Managing Mould

If maple syrup is not hot packed correctly or property stored after opening, mould can grow on the surface. This mould is caused by spores of fungi, yeasts and occasionally bacteria. Together, these fungi, yeasts, and bacteria are called “spoilage organisms”. Spoilage organisms are a fact of nature and are in constant interaction with organic matter, soil and moisture in our environment.

The presence of mould in maple syrup can have a major negative impact on the perceived quality of the product.

A closeup of a glass bottle of maple syrup. White mold is on top of it.

Preventing spoilage mould from developing in maple syrup retail containers can be a challenge for many maple syrup producers.

How to Prevent Mould

Hot packing is the most common mould prevention strategy. Hot packing is done for both retail and bulk containers that will be used for long-term storage. Cold-packing maple syrup typically results in mould growth, which can pass on off-flavours in the syrup. 

Closeup of a glass bottle filled with maple syrup. A red circle highlights the air between the syrup and the bottle cap, and a caption indicates that this is a high-mold risk area.
The air space between the product and the lid is known as the “head space”.

How to hot pack:

  1. For retail sales, use only brand new, clean containers that have been kept in a clean and dry storage room

    Be ready to hot pack immediately after filtering.

    Do not use containers or lids that cannot tolerate temperatures of 82-85⁰C (180-185⁰F).

    Increasing the syrup temperature above 90⁰C (194⁰F) can cause new sugar sand (niter) to form and require filtering again.
Plastic milk jugs filled with maple syrup.

Please note: Containers that are commonly used for fresh milk are not designed for hot packing temperatures for maple syrup. Using these for maple syrup is discouraged by the provincial industry for retail sales.

2. Pre-heat all glass retail containers, or they will cool down too quickly to provide adequate sterilization

A hot water bath or a warm oven are good pre-heating methods (if using a hot water bath, keep the cap above water level).

Plastic and tin retail containers may not require pre-heating.

3 small glass bottles of different shapes and sizes. One is filled with maple syrup.
Small containers are particularly susceptible to mould growth, as there is not enough syrup to keep the bottle hot for the length of time needed to provide adequate sterilization. Pre-heating is required.

3. Fill bottles.

Maintain syrup temperature at 82-85⁰C (179-185°F) during filling

Fill retail containers to at least 90% of container volume (Regulatory requirement under O. Reg. 119/11).

Use protective gloves made of silicon or heavy-duty rubber for a better grip on preheated bottles while filling.

Four photos of a line of maple syrup bottles being progressively filled with syrup.
Two photos of an automatic bottler with rubber gaskets. The caption says "modern maple syrup bottling equipment is made of food grade material and is designed to be easy to clean and sanitize. During filling with hot syrup, bottles are sesasled by a gasket, which helps prevent airborne spores of fungi or yeast from contaminating the container and syrup."

4. Secure new clean caps

5. Immediately turn hot bottles upside down for 3-5 minutes to heat inner cap, head space, and neck

A hand turning a bottle full of maple syrup upside down.
  • After flipping the bottle upside down, the neck and inner lid are treated with hot syrup
    • Any airspace will fill with water vapour, which condenses to liquid water on the inner walls as it cools
    • Surviving organisms can continue to grow in this water + low sugar environment
    • Any condensed water in the air space will mix back into sugary syrup
    • Some producers use the cardboard box the bottle came in to hold the flipped bottles  

6. Turn containers upright and let them cool quickly to stop the cooking process

Spread the containers out on a table in a cool area; use a fan to speed cooling.

Never immerse hot glass containers in cold water! This could cause glass to shatter.

As hot packed maple syrup begins to cool, it contracts and creates a vacuum in the head space of properly sealed container.

The resulting container environment is oxygen-free which makes it unsuitable for mould growth.

A bottle of full maple syrup with white mold growing on top. Captions say: "unopened in the pantry, spoilage mold developed within 2 to 3 weeks after purchase. Due to a problem during hot packing, didn't preheat hte glass, didn't invert the container after hot filling, syrup not hot enough, cap not secured. Density = 68.5 degrees Brix mold can still grow.

