How can you tell if corn syrup has gone bad?

Corn syrup is a popular sweetener used in many foods and beverages. It’s made from corn starch and contains no artificial ingredients. Corn syrup has an indefinite shelf life if stored properly, but there are signs you can look for to determine if it has gone bad. This article will examine how to tell if corn syrup has expired or spoiled.

What is Corn Syrup?

Corn syrup is a thick, gooey liquid sweetener made from corn starch. The starch is broken down into glucose syrup through an enzymatic process. There are different varieties of corn syrup available:

  • Light corn syrup is pure glucose syrup.
  • Dark corn syrup contains added caramel color and flavor.
  • High fructose corn syrup has some glucose converted to fructose, making it sweeter.

Corn syrup is about 30% less sweet than sugar. It’s used for its viscosity, moisture retention, and crystallization prevention. Common uses for corn syrup include:

  • Candy production – Keeps candy soft and chewy.
  • Canned fruits – Helps fruit retain shape and moisture.
  • Baked goods – Adds moisture and texture.
  • Glazes and frostings – Prevents crystallization.
  • Jams and jellies – Adds thickness.
  • Soda and juice – Adds body and sweetness.

Compared to white sugar, corn syrup has a more subtle sweetness, thicker consistency, and inhibits crystallization. This makes it an ideal ingredient for creating smooth, glossy finishes on foods.

How Long Does Corn Syrup Last?

An unopened container of corn syrup has an extremely long shelf life. The high sugar content prevents microbial growth. Corn syrup lasts for:

  • Unopened – Indefinitely;
  • Opened – About 1 to 2 years.

Once opened, corn syrup absorbs moisture from the air which can eventually cause it to spoil. Keeping the lid tightly sealed helps prolong its shelf life. Refrigeration also helps extend the shelf life once opened.

Properly stored corn syrup does not spoil, but its quality degrades over time. Old corn syrup may not have the flavor vibrancy of a fresh product. It also becomes thicker and darker during storage.

Signs Corn Syrup Has Gone Bad

Because of its high sugar content, corn syrup does not spoil easily. But there are a few signs that indicate it may have gone bad:


  • Cloudiness or precipitation – Fresh corn syrup should have a clear, thick, glossy appearance. Cloudiness, haziness or particles settling on the bottom signify contamination.
  • Darkening color – Over time, the color of corn syrup deepens. If it becomes much darker than the original shade, it could be oxidized.
  • Crystallization – Corn syrup crystallizing into clumps or grains means the sugars have separated.
  • Mold – The presence of fuzzy mold colonies points to spoilage.


  • Thin, watery consistency – Corn syrup should be thick and viscous. If it seems thin and runny, it may have been diluted with water due to improper storage.
  • Grainy texture – Crystallized sugar grains indicate the corn syrup is old and past its prime.

Smell and Taste

  • Fermented odor – The cloying sweet smell of corn syrup will turn sour, indicating the growth of yeast and bacteria.
  • Bitter, burnt, or chemical taste – The flavor profile changes as corn syrup ages.

How to Store Corn Syrup Properly

To get the most life out of your corn syrup and avoid spoilage, follow these storage tips:

  • Keep corn syrup in an airtight container in a cool, dark cabinet away from direct sunlight and heat sources.
  • Refrigeration can extend the shelf life of opened corn syrup for up to 1 year.
  • Ensure opened containers are tightly sealed to prevent moisture absorption.
  • Always use clean utensils when removing corn syrup from the container.
  • Do not store corn syrup in the freezer as this will cause it to crystallize.
  • Keep corn syrup away from heat and humidity.

Can You Save Spoiled Corn Syrup?

Unfortunately, corn syrup that has gone bad cannot be saved. Signs of spoilage mean contaminants have altered the quality of the syrup in ways that cannot be reversed.

Do Not Use Spoiled Corn Syrup If It Has:

  • Mold – Mold spores throughout can make you sick.
  • Foul smell – Bacteria have multiplied, creating toxic byproducts.
  • Crystallized – Sugar separation is irreversible.

Safe Uses for Slightly Degraded Corn Syrup:

If the corn syrup has only darkened or thickened slightly, it may still be usable for non-food purposes like:

  • Craft glue or slime
  • Homemade modeling clay
  • Science projects

But refrain from consuming corn syrup that has changed in appearance, aroma, flavor or texture.

Substitutes for Corn Syrup

If you need to replace corn syrup that has expired or spoiled, here are some suitable stand-ins:

For Baking:

  • Honey – Replace 1 cup corn syrup with 1 cup honey. Reduce liquids by 3-4 tablespoons since honey is wetter. Lowers crystallization.
  • Maple syrup – Use equal amounts. Will add distinct flavor.
  • Granulated sugar and water – Boil 1 cup sugar with 1/4 cup water until dissolved. Cools to a syrupy consistency.

For Canning and Freezing:

  • Glycerin – Use equal amounts. Add slowly as glycerin is very thick.
  • White Karo syrup – Nearly identical to pure light corn syrup.

For Glazes and Sauces:

  • Brown rice syrup – Replace 1:1 cup for cup. Milder in flavor.
  • Agave nectar – Substitute 1 cup corn syrup for 3/4 cup agave. Sweeter so reduce other sugars.

Corn syrup substitutes won’t have exactly the same properties, so expect slight variations in the final product. Test small batches first to adjust other ingredients and achieve preferred results.

How to Tell if High Fructose Corn Syrup (HFCS) Has Gone Bad

High fructose corn syrup is a liquid sweetener similar to corn syrup, but about 20% sweeter. Here’s how to evaluate if HFCS has spoiled:


  • Crystallization – HFCS crystallizing into clumps indicates deterioration.
  • Cloudiness – Particle formation leads to a hazy appearance.
  • Mold growth – Presence of fuzzy mold is a sign of spoilage.


  • Syrup seems thin and watery rather than thick and viscous.

Smell and Taste

  • Fermented, sour odor
  • Odd medicinal smell
  • Soapy, chemical taste

Discard HFCS if any changes in appearance, aroma or flavor are noticed. The same storage tips apply: keep in a tightly sealed container in a cool, dry place. Refrigerate after opening and use within 1 year.

Key Takeaways

  • Properly stored, unopened corn syrup lasts indefinitely.
  • Opened corn syrup keeps for 1-2 years stored in a cool, dark place.
  • Refrigeration extends the shelf life of opened corn syrup.
  • Signs of spoiled corn syrup include crystallization, mold, cloudiness, darkened color, sour smell and an odd taste.
  • Do not consume corn syrup that smells or looks spoiled – discard it.
  • Substitute honey, maple syrup, sugar syrup or glycerin for corn syrup in recipes.
  • High fructose corn syrup spoilage exhibits similar changes in appearance, texture and smell.

The Bottom Line

Corn syrup has a very long shelf life, but eventually goes bad. Examine opened bottles for any mold, crystals, thinning, separation, or foul odors. Discard corn syrup that has spoiled. With proper storage and handling, corn syrup can be kept fresh for 1-2 years after opening. Substitute honey, agave, or pureed fruit if your corn syrup has expired. When in doubt, remember this rule of thumb: if it looks or smells funky, throw it out!

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