et al., 1989 ). Volden et al. (2009) reported that 30–52% loss of total glucosinolates in cauliflower occurs during water blanching compared with 18–22% loss during steaming. They also showed 10–21% reduction of total phenols in water blanching, whereas no significant reduction was found after the steaming condition ( Volden et al., 2009 ). Similarly, Nayak et al. (2011) observed that 8 min of saturated steam blanching prior to drum drying increased total antioxidant capacity (175%) of dry flakes when compared to raw purple potato. Rossi et al. (2003) reported that blueberry juice had higher recovery of phenolic compounds and strong radical-scavenging activity to DPPH and hydroxyl radicals after steam blanching for 3 min compared to the unprocessed juice.

Thermal stability of different bioactive phytochemicals is a key factor that determines the rate of degradation during blanching. Polyphenols, a subcategory of phenolic compounds, are heat sensitive. As shown by Jaiswal et al. (2012) , the degradation rate constant (first-order kinetic model using blanching temperature and time) of total polyphenolic content in Irish York cabbage increased from 0.379 to 0.484 min −1 when temperature was increased from 80 to 100 °C. Similarly, the degradation rate of phenolic compounds in almond skin followed first-order kinetics and was significantly higher after blanching at 100 °C than at 25 °C ( Hughey et al., 2012 ). It has been reported that blanching in water at 98 °C for 2 min diminishes the antioxidant capacity of purple carrots ( Uyan et al., 2004 ). Amin and Lee (2005) observed that 5–10 min of blanching in hot water at 98 °C significantly reduced (p Oboh (2005) studied the effect of water blanching on tropical green leafy vegetables and found increased total phenol content in six out of eight vegetables studied (∼33–200% gain) when blanched for 5 min in boiled water. No changes were recorded in the other two vegetables ( Oboh, 2005 ). Carotenoids in tomatoes are known for being more bioavailable after thermal processing. In a study of water blanching, lycopene and β-carotene were increased compared to fresh or unblanched tomatoes ( Urbonaviciene et al., 2012 ). The increase of bioactive phytochemicals has been ascribed to increased extractability. Increased extractability also means enhanced bioaccessibility leading to increased bioavailability ( Tibäck et al., 2009 ; Colle et al., 2010 ; Svelander et al., 2010 ). Thermal stability of bioactive phytochemicals could be different even within the same plant food source. For example, the two primary bioactive phytochemicals, lycopene and β-carotene, in the tomato, have different chemical stabilities to heat. Lycopene is more heat stable during blanching, whereas β-carotene is heat sensitive ( Nguyen et al., 2001 ) and, therefore, greater losses during blanching are observed with β-carotene compared to lycopene ( Svelander et al., 2010 ).

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Timing of blanching is another critical point of control; as treatment time increases, loss of bioactive phytochemical increases. Although blanching is usually considered a short time thermal treatment (less than 10 min), every minute counts for preserving bioactive phytochemicals. For the first 1 min of water blanching at 100 °C, flavonoids in sweet potato leaves were relatively well preserved; however, flavonoid content was immediately reduced after 2 min of blanching ( Chu et al., 2000 ). The greatest loss of bioactive compounds in cabbage and almond skins was also observed within the first 2 min of water blanching and then gradual loss was observed as blanching time increased ( Hughey et al., 2012 ). Mizrahi (1996) reported that 2 min of ohmic blanching of large whole vegetables had similar effects as 4 min of water blanching. Icier (2010) reported that ohmic blanching (25–40 V cm −1 ) of artichoke by-product was faster at inactivating the peroxidase enzyme, without producing blanching wastewater compared to hot water blanching (85 °C for 570 s holding time) thus retaining higher total phenolic content. Furthermore, they reported that ohmic blanching (40 V cm −1 ) at 85 °C (210 s holding time and 310 ± 2 s total inactivation time) had similar peroxidase inactivation as water blanching at 100 °C (300 ± 2 s) ( Icier, 2010 ).

