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Today I discovered a 1/4-full bottle of pure maple syrup had gotten moldy, so searched this site and came across this question: Should maple syrup be stored in the refrigerator?

My follow-up question is: Will there be any ill effects (such as altering the flavor or changing the molecular structure such that it's dangerous to eat, etc) from repeatedly heating maple syrup for serving, and re-cooling in the fridge?

If so, I'll try to only heat as much syrup as I'm likely to use at a time, although this will be more hassle, naturally :)

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It behaves similar to honey, with the sugars (which are more than 95%) not changing, but the rest (which gives all the aroma) may change. See cooking.stackexchange.com/questions/13162/… –  rumtscho Sep 21 '11 at 9:34
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4 Answers

up vote 2 down vote accepted

Flimzy,

If you use a lot of maple syrup, you won't need to refrigerate it; it'll keep at room temperature (depending on the temperature of your room) for a few weeks.

Repeated heating and cooling, in my long experience with pure maple syrup at home, does not affect the flavor or color of the syrup. This makes sense when you realize that maple syrup is boiled for hours in its manufacture.

However, it can cause the syrup to crystallize, and I haven't found a good easy way to decrystallize syrup (the hard way is dissolving it in water and boiling it down again). For this reason, I only heat up the amount of syrup I intend to use at a time.

I am not a food safety expert; I'm just speaking from my experience at home.

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Clearly I don't go through it fast enough to keep it from molding. :) That's interesting about it crystallizing... that's probably good enough reason to only heat as much as I need at a given time. –  Flimzy Sep 22 '11 at 5:20
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The Cornell Sugar Maple research program website has a couple of relevant points:

If you find mold inside a newly-bought, previously unopened bottle of syrup, it is probably spoiled because of improper packaging.

What causes syrup to have a musty or moldy flavor or smell? Syrup that is improperly packed will mold, sour, or ferment. Syrup must be packed at 180°F and at a minimum of 66 Brix to avoid spoilage.

(Brix is the measure of sugar in the syrup.)

In your particular case where you see mold and want to reheat it, it seems that yes, you can reheat the syrup but it may crystallize a little:

If a consumer finds bacteria, mold, or yeast growth on syrup he or she has purchased, he or she should remove the visible growth and reheat the syrup to a minimum of 180°F (do not boil), skim any visible growth, filter, and repackage the syrup. If syrup still has an off-flavor, it should be discarded. Also, the sugar content may increase causing sugar crystals to form.

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So I guess the implication then is that re-heating the syrup to 180°F multiple times won't harm the syrup in any way. –  Flimzy Sep 21 '11 at 18:14
    
@Flimzy that's my understanding as well. –  Laura Sep 21 '11 at 21:37
    
It also sounds like the issue with crystallization could be avoided if the syrup were diluted to give it the same volume as it had before reheating. –  Theodore Murdock Aug 28 '12 at 19:43
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Going off of what Laura said, no, heating the maple syrup multiple times won't cause any change in the structure of the syrup, but do refrigerate the syrup after your done if it says so on the bottle.

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My bottle doesn't say to refrigerate, but it still grew mold. :) It does say "no preservatives", though... –  Flimzy Sep 21 '11 at 18:56
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If it's actual maple syrup (not imitation syrup) and it doesn't have preservatives, it should be refrigerated. –  Laura Sep 21 '11 at 21:37
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I produce maple syrup from the sugar maples on my property. I make about 8 gallons a year, so not a huge commercial endeavor. This past year, several quart jars of our syrup grew a powdery grey mold. I processed the syrup until it reached the 219F and 67% sugar, as measured with a hydrometer. Many jars grew sugar crystals, indicating high enough sugar content. I cleaned and sanitized the jars and lids with care, as we always do. When canning - the syrup reached 180F and was then put in the sterile jars, and lids applied. Today, I reheated the syrup to the boiling point to be absolutely sure it is sterile - and also sterilized the jars in a pot of boiling water. I'm sure to grow sugar crystals again, but I'm just hoping the 3 gallons of syrup I recanned still taste alright.

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So am I correct in understanding that your recommendation is to remove the mold, then sanitize the syrup again with heat? –  Flimzy Aug 26 '12 at 21:10
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