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 / Updated  / Source: TODAY
By Madelyn Fernstrom

Buying in bulk sounds like a good idea until you check out your pantry and fridge and find foods that are labeled "best by" many weeks ago. And what about multiple bottle of salad dressing that have been opened for months?

Read on for decoding the shelf life of some of our favorite liquid foods.

In your pantry (unopened foods):

Shelf-stable boxed milk—purchased 5 months ago

KEEP

Samantha Okazaki / TODAY

Because this milk is ultra-pasteurized, it's shelf stable at room temperature for about 6 months. After it's opened, store in the refrigerator where it will remain fresh for about a week.

Beer— purchased 6 months ago

TOSS

Samantha Okazaki / TODAY

While this beer remains safe to drink when unopened, you can expect some changes in taste and after around 4 months

Diet soda—"best by" two months ago

KEEP

Samantha Okazaki / TODAY

Even unopened, diet sodas don't maintain optimal taste and flavor indefinitely. The combination of low-calorie sweeteners used in most diet sodas start breaking down after about 3 months past the "best by" date, accompanied with major changes in expected taste and flavor. So, until then, it's a keeper.

100% fruit juice box — purchased 10 months ago

TOSS

While it seemed like a good idea to stock up on the juice box sale, after around 7-8 months in your pantry, you'll likely lose flavor, with some decline in nutrients (like vitamin C). It's still safe to drink. And once opened, the juice is okay to drink for about 7 to 10 days.

Bottled Water — purchased 1 year ago

KEEP

Bottled water has a shelf life of about 2 years, without any change in taste. It's important to avoid storing the bottled water exposed to direct sunlight, or in a very warm pantry as it is possible to have an interaction of the plastic bottle components with the water.

In your fridge (opened foods):

Chocolate syrup — opened 6 months ago

KEEP

Samantha Okazaki / TODAY

That bottle of chocolate syrup that's been in your fridge for months remains safe and tasty for up to a year after opening. An unopened bottle will remain stable in your pantry for at least one year after purchase.

Balsamic Vinaigrette Salad Dressing — opened 6 months ago

TOSS

Samantha Okazaki / TODAY

If you're looking for optimal taste and flavor, toss your opened bottled salad dressings around 4 months after opening. This applies to oil-based dressings; for milk and cheese based dressings, once opened, it's about a month.

Evaporated milk (can) — opened 1 week ago

TOSS

While a can of evaporated milk will be stable up to about 9 months past the "best by" date, once opened it's only stable for about 3-4 days.

Liquid coffee creamer opened 21 days ago

TOSS

Once opened, a container of liquid creamer is good for at least 2 weeks. But depending on how it's been stored in between use will impact how long it's remains fresh; left out at room temperature for several hours on multiple days, for example, might shorten the days of freshness.

100% Maple syrup - opened 6 months ago

KEEP

Samantha Okazaki / TODAY

Pure maple syrup maintains optimal flavor and taste for around 1 year after opening. 100% maple syrup (with no preservatives) must be stored in the fridge to sustain freshness, in contrast to syrup blends which often have a label instructing "no refrigeration needed."

Madelyn Fernstrom is health and nutrition editor for NBC News and TODAY. Follow her at @drfernstrom.