Enzyme activity is regarded as one of the most important factors responsible for producing chemical changes in bioactive phytochemicals. Although the main goal of blanching is to inactivate enzymes responsible for textural and color qualities, inactivation of other enzymes influences retention and degradation of bioactive phytochemicals. Therefore, understanding the mechanism and critical points of bioactive phytochemicals destruction by enzymatic activity could be important in the design of an extraction procedure and perhaps in the final formulation of a food. Inactivation of certain enzymes that mediate oxidation of bioactive phytochemicals is suggested to improve their retention during blanching and even during subsequent thermal processing ( Brambilla et al., 2011 ). For example, if native polyphenol oxidase is not inactivated prior to food processing it can catalyze oxidation of polyphenols in blueberries during subsequent thermal treatment and storage ( Kader et al., 1997 ) and contribute to greater loss of polyphenols compared with the blueberries that were not pretreated/blanched ( Rossi et al., 2003 ). Skrede et al. (2000) crushed pulp from peeled blueberries (both blanched and not-blanched) and added them to pasteurized blueberry juice. Anthocyanin content was monitored over 3 h at 40 °C. They observed that pasteurized juice lost about 50% of the anthocyanin content when incubated with crushed, anthocyanin-free, peeled blueberry pulp, and the control containing blanched blueberry pulp showed no anthocyanin degradation ( Skrede et al., 2000 ). Similarly, blanching of blueberry for 3 min using steam induced 23% higher anthocyanin retention compared to 12% in the unblanched when processed into juice ( Rossi et al., 2003 ). Anthocyanin content is increased by 27% in blanched (98 °C for 2 min) purple carrots compared with the fresh sample ( Uyan et al., 2004 ). Steam blanching of purple- and red-fleshed potatoes resulted in 98–99% reduction in the peroxidase activity to retain the anthocyanins ( Reyes and Cisneros-Zevallos, 2007 ). Wolfe and Liu (2003) reported that blanching in boiling water for 10 s followed by oven drying retains or increases anthocyanin content of apple peels. Total anthocyanins (90%) in purple potatoes have been shown to be retained after steam blanching for 8 min ( Nayak et al., 2011 ). Rossi et al. (2003) showed that blanching has a beneficial effect on the recovery of individual anthocyanin in blueberry juice processing. The percent recovery increased by 71–2672% for monoglucosides of cyanidin, malvidin petunidin, peonidin, and delphidin ( Rossi et al., 2003 ). In contrast, inactivation of other enzymes during blanching can have the opposite effect. Glucosinolate requires myrosinases, an enzymatic cofactor to form isothiocyanate, which is a bioactive metabolite of glucosinolates and suggested to be the primary contributor to the health benefits of brassica vegetables. Inactivation of myrosinase during blanching may not immediately change glucosinolate concentrations; however, it can alter the glucosinolate-myrosinase system and result in reduction of total glucosinolates impacting bioavailability and possibly their health benefits ( Rungapamestry et al., 2007 ).

Location of phytochemicals within the plant/fruit structure varies and thus blanching may have different effects on bioactive phytochemicals of different plant foods. For example, blueberries and raspberries are rich in anthocyanins although their content and distribution within the plant differ, impacting extractability and susceptibility to degradation. During blanching, anthocyanins in blueberries had increased extractability when compared to unblanched blueberries, whereas anthocyanins in red raspberry were not affected by blanching ( Sablani et al., 2010 ). In blueberries, anthocyanins are concentrated in the skin, and blanching can induce tissue/cellular rupture and cause significant anthocyanin release from skin and vacuole increasing the extractability of anthocyanin compounds as well as enhance some degradation ( Brambilla et al., 2011 ). In contrast, red raspberries have anthocyanins distributed throughout the fruit flesh, which may be a reason for the undetected changes of raspberry anthocyanins during blanching ( Sablani et al., 2010 ).

Canning with pulses and pasta

4.9.2 Preparation of spaghetti

Blanching . The use of saltwater (4–7% salt) for blanching is preferable, in that the product remains firm and does not become as sticky as in water. However, water alone is used by some canners. During blanching, either in saltwater or water alone, it is necessary to stir the spaghetti some to secure uniform blanches and to keep the spaghetti from sticking together. Blanching spaghetti is usually done in batches and is commonly carried out by placing the dry spaghetti in a wire basket that is lowered into rapidly boiling water in a large kettle or by placing dry spaghetti in large steam-jacketed stainless steel kettles and removing it after blanching by means of large perforated ladles or forks.

Blanching for 10–20 min in boiling water is required for most types of spaghetti. The time depends on the gain in weight desired in the blanched spaghetti and on the texture desired in the finished product after it has been processed. During the blanching, the weight increases about two and one-half times.

Cooling and washing. After being blanched, the hot spaghetti should be cooled at once, either by plunging it into cold water or passing it under sprays of cold water. This washes any free starch from the surface and firms it. The blanched spaghetti should be kept in cold water until filled.

