The Freezing Of Time ~REPACK~

[Irmela Caccavale]

<div>Freezer type. The type of freezer will greatlyinfluence the freezing time. For example, due to improved surfaceheat transfer, a product will normally freeze faster in animmersion freezer than in an air blast freezer operating at thesame temperature.</div><div></div><div></div><div>Air speed in blast freezers. The general relationshipbetween air speed and freezing time is shown in Figure 5 and thisshows that freezing time is reduced as the air speed is increased.This, however, is a rather complicated relationship and itdepends on a number of factors. If the resistance to heattransfer of the stagnant boundary layer of air is important,changes in air speed will make a significant difference to thefreezing time. If, however, the package is large and theresistance of the fish itself is the important factor thenchanges in air speed will be less significant. Air temperature,air density, air humidity and air turbulence are other factorsthat have to be taken into account when the effect of aircondition on freezing time is considered. Some of these factorshowever, may only have a minor effect.</div><div></div><div></div><div></div><div></div><div></div><div>The freezing of time</div><div></div><div>Download: https://t.co/Xrxkyqp9SE </div><div></div><div></div><div>Product thickness. The thicker the product, the longeris the freezing time. For products less than 50 mm thick,doubling the thickness may more than double the freezing timewhereas doubling a thickness of 100 mm or more may increase thefreezing time fourfold. The rate of change of freezing time withthickness therefore, depends on the relative importance of theresistance of the fish to heat transfer.</div><div></div><div></div><div>Product contact area and density. In a plate freezer,poor contact between product and plate results in increasedfreezing time. Poor contact may be due to ice on the plates,packs of unequal thickness, partially filled packs or voids atthe surface of the block. Surface voids are often accompanied byinternal voids and this also results in poor heat transfer. Apartfrom increasing freezing time, internal voids also reduce thedensity of the block. The relationship between time, blockdensity and contact area for 100 mm blocks of white fish is shownin Table 6.</div><div></div><div></div><div>Product packaging. The method of wrapping and the typeand thickness of the wrapping material can greatly influence thefreezing time of a product. Air trapped between wrapper andproduct has often a greater influence on the freezing time thanthe resistance of the wrapping material itself. The followingexample illustrates the point. Smoked fish in a cardboard boxwith the lid on take 15h to freeze in an air blast freezer.Smoked fish in an aluminium box of the same shape and size andwith the lid on take 12h, but if the lid is taken off thecardboard box, the freezing time is only 8h because there is notrapped air acting as an insulation.</div><div></div><div></div><div>Species of fish. The higher the oil content of the fishthe lower is the water content. Most of the heat extracted duringfreezing is to change the water to ice; therefore, if there isless water, then less heat will require to be extracted to freezethe fish. Since the fat content of oily fish is subject toseasonal variations, it is safer to assume the same heat contentfigure used for lean fish in any calculation. This also ensuresthat the freezer capacity is adequate whatever the species offish being frozen.</div><div></div><div></div><div>Freezing times can be calculated, but there is usuallyinsufficient information available to make this calculationaccurate. Calculated freezing times can be fairly accurate foruniformly shaped products such as blocks of fillets but, forother products with irregular shapes, calculation can only give arough guide. The presence of wrappers and many other factors canmake calculation of the freezing time difficult and unreliable.</div><div></div><div></div><div>Formulae that have been used for quick calculations in thepast had to be simplified to make them practical. They alsoassume that the fish has been chilled before freezing and thatall of the heat is extracted at the initial freezing temperature.Calculated freezing times should therefore only be used to givean approximation of the true figure and should not be used fordesigning freezing equipment. Modern computer techniques have nowmade it possible to calculate freezing times more precisely.</div><div></div><div></div><div>Plank's formula for calculating the freezing time of fish hasbeen widely used in a variety of forms. It has proved to beparticularly valuable in extending the results from experimentalstudies to cover a wide range of variables. Thus, if anaccurately measured freezing time is known, others can becalculated if most of the freezing conditions are similar.</div><div></div><div></div><div></div><div></div><div></div><div></div><div>From the above formula, it can be seen that freezing time isinversely proportional to the temperature difference and,depending on other conditions, it may also be nearly proportionalto the square of the product thickness. This knowledge can beused to calculate other freezing times as shown in the examplesshown in Table 8.