Why is there mold in my maple syrup?

Maple syrup is a natural sweetener made from the sap of maple trees. While it is enjoyed by many, sometimes mold can develop in opened bottles of maple syrup. There are a few reasons why mold might grow.

Quick Answers

Mold can grow in maple syrup when:

  • The bottle has been open for a long time
  • The syrup wasn’t processed or sterilized properly
  • The bottle wasn’t stored properly after opening

Small amounts of mold are not dangerous, but should be avoided. To prevent mold, store maple syrup in the refrigerator after opening and check for signs of mold before use.

What Causes Mold to Grow in Maple Syrup?

Maple syrup is vulnerable to mold growth because of its chemical composition. The high sugar content provides food for mold spores. Maple syrup also lacks preservatives found in commercial pancake syrups that prevent microbial growth.

There are three main reasons why maple syrup often develops mold:

  1. The bottle has been open for an extended period
  2. The syrup wasn’t processed or sterilized sufficiently
  3. The opened bottle wasn’t stored properly

Long-Opened Bottles

Once a maple syrup bottle is opened, mold spores in the air can get into the syrup. Over time, these spores may germinate and grow, especially if the bottle has been open for many months.

Maple syrup’s high sugar content provides lots of nutrition for mold. Leaving maple syrup open for long periods gives mold spores a chance to use this food source and multiply.

Insufficient Processing

Maple syrup is made by boiling and processing maple sap. This heating kills most microorganisms in the sap. However, if the sap isn’t boiled long enough or hot enough, some mold spores can survive.

Smaller, artisanal maple syrup producers may be more likely to have insufficient processing. The more extensive procedures used by larger commercial operations reduce the risk of mold in unopened bottles.

Improper Storage

To limit microbial growth after opening, maple syrup should be refrigerated. The cold temperature slows mold growth. However, some people store opened maple syrup bottles in the pantry.

Pantry storage allows the bottle to remain warm. This warmth combined with the high sugar content of maple syrup makes an ideal environment for mold development.

Is Maple Syrup Mold Dangerous?

In most cases, a small amount of mold in maple syrup does not pose a serious health risk. The mold commonly found in syrup is primarily a problem due to quality and taste.

However, there are a few potential issues to be aware of:

  • Some people may have mold allergies that cause reactions.
  • Toxins can form as mold grows over time.
  • Mold can indicate spoilage and a poor handling and processing practices.

If you see any mold in an opened maple syrup bottle, it’s best to discard the syrup.

Allergic Reactions

Although rare, some people are allergic to common molds found in foods. Ingesting maple syrup with mold could potentially cause an allergic reaction.

Symptoms might include rash, stuffy nose, irritated eyes, or upset stomach. Severe reactions are unlikely, but people with known mold allergies should be cautious.

Toxic Mold Metabolites

Over time, some types of mold release toxic substances call mycotoxins. As mold growth progresses, the concentration of these metabolites builds up.

In significant amounts, mycotoxins can cause health issues. However, serious toxin accumulation requires extensive, visible mold growth over weeks or months.

Poor Processing and Handling

Finding some mold in maple syrup could indicate a bigger problem with how the syrup was made and packaged. Poor processing may allow mold spores or other microbes to survive.

Dirty bottling conditions can introduce mold into bottles before sealing. Store your syrup in a different location if you notice mold so it doesn’t contaminate other foods.

How to Prevent Maple Syrup Mold

You can prevent mold growth by handling maple syrup properly after opening:

  • Refrigerate opened bottles
  • Keep bottles sealed tight
  • Check for signs of mold before use
  • Clean bottle rims and tops before resealing
  • Store bottles upside down to inhibit oxygen exposure

Refrigerate Opened Bottles

Once opened, maple syrup should always be refrigerated. The cool environment helps prevent microbial growth.

Pasteurized syrup in factory-sealed bottles can be kept at room temperature. But refrigeration is best after opening.

Keep Bottles Sealed Tight

Always seal the maple syrup bottle tightly after each use. Oxygen can promote mold growth.

Replace caps or lids properly to prevent air entry. If using syrup dispensers, make sure the spout seals firmly.

Inspect Syrup Before Use

Check maple syrup bottles for any signs of mold before use – especially if they have been open for over a month.

Look for surface mold, fuzziness, white spots, or strange colors. Discard immediately if mold appears.

Clean Bottles and Caps

Food and moisture around the maple syrup bottle opening provide nutrients for mold. Always clean the rim and cap before sealing.

Wipe the bottle neck and threads with a clean towel before replacing lids. Wash reusable dispenser caps before attaching.

Store Bottles Upside Down

For bottles with narrow openings, flipping them upside down can limit oxygen exposure to the syrup. This helps inhibit mold growth.

However, only store bottles upside down if they have a sealed cap. Leaving them open can cause syrup to leak out.

What To Do if You Find Mold in Maple Syrup

Finding mold in your maple syrup isn’t cause for panic. Follow these steps if mold appears:

  1. Discard the contaminated syrup
  2. Clean the bottle thoroughly before reusing
  3. Inspect your pantry for leaks or contamination
  4. Use fresh syrup and refrigerate after opening

Discard the Contaminated Syrup

Maple syrup with mold growth should not be consumed and should be thrown away. Don’t attempt to skim or scrape off the mold.

Toss out the entire bottle, even if some areas don’t show mold. The spores could have spread throughout the syrup.

Clean Bottles Thoroughly

Before using maple syrup bottles for fresh syrup, wash thoroughly with soap and hot water.

Clean the entire interior surface, not just visible problem areas. This removes any lingering spores.