7. Check the headspace for any condensed water

If there is any, invert container again to force it back into the syrup

If mould is a reoccurring problem after hot packing, don’t hesitate to ask for assistance from an experienced maple syrup producer, food inspector, maple extension specialist, equipment dealer or other maple industry professionals.

Best Practices to Prevent Mold Throughout Post-Boil

Making maple syrup by exposing raw sap to boiling heat will kill the most common spoilage organisms. However, some heat-resistant mould spore populations are capable of surviving temperatures higher than 82 °C (179°F). Hot packing does not guarantee destruction of all mould spores. 

Spoilage organisms can also re-enter into maple syrup at several access points during post-boil handling. Points of contamination include:

  • during and after filtering
  • loading bulk containers
  • transferring syrup through hoses or pipes into bottling tanks
  • filling retail containers

Follow these best practices to reduce the likelihood of mould formation:

Before Boil
  • Spoilage spores can be present on container surfaces, equipment, on the floor, in drains, on our clothing and floating freely in the surrounding air
  • Use good cleaning and sanitation practices through all steps in maple syrup production, especially the packaging environment.
  • Clean and sanitize all tig-welded stainless steel pans, steam hoods, vents, smokestack, valves and fittings
  • Tig-welded stainless steel drums are cleaned, sanitized and rinsed with potable water in preparation to store bulk maple syrup
During Boil
  • Ensure that maple syrup is concentrated to the correct minimum density/sugar concentration of 66.0 ⁰Brix
    • The ideal density is 66.5⁰ Brix to 67.5⁰ Brix for best quality and ‘mouth feel’
    • Syrup density should not be higher than 68.9⁰ Brix to prevent crystallization of sucrose sugar in the syrup
Bottle Filling
A photo of a rectangular metal container with spouts and valves protruding from it, used to bottle maple syrup. The caption says: "a homemade bottling station can work for hot-packing maple syrup. Extra care will be needed to ensure the bottling area is in a clean and sanitized condition. For example, wood surfaces or gaps between teh bench frame, countertop adn the syrup tank may be difficult to keep sanitized from mould spores near the open bottles during filling.

Wear safety equipment:

  • heat-protective mitts or silicone gloves to protect hands from burns
  • arm, eye, and face coverings to protect from splashing hot syrup
  • clean clothing and footwear
  • hairnet or clean hat
  • Use a storage area that has few temperature fluctuations
  • If you are unable to hot pack, keep bulk and retail syrup in the freezer
    • Storing at 1 to 3 ⁰C (32 to 38 ⁰F) is ideal to preserve quality
    • A freezer will preserve maple syrup quality for several years
  • Designate a room for storing new retail containers, lids, and other supplies
    • Keep room clean, dry, and orderly
    • Trap all mice
  • Steel storage containers can be adapted for this purpose, or can add lockable security and additional storage space outside of the sugar house
  • Do not store chemical cleaners, sanitizers, and pesticide products with food manufacturing supplies
  • Always refrigerate opened bottles of maple syrup
One photo of a storage room with boxes piled along the sides, another of a portable blue storage container with boxes inside.

What if I find mould?

When mould in syrup is found, it is best to throw out the syrup. Mouldy syrup can be placed in the garbage, buried if the ground isn’t frozen, or thoroughly mixed into to an active, contained composter of decomposing organic material that is located a reasonable distance away from the sugar house and sap collection areas.

Consumers can react emotionally with disappointment, annoyance or anger at the appearance of mould in their food, often evaluating the product against the money they have spent.  A low percentage of people can experience allergic reactions to specific mould spores.  The presence of spoilage, in this case mould in maple syrup, can create doubt about safety and quality.

Basically, use good common sense and accept it as lost product. Keep your customers happy and coming back for more of your quality maple syrup.