Do you know that vomit-inducing smell that comes from the expired food items? Well, you do, and you only have to smell it once to make sure it never happens again.

Today, many food items come with labels – “Sell By”, “Best By”, or “Use By” date – stamped on the packaging. Those are expiration dates. But what do they actually mean?

Consumers believe expiration dates on food items indicate if the food is safe for consumption. However, the labels are mainly for quality and flavour purposes, and have nothing to do with safety. Most foods are edible past what’s written on the label.

Also, it turns out that the FDA authorises manufacturers to sell almost any food past the expiry dates. The decision of whether to put dates on the foods lies entirely up to the manufacturers.

Study also shows that the labels have caused widespread misinterpretation among consumers, and contributed to millions of pounds of wasted food each year. Time reported that more than 90 percent of Americans discard their food prematurely, while 40 percent of the food supply is tossed unused every year because of confusion over what the labels actually mean.

While the dilemma of figuring out what we can eat and what needs to go in the trash is quite understandable, staying aware of what’s happening chemically when foods become unfit for eating, both before and after those dates pass, can help us out.

A product’s expiration date can be affected by factory sanitation or the temperature of our refrigerator, but majority of it depends on the type of food we are buying. This is what makes prediction of a product’s real expiration date a bit tricky.

For example, produce may become unfit for consumption an hour after you buy it, or even a week later. This is a huge variation most labels can’t explain. And this happens because of mold, and not because of those brown spots, which are harmless.

Mold targets dead and decaying materials, and you’ve probably seen it appearing on the food that’s going bad or about to go bad in your pantry or refrigerator. Mold can start to grow as soon as 24 hours, and it grows even faster in warm temperatures.

Also, mold is a great substitute for a certain type of cheese, but you do not ever want to eat mold because they can actually hurt you. Some molds produce harmful substances called mycotoxins that if ingested can cause mild to severe health problems which include skin infections, internal bleeding and even death.

Produce is a pretty easy target for molds because it’s rich in water and nutrients, and there are some produces that can’t even hold off the slightest mold penetration.

Well, extending the shelf life of fruits and vegetables is easy. You just have to put them in the fridge.

Cold temperature slows down chemical reaction. While dropping the temperature is a great way to hamper mold growth and reproduction, it will grow eventually. So when this happens, it’s time to throw your produce in the trash.

Also, if you really want to ward off the expiration dates, you’d need to kill bacteria before they start reproducing. Well, this may not be easy with produce, but that’s how milk is treated.

Label says milk is best consumed within two weeks after you buy it, but it could really expire after a few days or even earlier depending on the type and how you treat it.

You are probably familiar with the term pasteurization, where food is exposed to high temperature to destroy harmful microorganisms and denature enzymes that spoils food.

Traditional milk goes through this process. And while it does a good job, it’s not perfect. Some bacteria can survive pasteurization, and eventually they convert sugars present in milk into lactic acid. This explains why spoiled milk has that horrible, sour smell.

The expiration date of pasteurized milk is usually four to six days after you buy it. And considering few days of processing and shipping ahead of reaching the retailers, the shelf life of milk after pasteurization should be around two weeks. However, if the milk gets exposed to warmer temperatures, it may spoil earlier than the Sell-By date.

Drinking spoiled milk won’t kill you but, it will probably give you some brutal food poisoning. And, because you’re smart – you’ll just give it a whiff and probably tossed it away if it bears that lactic acid smell.

Heat treatment processes are good ways for preserving milk, but for meat, you’ll need a different approach.

Meat is an ideal breeding ground for bacteria because it’s wet and laden with nutrients. So, although ‘Sell By,’ ‘Best Before’ And ‘Use By’ dates on it is for a week or so after purchase, and often safe past the labels, it can’t last that long. Also, for the first few days, the bacteria won’t cause any sort of trouble because only few of them are present. But over time, the number will increase. And that’s when the trouble starts.

Bacteria, like Psuedomonas or Lactobacilli, reigns the meat because of the presence of free-floating sugar molecules and light weight compounds on the surface. These bacteria can make you sick, but their presence is easily detectable because they leave behind some foul-smelling end products as they break down sugar and those compounds. These end products are volatile organic compounds, or VOCs, and they smell like rotten meat.

VOCs are an indication that the meat has expired. Also, you can probably tell if the meat has gone bad based on how it looks. VOCs like hydrogen sulfide can make the meat appear green by transforming the muscle pigments.

Labels aren’t always accurate. So regardless of what it says on the labels, if the food stinks or appears unusual, it’s time to let it go.

The table below (courtesy of Mold Guide) tells us how long it takes for foods to go bad when put in the pantry, refrigerator and freezer.

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References And Further Readings:

Monte Carlo simulation of the shelf life of pasteurized milk as affected by temperature and initial concentration of spoilage organisms [FAO]

Role of phenolics in the resistance mechanisms of plants against fungal pathogens and insects [Transworld Research Network]

Changes in the Spoilage-Related Microbiota of Beef during Refrigerated Storage under Different Packaging Conditions
[Applied and Environmental Micobiology]

Cold adaptation in Arctic and Antarctic fungi [New Phytologist]

[Food Product Dating]

Food Storage Chart for Cupboard/Pantry, Refrigerator and Freezer [University of Nebraska – Lincoln]

Function of polyphenol oxidase in higher plants [Wiley]

Why does organic milk last so much longer than regular milk? [Scientific American]

[Video via SciShow]