POTATOES AND RELATED CROPS | Processing Potato Tubers


Blanching means a short-term heat treatment (70–100 °C) of raw potatoes or potato pieces. Several reactions occur. Enzymes are inactivated (e.g., polyphenoloxidase) to prevent discoloration. Often the peroxidase system is regarded as a key enzyme mirroring the efficiency of enzyme inhibition. Reducing sugars are leached off, to minimize the Maillard reaction, as well as starch pastes, to reduce fat uptake during frying. Blanching for about 20 min at 70–75 °C results in a firm structure. Native pectin methyl esterase is activated to reduce cross-linking of pectin, and free carboxyl groups may react with calcium or magnesium liberated from starch granules after gelatinization to form a thermostable pectin network. The addition of calcium to the blanching water intensifies that reaction.

Blanching takes place predominantly in a continuous screw motion through a water bath or through a steam chamber. Depending on the raw material and the shape of single pieces, blanching parameters vary widely.

Blanching as a Treatment Process

Nissreen Abu-Ghannam, Amit Kumar Jaiswal, in Processing and Impact on Active Components in Food , 2015


Blanching is a short heat treatment that is typically applied to vegetables prior to further processing with the aim of enhancing both safety and quality attributes. It imparts benefits such as the destruction of surface microflora on vegetables and the enhancement of the color, texture and also the keeping quality of vegetable products ( Jaiswal et al., 2012c ). In addition, blanching is essential for vegetable products destined for further storage such as freezing or drying in order to inactivate certain enzymes including lipoxygenase, polyphenololoxidase, polygalacturonase, and chlorophyllase which are associated with losses in quality and nutritional properties. Apart from blanching, other processing methodologies of vegetables, including drying and freezing, are insufficient to inactivate these enzymes thus leading to deterioration in texture, color, and flavor during storage.

The quality of blanched products depends significantly on the time–temperature combinations of blanching and also on the vegetable type. Under-blanching speeds up the activity of enzymes and is worse than no blanching ( Jaiswal et al., 2012c ). Over-blanching causes losses in texture, color, phytochemicals and minerals. Typically, industrial blanching processes utilize temperatures ranging from 70 to 95°C and times are usually within 10 min ( Morales-Blancas et al., 2006 ); whereas for domestic purposes vegetables are generally blanched, or given an extended blanching period which ultimately leads to cooking, for 10–15 min in water at temperatures ranging from 95–100°C.

Generally, blanching is carried out by the application of a wet medium such as steam or hot water in order to provide uniform heating and a high-heat transfer rate. Both in domestic and industrial processing, several blanching methods may be employed such as conventional water blanching, microwave, or steam blanching; the regime being dictated by the nature of the raw material and the desired properties of the final product. Traditionally, blanching is carried out either at a low temperature (55–75°C) for long-time, typically referred to as LTLT or high-temperature short-time (80–100°C) for less than 10 min, referred to as HTST depending upon the type of vegetable ( Abu-Ghannam and Crowley, 2006 ). Conventional water blanching usually imparts more uniform processing. However, prolonged water blanching results in considerable losses in phytochemicals and antioxidant properties ( Jaiswal et al., 2012c ).

Microwave heating is three- to five-times faster than conventional heating and relies on the application of dielectric heating. This is accomplished by using microwave radiation to heat water and other polarized molecules within the food, leading to heat generation in the entire volume at the same rate due to internal thermal dissipation of water molecule vibrations in the food ( Kamel and Stauffer, 1993 ). It has advantages over conventional heating methods such as precision timing, speed, and energy saving.

Steam blanching is generally carried out in a steam blancher where the vegetable product is exposed directly to a food-grade steam typically at a temperature close to 100°C. Steam blanching results in minimum losses in phytochemicals and antioxidant capacity ( Faller and Fialho, 2009; Podsędek et al., 2008; Turkmen et al., 2005; Wachtel-Galor et al., 2008 ); furthermore, it requires less time than conventional blanching because the heat transfer coefficient of condensing steam is greater than that of hot water and it is proven to be comparatively economical as it saves energy ( De Corcuera et al., 2004 ).

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Microwave Blanching

Lidia Dorantes-Alvarez, . Lidia Parada-Dorantes, in Reference Module in Food Science , 2017

Microwave Blanching Effects in Ultrastructure of Foods

Blanching causes physical and metabolic changes within food cells. Heat damages cytoplasmic and other membranes, which become permeable and result in a loss of cell turgor ( Fellows, 2009 ). Water and solutes pass into and out of cells (leaching), resulting in nutrient losses. Heat also disrupts subcellular organelles, and their constituents become free to interact within the cell.

