FOOD AS THOUGHT
Mar 7 - 13, 2011
Shelf life is the length of time that food, beverage, medicine, and many other perishable items are given before they are considered unsuitable for sale, use, or consumption. In some regions, a best before, use by or freshness date is required on packaged perishable foods. Shelf life is the recommendation of time that products can be stored, during which the defined quality of a specified proportion of the goods remains acceptable under expected (or specified) conditions of distribution, storage, and display.
Most shelf life labels or listed expiry dates are used as guidelines based on normal handling of products. Use prior to the expiration date does not necessarily guarantee the safety of a food or drug, and a product is not always dangerous nor ineffective after the expiration date.
The United States Department of Defense (DoD) Shelf-Life Program defines shelf-life as: "The total period of time beginning with the date of manufacture, date of cure (for elastomeric and rubber products only), date of assembly, or date of pack (subsistence only), and terminated by the date by which an item must be used (expiration date) or subjected to inspection, test, restoration, or disposal action; or after inspection/laboratory test/restorative action that an item may remain in the combined wholesale (including manufacture's) and retail storage systems and still be suitable for issue or use by the end user."
Shelf life is not to be confused with service-life defined as to quantify the average or standard life expectancy of an item or equipment while in use.
Shelf life is different from expiration date. The former relates to food quality, the latter to food safety. A product that has passed its shelf life might still be safe, but quality is no longer guaranteed. In most food stores, shelf life is maximized by using stock rotation, which involves moving products with the earliest sell by date to the front of the shelf, meaning that most shoppers will pick them up first and so getting them out of the store. This is important, as some stores can be fined for selling out of date products, and most if not all will have to mark such products down as wasted, leading to a loss of profit.
Shelf life is most influenced by several factors: exposure to light and heat, transmission of gases (including humidity), mechanical stresses, and contamination by things such as microorganisms. Product quality is often mathematically modelled around a parameter (concentration of a chemical compound, a microbiological index, or moisture content). For some foods, the shelf life is an important factor to health. Bacterial contaminants are ubiquitous, and foods left unused too long will often acquire substantial amounts of bacterial colonies and become dangerous to eat, leading to food poisoning.
However, the shelf life itself is not an accurate indicator to the food safety. For example, pasteurized milk can remain fresh for five days after its sell-by date if it is refrigerated properly. In contrast, if milk already has harmful bacteria, the use-by dates become irrelevant. Similarly, the expiration date of pharmaceuticals specifies the date the manufacturer guarantees the full potency and safety of a drug. Most medications are potent and safe after the expiration date. A rare exception is a case of renal tubular acidosis purportedly caused by expired tetracycline.
Some degradation factors can be controlled by use of appropriate packaging. Packaging with barrier materials (e.g. low moisture vapor transmission rate, etc.) extends the shelf life of some foods and pharmaceuticals. Preservatives and antioxidants may be incorporated into some food and drug products to extend their shelf life. Some companies use induction sealing and vacuum pouches to assist in the extension of the shelf life of their products.
Nearly all chemical reactions will occur (at various rates depending on the individual nature of the reaction) at common temperatures. Examples are the breakdown of many chemical explosives into more unstable compounds. These breakdown processes characteristically happen more quickly at higher temperatures.
The usually quoted rule of thumb is that chemical reactions double their rate for each temperature increase of 10 degrees Celsius (∞C) because activation energy barriers become more easily surmounted at higher temperatures. It is often applied in shelf life estimation, sometimes wrongly. There is a widespread impression, for instance in industry, that "triple time" can be simulated in practice by increasing the temperature by 15 ∞C, e.g., storing a product for one month at 35 ∞C simulates three months at 20 ∞C. There is enough variation that this practical rule cannot be routinely relied upon. In the particular case of bacteria and fungi, the reactions needed to feed and reproduce increase at higher temperatures, up to the point that the proteins and other compounds in their cells themselves begin to break down, or denature, so quickly that they cannot be replaced. This is the reason high temperatures kill bacteria and other micro organisms; 'tissue' breakdown reactions reach such rates that they cannot be compensated for and the cell dies. Just as temperature increases speed up reactions, temperature decreases reduce them. Therefore, to make explosives stable for longer periods, or to keep rubber bands springy, or to force bacteria to slow down their growth, they can be cooled. This is the reason shelf life is generally extended by temperature control: (refrigeration, insulated shipping containers, controlled cold chain, etc.) and the reason some medicines and foods must be refrigerated.