Inspect the Storage Area

Check around opened syrup bottles for stickiness, drips, or leaks. Clean any syrup residues that could transfer mold to other containers.

Discard any food items near maple syrup bottles that might have mold spores. Sanitize the shelves and surrounding area.

Use Fresh Syrup and Refrigerate

When reusing bottles, fill them with fresh syrup from an unopened container. Immediately refrigerate after opening.

Avoid using syrups that have been stored at room temperature for long periods. Always check for mold before use.

How To Identify Maple Syrup Mold

Maple syrup can develop various types of mold based on environmental conditions and the spores present. Here are some common molds found:

Penicillium Mold

Colonies of fuzzy blue/green mold on the syrup surface are often Penicillium. This genus includes food mold species that grow on sugary, acidic foods.

Cladosporium Mold

Olive green or brownish splotches are typically Cladosporium, a mold often found in refrigerated jams and fruit products due to cooler temperature growth.

Aspergillus Mold

Aspergillus can form woolly green-black mold spots. Some species produce toxin mycotoxins under certain conditions.

Fusarium Mold

Fusarium is a filamentous mold that can cause a white, creamy discoloration. Growth is encouraged by higher sugar and acidity.

Botrytis Mold

Wooly gray fungal growth is characteristic of Botrytis mold. It thrives on sugars and is common on fruit, vegetables, and syrups.

If you see any growth or discoloration that looks suspicious, it’s best to discard the maple syrup to be safe.

Mold Growth Factors in Maple Syrup

Certain characteristics of opened maple syrup make it prone to mold growth. The main factors that contribute to mold development include:

  • Sugar content – provides food for mold
  • Acidity – creates favorable mold conditions
  • Oxygen exposure – introduces mold spores
  • Moisture – promotes mold germination
  • Temperatures – warmer increases mold growth

Sugar Content

Maple syrup gets its sweet flavor from high amounts of sugars, mainly sucrose, glucose, and fructose. These sugars are an ideal food source for molds.

The plentiful sugars allow rapid mold growth. Types of mold that thrive on sugars proliferate easily in maple syrup.


The natural acidity of maple syrup also encourages mold growth. Mold species prefer slightly acidic conditions typically found in products like jams, fruits, and syrups.

The lower pH, around 3.5, provides favorable conditions for microbial growth compared to neutral foods.

Oxygen Exposure

When maple syrup bottles are opened, oxygen can enter and bring in mold spores. Air exchange introduces new mold colonies.

Leaving bottles open or partially resealed allows for repeated oxygen exposure. Tight sealing prevents oxygen introduction.


Microbes need sufficient moisture to grow. Maple syrup’s high moisture content and water activity make it vulnerable to mold.

Drier products like flour limit mold growth. Maple syrup’s wetness provides hydration for rapid mold reproduction.


Warmer temperatures accelerate microbial growth. Storing opened maple syrup bottles in hot pantries quickens mold development.

Refrigeration slows mold growth by cooling bottles below optimal mold temperature ranges. Cold maple syrup lasts longer.

Safe Maple Syrup Storage

Use these safe storage practices to keep opened maple syrup mold-free:

  • Refrigerate opened bottles at 40°F or below
  • Keep bottles tightly sealed in refrigerator
  • Wipe rims and cap before sealing
  • Discard syrup after 1 year in refrigerator
  • Store unopened bottles in cool, dark pantry

Refrigerate Opened Bottles

Always refrigerate opened maple syrup bottles to inhibit microbial growth. The cold temperature inside a refrigerator, around 40°F, slows mold growth.

Never store open maple syrup bottles in the pantry long-term. The higher temperature will lead to rapid mold issues.

Keep Bottles Tightly Sealed

Seal maple syrup bottles completely before refrigerating. Oxygen entry encourages mold growth.

Replace lids tightly and ensure any dispenser spouts are closed. Tight sealing prevents air exchange.

Wipe Bottles Before Sealing

Food and sugars around the bottle rim provide nutrients for mold. Always wipe the bottle opening before sealing.

Use a clean towel or paper towel to remove residues on threads and caps. This prevents mold transfer.

Discard Syrup After 1 Year

Over time, even refrigerated maple syrup loses freshness and mold risk increases. Discard opened bottles after 1 year as a precaution.

Write the opening date on bottles to track age. Syrup older than a year may be unsafe to consume.

Store Unopened Bottles in Pantry

Newly purchased, factory-sealed maple syrup bottles can be kept in a cool, dark pantry before opening.

Avoid warm spots near appliances. Refrigerate after opening the bottles.

Maple Syrup Shelf Life

The shelf life of maple syrup varies based on storage conditions and opening:

Unopened Maple Syrup

  • 2 years shelf life at room temperature
  • 3 years maximum recommended shelf life
  • Discard if mold, separation, or crystallization

Opened Maple Syrup

  • 1 year shelf life refrigerated at 40°F
  • 2 months maximum shelf life in pantry
  • Discard at any sign of mold immediately

For longest shelf life, store new bottles in a cool pantry and refrigerate immediately after opening. Discard older syrup. Unopened, commercially packaged maple syrup lasts about 2-3 years.


Finding mold in your maple syrup can be annoying and concerning. But rest assured, small mold growth generally isn’t hazardous if you discard affected syrup.

To prevent maple syrup mold after opening, make sure to refrigerate bottles and seal them tightly. Check for any mold, moisture, or stickiness before resealing.

Maple syrup’s high sugar content and acidity makes it prone to mold growth. Proper refrigerated storage is key to limiting microbial issues. With safe handling, you can continue enjoying syrup mold-free!

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