Studies have reported that microwave blanching could be superior to conventional blanching methods keeping the cell structures intact and maintaining porosity of dried materials ( Kowalska et al., 2008 ). In drying of red bell peppers, hot water blanching, microwave blanching, and infrared blanching showed differences in ultrastructure: it was observed that the control sample had smooth cell walls with abundant plastoglobuli and integrated plastids. The sample treated with hot water blanching showed disrupted plastids with the grana segregated from cell walls. In addition, the thylakoids were completely collapsed and the plastids were dispersed into the intercellular space. This phenomenon explained the maximum loss of red pigments and ascorbic acid. In samples treated by microwave and infrared blanching, the segregation of plastids from cell walls was also observed, while the tylakoids were still stacked ( Wang et al., 2017 ).

The effect of hot water (90 °C) and microwaves (power of 350 and 900 W) on cell wall characteristics of red beet were analyzed. Traditional blanching of red beet root tissue produced a great impact mainly at the cell corners with clear separation of the middle lamella. 350 W-treated tissue also showed separation of the middle lamellae at the cell corners but contacts between all neighboring cells persisted and were clearly observed after the microwave treatment. Powers higher than 900 W produced greater microstructural tissue damage due to alteration of the cell wall network ( Latorre et al., 2013 ). After MAB, freeze-dried Thunbergia laurifolia leaves had a more porous and uniform cell structure, with less tissue shrinkage and collapse compared to other dried samples ( Phahom et al., 2017 ).

Acrylamide in Potato Products

2.7 Blanching Process

Blanching is an important unit operation in the industrial process of french fry production and its complexity may differ between production lines (e.g., the use of one, two, or three blanchers). During this step enzymes are inactivated and a layer of gelatinized starch is formed, which limits oil absorption and improves texture ( Moreira et al., 1999 ). In addition, blanching also contributes to a uniform color of the product after final frying. Moreover, during this step, acrylamide precursors are leached out, resulting in the reduction of acrylamide content in the final product ( Pedreschi et al., 2004; Pedreschi et al., 2007c; Mestdagh et al., 2008b; Pedreschi et al., 2009; Medeiros et al., 2010; Viklund et al., 2010 ). Blanching conditions (time and temperature) therefore can be manipulated until an optimized reducing sugar extraction is reached. To keep the final product specifications constant, potato processors typically increase the intensity of blanching conditions toward the end of the potato season owing to senescence sweetening. However, extreme blanching conditions result in textural and nutrient loss issues and therefore blanching can be adapted only within certain limitations. Mestdagh et al. (2008b) reported an acrylamide reduction of 65% and 96% for french fries and potato crisps, respectively, after blanching (70 °C, 10–15 min). In addition to time and temperature, the concentration of soluble components extracted from the potato cuts during this continuous process will also influence the efficiency of sugar extractability and therefore affect acrylamide formation in potato products. A decrease in sugar extraction of 10% was ascribed to the concentration of soluble components in the blanching water compared to extraction rates in fresh water ( Mestdagh et al., 2008b ). On the other hand, the continuous replacement of the blanching water with fresh water is not feasible, from both environmental and economical points of view. Moreover, since in general dextrose is added in the subsequent step (as discussed below), this aspect becomes less relevant on the acrylamide content of the final product.

CANNING | Food Handling


Blanching is a heat treatment in a near-boiling water or steam followed by rapid cooling given to vegetables and some fruit. Blanching removes gases from within the tissue and softens the product. Blanching makes the product easier to fill into the can and to obtain the correct fill weight. The removal of the gas also reduces the oxidation of the product, maintains the vacuum in the can, and prevents excessive can corrosion.

Blanching gives the product another washing treatment and inactivates enzymes which may cause deterioration of the food. Enzyme inactivation is not as important for canned foods as it is for frozen foods, as canned foods receive a far greater heat treatment during thermal processing of the can. It can be important if there is a long delay between filling the can and retorting. Typical blanch times in near-boiling water are 60–90 s for small objects, such as green peas and diced carrot, and up to 3 min for larger pieces.

Canning operations

10.7 Blanching

Blanching is an operation in which a raw food material is immersed in water at 88–99° C (190–210° F) or exposed to live steam for a specified period.