Best before: Best before or best by dates appear on a wide range of frozen, dried, tinned, and other foods. These dates are only advisory and refer to the quality of the product, in contrast with use by dates, which indicate that the product is no longer safe to consume after the specified date. In spite of this, about a third of food bought is thrown away while still edible. In fact, food kept past the best before date will not necessarily be harmful, but may begin to lose its optimum flavor and texture. Sometimes, the packaging process involves using pre-printed labels, making it impractical to write the best before date in a clearly visible location. In this case, a term like best before see bottom or best before see lid might be printed on the label and the date marked in a different location as indicated.
Foods that have a best before date are usually safe to eat after the date has passed, although they are likely to have deteriorated either in flavour, texture, appearance or nutrition.
Generally, foods that have a use by date written on the packaging must not be eaten after the specified date. This is because such foods usually go bad quickly and may be injurious to health if spoiled. It is also important to follow storage instructions carefully for these foods (for example, product must be refrigerated).
Bathroom products/toiletries usually state a time in months by which, once the product is opened, they should be used. This is often indicated by a graphic of an open tub, with the number of months written inside (e.g., "12M" means use the product within 12 months of opening).
Open Dating is the use of a date or code stamped on the package of a food product to help determine how long to display the product for sale. It is also beneficial to the customer and ensures that the product is at its best quality when bought. An Open Date does not supersede a Use by date, which should still be followed.
These dates are intended to help keep track of the stock in stores. Food that has passed its sell by or display until date, but is still within its use by/best before will still be edible, assuming it has been stored correctly. It is common practice in large stores to throw away such food, as it makes the stock control process easier. It also reduces the risk of customers buying food without looking at the date, only to find out the next day that they cannot use it. Tampering with the posted date is illegal in many countries.
Most stores will rotate stock by moving the products with the earliest dates to the front of shelving units, which allows them to be sold first and saving them from having to be either marked down or thrown away, both of which contribute to a loss of profit.
HOW TO ENHANCE BEST BEFORE/USE BY DATES?
There are many ways to enhance best before and use-by dates. These include a better education of retailers and consumers on how to use, transport and store fresh food products, and improvements in domestic refrigerator performance.
TYPES OF FOODS
Not only does the shelf life of your food depend on the way in which it has been stored at home, the way it has been handled, treated and stored before arriving at your local supermarket also plays a crucial role in how long your food will stay fresh.
BUYING YOUR FOOD
Where you buy your food is very important. You should always buy your food, especially highly perishable products and products that are susceptible to contamination, from a reliable source.
It is usually better to buy fresh produce from a big supermarket where there is a high turnover and the shelves are refilled every day. However, some supermarkets have large warehouses and storerooms where fresh food could be sitting in cardboard boxes for days before they are taken out onto the shop floor and stored correctly. At the same time, supermarkets use a lot more chemicals and plastic packaging to store and preserve fresh produce, which may extend the shelf life of the food but perhaps to the detriment of the taste, nutritional value and your health. This could leave them more open to contamination, loss of freshness and nutritional value and damage. Always inspect the produce before you buy it and don't buy anything that looks too dry, discolored, limp, soft or generally not fresh. The same applies to packaging; don't buy any boxes or tins that are dented or any packets that have been ripped open or torn. When purchasing meat or fish from your local butcher or fishmonger, you are able to keep more of a control on how far your food has travelled, how it has been reared, slaughtered, prepared and stored and how long it has been sitting on the shelf, which are all factors that affect not only the quality of the food that we are consuming but also how long it will stay fresh.
Buying fresh fruit and vegetables from your local market is often the most economical choice. There is usually a much wider variety of the same types of fruit and vegetable, although care must still be taken when buying. Markets do not have the same standards as supermarkets when it comes to acquiring fresh produce from the farmer. Supermarkets are much more strict and will only accept fruits if they are the correct size, shape and quality, whereas markets will more or less accept any produce whatever the shape or size. This has however led many people to complain that supermarket fruit and vegetables are losing their flavor and aroma, as farmers must ensure that appearance is the most important factor if they want to sell their produce. Never leave these foods in the boot of your car whilst you continue to shop; they must be taken home as soon as possible after purchasing and stored in the refrigerator or freezer immediately upon returning home
STORING YOUR FOOD
Different types of foods require different storage conditions and not all foods can be stored in the same way or for the same amount of time.
Some foods will need to be stored in the refrigerator, whilst others can be kept at room temperature in a cupboard or pantry. Freezing is a really useful way of extending the shelf life of a certain product and ensuring that it does not lose valuable nutrients. Foods that are going to be stored in the refrigerator or freezer should be done so as soon as possible.