</div><div></div><div></div><div>Freezing time is directly proportional to the square of thethickness since in this case the surface heat transfercoefficient is high and the factor relating to the thickness ofthe block, PD/f, will be small. The new freezing time willtherefore be calculated as follows:</div><div></div><div></div><div>One of the many pains of working with the October 2008 CTP of VS2010 (aka Rosario) is that on top of everything else, it actually timebombed on January 1st 2009. This means that you have to run the virtual machine disconnected from the clock. Unsurprisingly all of the virtualization packages on the market try their hardest to do you doing crazy things like that. For a start, both VMWare and Virtual PC will set the CMOS clock date/time to be the time that you created / converted the machine. This means you have to be lightening fast on your F2 button to get into the BIOS setup screen to set the clock back.</div><div></div><div></div><div>You also need to tell the virtual machine to disable clock synchronization. Brian Keller has a blog post on how to do this with Microsoft Virtual PC. However, I needed to figure it out on VMWare Fusion. Luckily the following PDF from VMWare came to my rescue ( _timekeeping.pdf). The document is a little painful to read through, but basically all you need to do is open up the .vmx file in TextEdit and add the following entries:</div><div></div><div></div><div>Trichina and other parasites can be destroyed by sub-zero freezing temperatures. However, very strict government-supervised conditions must be met. Home freezing cannot be relied upon to destroy trichina. Thorough cooking, however, will destroy all parasites.</div><div></div><div></div><div>Freshness and quality at the time of freezing affect the condition of frozen foods. If frozen at peak quality, thawed foods emerge tasting better than foods frozen near the end of their useful life. So freeze items you won't use quickly sooner rather than later. Store all foods at 0 F or lower to retain vitamin content, color, flavor and texture.</div><div></div><div></div><div>Enzyme activity does not harm frozen meats or fish and is neutralized by the acids in frozen fruits. But most vegetables that freeze well are low acid and require brief, partial cooking to prevent deterioration. This is called "blanching." For successful freezing, blanch or partially cook vegetables in boiling water or in a microwave oven. Then rapidly chill the vegetables prior to freezing and storage. Consult a cookbook for timing.</div><div></div><div></div><div>Proper packaging helps maintain quality and prevent freezer burn. It is safe to freeze meat or poultry directly in its original packaging, however this type of wrap is permeable to air and quality may diminish over time. For prolonged storage, overwrap these packages as you would any food for long-term storage. It is not necessary to rinse meat and poultry. Freeze unopened vacuum packages as is. If you notice that a package has accidentally been torn or has opened while food is in the freezer, the food is still safe to use; merely overwrap or rewrap it.</div><div></div><div></div><div></div><div></div><div>Freeze food as fast as possible to maintain its quality. Rapid freezing prevents undesirable large ice crystals from forming throughout the product because the molecules don't have time to form into the characteristic six-sided snowflake. Slow freezing creates large, disruptive ice crystals. During thawing, they damage the cells and dissolve emulsions. This causes meat to "drip" and lose juiciness. Emulsions such as mayonnaise or cream will separate and appear curdled.</div><div></div><div></div><div>If a refrigerator freezing compartment can't maintain zero degrees or if the door is opened frequently, use it for short-term food storage. Eat those foods as soon as possible for best quality. Use a free-standing freezer set at 0 F or below for long-term storage of frozen foods. Keep an appliance thermometer in your freezing compartment or freezer to check the temperature. This is important if you experience power-out or mechanical problems. The temperature in the refrigerator should be set at 40 F or below. Check the refrigerator temperature with an appliance thermometer.</div><div></div><div></div><div></div><div></div><div>Because freezing keeps food safe almost indefinitely, recommended storage times are for quality only. Refer to the freezer storage chart at the end of this document, which lists optimum freezing times for best quality.</div><div></div><div></div><div>Raw or cooked meat, poultry or casseroles can be cooked or reheated from the frozen state. However, it will take approximately one and a half times as long to cook. Remember to discard any wrapping or absorbent paper from meat or poultry.</div><div></div><div></div><div>A freezer full of food will usually keep about 2 days if the door is kept shut; a half-full freezer will last about a day. The freezing compartment in a refrigerator may not keep foods frozen as long. If the freezer is not full, quickly group packages together so they will retain the cold more effectively. Separate meat and poultry items from other foods so if they begin to thaw, their juices won't drip onto other foods.</div><div></div><div></div><div>To determine the safety of foods when the power goes on, check their condition and temperature. If food is partly frozen, still has ice crystals, or is as cold as if it were in a refrigerator (40 F), it is safe to refreeze or use. It's not necessary to cook raw foods before refreezing. Discard foods that have been warmer than 40 F for more than 2 hours. Discard any foods that have been contaminated by raw meat juices. Dispose of soft or melted ice cream for quality's sake.</div><div></div><div> dd2b598166</div>