The objectives sought in blanching are not always the same but vary according to maturity and product for one or more of the following reasons:

Inhibition of enzymatic action. Natural product enzymes are inactivated by blanching, and thus undesirable changes in colour and flavour are avoided, as well as reduction in the content of certain vitamins.

Expelling of respiratory gases. Raw fruits and vegetables contain intracellular gases, of composition similar to that of air, but somewhat higher than air in oxygen and carbon dioxide content. The release of gases prevents strain on can seams during heat processing and assists in the development of high vacuum in the finished product. Another desirable effect is a reduction in internal can corrosion by reducing oxygen content of can-headspace gases. Headspace oxygen acts as a depolariser in electrochemical corrosion reactions, thus increasing rate of corrosion.

Softening of food. Product becomes easier to fill in the container, and higher drained weights are obtained.

Facilitating preliminary operations. Peeling, dicing, cutting, and other preparatory steps are accomplished more easily and efficiently.

Setting the natural colour of certain products and preventing oxidative browning in others.

Removing undesirable raw flavours from food.

Blanching also aids in cleaning the product.

Blanching is usually accomplished in equipment especially designed for individual products. The equipment must be designed so that it is possible to subject raw materials to a particular temperature range for a proper period. The shortest blanching time that accomplishes the desired objectives usually gives the best product. Many vegetables and some fruits are blanched.

Continuous hot water blanchers are usually of the following two types:

Immersion or conveyor type, employing either screw or chain conveyors by which the product is moved through a tank of hot water.

Hydraulic type, called a pipe or tubular blancher, in which the product is conveyed in hot water through numerous lengths of pipe by a circulating pump and aided by steam jets.

Continuous steam type blanchers are mechanically more complex than hot-water types. They continuously move the product through a tank containing live steam using a chain or belt conveyor.

The main disadvantage of hot-water blanching is the large volume of water needed and its direct contact with the product, which may result in some leaching of water-soluble food constituents such as vitamins, minerals, sugars, and starch. Results of research on several specific nutrients indicate a wide variability in nutrient losses caused by either hot water or steam blanching.

The leaching of water-soluble substances also results in increased biological oxygen demand (BOD) of liquid effluents discharged from processing plants, increasing costs of disposal. There is obvious need for modifying processing operations to reduce and, whenever possible, eliminate the amount of pollution generated. On average, over 40% of total plant effluent BOD in vegetable processing is generated by blanching.

Hot-gas blanching has been demonstrated to reduce the volume of wastewater effluent from a blancher to less than 1% of that produced with steam or hot-water blanching. In pilot plant studies, hot-gas blanching has been found applicable to several commercially important vegetables, with the exclusion of cob corn or beets. In hot-gas blanching, vegetables are heated by means of combustion or flue gases from a gas burner. Hot flue gases are recirculated upwards through the vegetables which are conveyed through the blancher between two wire-mesh belt conveyors. Steam is added to the recirculating flue gases to increase relative humidity, minimise partial drying, and facilitate heat transfer, which would otherwise result in weight losses. The data obtained indicate that hot gas-blanched vegetables have quality well within the range of commercial acceptability. Overall results from studies on nutrient retention show no significant difference due to type of blanching received by the vegetable samples investigated. It is reported that hot gas-blanched spinach and peas show higher retention of ascorbic acid (vitamin C) than either hot-water or steam blanching. However, product weight loss with hot-gas blanching has been found to be higher for many vegetables. Hot-gas blanching is still at the developmental stage for commercial application. (When a blanched food product is washed prior to filling, potable water should be used.)

PASTEURIZATION | Other Pasteurization Processes


Although blanching is not traditionally seen as a pasteurization process, some authors deem it to be a ‘kind’ or ‘type’ of pasteurization. While pasteurization, however, has as its main function the destruction of pathogenic microorganisms, it also destroys certain natural food enzymes in the process. Blanching, however, is applied primarily to inactivate natural enzymes in fruits and vegetables to be processed. Its secondary effect is that it reduces the microbial load. Both pasteurization and blanching are similar in that they employ temperatures below 100 °C.

A process involving acid blanching and the addition of ethylenediaminetetraacetic acid to a canning brine has been a recent topic of research. The results have shown potential with regard to the control of spoilage and botulinal toxigenesis in canned products. This draws a further parallel between blanching (a preparatory method) and pasteurization (a processing method). (See CANNING | Principles .)

With this in mind, the reader is referred to the article on canning for further information.

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