To extend the shelf life of your fresh produce, it is not only vital that it is stored in the correct place in your kitchen, but how it is packaged and where it is positioned in comparison to other foods are also imperative.
COOKED AND UNCOOKED FOOD
Fresh meat such as beef and lamb can be stored in the refrigerator for up to 5 days before being cooked, but should be eaten within 2 - 3 days when cooked.
On the other hand poultry, fish and shellfish must be cooked within 1 or 2 days after purchase, but will stay fresher for longer once cooked and can be stored in the refrigerator for 3 - 4 days maximum.
Processed meats such as pre-packaged sausages or salami, will stay fresher for longer, as they have been chemically manipulated and also contain additives and preservatives such as salt, sugar, vinegar or certain chemical compounds.
Cooked rice can be kept in the refrigerator for up to 5 - 7 days, however, with all leftover food, it is best consumed as soon as possible after cooking.
OPENED AND UNOPENED FOOD
Tinned foods should not be stored in the refrigerator. However, once a tin of food has been opened, it should be treated as if it were fresh. This means that when you open a tin of tuna fish or baked beans, the amount that you do not use should be stored in the refrigerator and will then only stay fresh for a matter of a few days.
Never store an open tin of food in the refrigerator. Always transfer the leftover tinned food into an airtight plastic container with a lid, as the tin and air will react with the contents and spoil the food.
With regards to other types of foods such as pasta, cereal, milk and various dairy products, they will always last longer if left unopened. Once a product is exposed to oxygen, heat, moisture and bacteria, the quality will start to deteriorate and its flavor, taste and appearance will begin to change.
This is the same for products such as fruit juice, mayonnaise, and ptÈ in a jar. These foods will stay fresh for several weeks if left unopened, however once opened they may need to be consumed within a much smaller period of time, usually a matter of days or weeks.
Once a food item is opened it is best to consume the product as quickly as possible.
All foods will contain one form of dating on it. For foods that tend to stay fresher for longer, this will be a "best before" date, whilst highly perishable items usually contain a "use-by" date.
Dried herbs and spices add a lot of flavor to our dishes and they are easily available and convenient to use. When we blend a combination of spices and herbs we end up with a whole variety of wonderful and unusual tastes. Preserving the quality, freshness and flavor of your seasonings will give you great tasting dishes and really will spice up your palette.
Spices do not spoil but they do lose their strength. Stored in airtight containers in cool dry places, spices retain their potency longer than you might have been led to believe. Whole peppercorns, nutmegs and cinnamon sticks tend to hold on to their flavor for a long time. And potent whole spices, such as cloves, cumin, and cardamom will also last for a long time.
The greatest importance in getting the best taste and value out of your herbs and spices is to store them well. Store them in tightly sealed containers in a cool dark place. Keeping containers tightly closed will protect them from moisture and oxidation, and they retain more of their essential oil content when stored in glass jars or metal tins. Keeping them away from direct light will keep color from fading.
Never store them above your stove or near other heat sources as heat will degrade the quality. Also, keep them away from the heat of the stove and the humidity of the dishwasher. If you have ever heard it is good to freeze spices and herbs forget it. Condensation will be a problem each time the bottle comes out of the freezer and is likely to introduce moisture to the spices. And, don't shake herbs or spices out of the bottle directly into something you're cooking as that will introduce moisture to your spices.
Red spices like chili powder, cayenne pepper and paprika can be refrigerated to prevent loss of color and flavor. Spices such as turmeric, curry powders, ground cloves, and paprika should be stored in glass or metal containers as their flavors will lessen if left in original packaging. The best temperature for herbs and spices is below 70∫ F.
Whole spices keep the longest because they have not been cracked or ground which would expose their flavors to air. Ground spices have a shorter shelf life. To determine whether or not ground spices are still viable gently shake the container with the cap on. Remove the cap after a moment and smell the container to see if the rich smell of the spice is still present.
The government recommendations for freshness dating is four years for whole spices and two years for ground and you may hear people say that spices should be replaced every six months. But, most spices are only harvested once a year, so it certainly doesn't make sense to replace these every six months.
If spices and herbs are kept as we have discussed the shelf life will be as follows:
Whole spices and herbs leaves and flowers will keep 1 - 2 years.
Seeds will keep 2 - 3 years and roots will keep 3 years.
Ground spices and herb leaves and seeds keep 1 year.
Ground roots will keep for 2 years.
A good practice to follow is to purchase high quality dried herbs and spices in small quantities so that you can easily use them up in reasonable time.