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I make and keep simple syrup on hand to use in my coffee.

Sometimes I will finish it fast enough but other times it starts growing mold before I have used it all up.

This guide that gets referenced a lot on other food channels recommends using 1 ounce of sodium Benzoate per gallon of syrup. (Alongside citric acid) https://www.snowizard.com/content/files/pdf/Literature/Simple_Syrup.pdf

That is 1 part sodium Benzoate per 128 parts syrup. Which is about 0.78% of sodium Benzoate.

However, the US Food and Drug Administration says that there shouldn’t be more than 0.1% of sodium Benzoate in foods. https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/cfrsearch.cfm?fr=184.1733

Does 0.1% of sodium Benzoate have any meaningful effect on the life of the simple syrup?

So I’m not sure which guideline to follow in order to preserve my syrup that I can leave on my counter to add to my coffee and other beverages.

Do you make syrups at home and use preservatives? What would you do?

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  • This similar question may be helpful for you cooking.stackexchange.com/questions/14855/… Oct 27, 2022 at 15:31
  • Does it have to be a simple syrup? If you’re looking for something that will mix into liquid easily, you might want to consider heavy syrup (2 parts sugar to 1 part water) which has less water available for microbial growth
    – Joe
    Oct 28, 2022 at 1:35
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    It may be almost 0.8% sodium benzoate in the simple syrup, but you're not drinking that neat - you're mixing it in your coffee. How much simple syrup in a cup of coffee? You'll be way below the 0.1% level once it's mixed in.
    – brhans
    Oct 28, 2022 at 13:18
  • A bit of potassium sorbate along with a bit of acid (citric?) should suppress mold. Will try this on my next batch of simple syrup.
    – Rob Lewis
    Jul 28, 2023 at 6:02

4 Answers 4

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Simple syrup is, well, simple. As such, what I actually do when using it - make less, and keep it in the fridge. Dry sugar does not generally mold, so keeping the amount that's wet reasonable .vs. the rate of use keeps mold at bay. And sometimes I put in a bit of citric or tartaric acid when making it, in hopes of catalyzing sucrose into glucose + fructose and eking out a bit more sweet for the same sugar.

I'm not clear on why you prefer room temperature storage; I don't have any issue with it crystalizing in the fridge, for instance. Even smaller amounts would be indicated for room temperature storage, though.

If you have some desire I really don't understand to make vast amounts at once, stored at room temperature, then canning is the obvious method, using small jars.

As for sodium benzoate (E211) - don't own any, don't expect to own any.

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If you don't mind a small amount of alcohol in your simple syrup, you can add vodka to inhibit the growth of mould.

I use roughly 30mL of vodka per 250mL of simple syrup — use more or less to taste. I use simple syrup almost exclusively for cocktails, so the small amount of alcohol doesn't matter.

Also note that you can easily make small quantities, so you don't have to worry about it going off: don't boil water to dissolve sugar, just put equal amounts of sugar and water (by weight) into a jar and shake it for a few minutes. Once the fine bubbles clear, the sugar will have dissolved entirely and your simple syrup will be immediately ready for use without needing to wait for it to cool down.

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That SnoWizard link refers to their specific products. Their products are an aqueous solution of Sodium Benzoate (a salt) - but SnoWizard does not tell you the concentration of that solution.

SnoWizard has their concentration of Sodium Benzoate in their product while others use a different concentration (presumably, I cannot find datasheets on any of the products). For example, Hypothermias Sodium Benzoate suggests 1/4 oz of Sodium Benzoate to 1/2 oz Citric Acid, which is pretty different from SnoWizard's instructions. See here.

The FDA Regulation regarding Sodium Benzoate (21 C.F.R. 184.1733) restricts usage to "a maximum level of 0.1 percent in food."

If you want to add Sodium Benzoate to your Simple Syrup, and you want to ensure you are below the FDA set maximum, you could either:

  1. Call SnoWizard and ask what the Sodium Benzoate concentration is in their product, then do some math with those numbers; or
  2. Order Food-Grade powdered Sodium Benzoate and do math to figure out how much you need to add to your syrup. Looking at a few papers, I would guess that concentrations around 0.05% would be an adequate range. See, e.g., A comparative study of the effects of the two preservatives, sodium benzoate and potassium sorbate on Aspergillus niger and Penicillium notatum or Sodium Benzoate and Potassium Sorbate Preservatives in Juices and Fruits[pdf].

This publication suggests 50g Sodium Benzoate powder with 1ml Cherry flavoring and 999mL of Simple Syrup (thereby resulting in ~0.05%).

For further reference: Here is the Scientific Committee on Consumer Products Opinion on Benzoic Acid and Sodium Benzoate[pdf]

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Copper cup?

Note: We have a separate question on whether this is safe, Is copper safe for long-term food storage?.

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Bust out your Moscow Mule mug and keep your syrup in that. Mold is exquisitely sensitive to copper. The amount that leaches into the syrup will prevent mold growth, I here assert.


I am back, with some science. Especially for you, @Esther because you doubted and you were right to doubt. This premise is testable experimentally and that is what I did.

jar setup

Here is the setup as of 11/2 - 1 week ago. I made the sugar syrup with a 1:1 sugar and water mix, heated in a saucepan. Jars were rinsed first. Approximately 150 ml syrup in each of 8 jars. I did not have a copper cup but I had a silver one - also 150 ml.

To simulate a copper metal cup I used pennies. These are American pennies which I washed with dishsoap and rinsed. First 2 jars (0) were controls with only syrup, no pennies. Subsequent jars had 2 pennies (x2 jars), then 5, 10, 20 and 30 pennies.

Experiment is ongoing. Here are results as of this AM 11/9 at 1 week.

no penny1

nopenny 2

Jars with only syrup and no pennies had mold colonies by day 3 and they are easy to see now. The mold looks like aspergillus (bread mold) and is floating on top.

2 pennies

Jars with 2 pennies had a few mold colonies.

5 pennies

Jar with 5 pennies developed mold for the first time this morning. I put red arrows on the mold colonies.

Jars with 10,20 and 30 pennies have no mold colonies yet. Neither does the silver cup. below: 10 and 20 penny cups (30 pennies not shown) and silver cup.

10 pennies

20 pennies

silver cup

For sugar syrup left open at room temperature. addition of metal as copper or silver retarded mold growth over the experimental period of 1 week.

You could do this now as pennies. Or maybe a piece of scrap copper pipe from your shop? A classier way would be to get a little silver creamer pitcher which would both retard mold as my silver cup did and be easy to pour from into your coffee.

The most vexing thing now is how to get people to revisit this question (now invisible from the downvotes) and replace those heartrending downvotes with sweet smelling upvotes!

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    I like so much about this answer. It is unexpected, non-confrontational, but provably (and proven) correct. Nov 9, 2022 at 16:54
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    This seems like a bad idea. Copper is toxic in large quantities, and copper from storage containers will leech into your simple syrup over time. On the other hand, this paper suggests that storing water in copper containers is a good idea, though keep in mind that the goal of this study was to determine if short-term storage of drinking water in copper vessels was useful as an anti-microbial treatment. Long term storage seems ill-advised to me. Dec 8, 2022 at 23:42
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    @Willk The US FDA advises against using copper implements with acidic foods, as copper can be leeched into a mildly acidic solution pretty quickly: fda.gov/media/110822/download (p. 115; p. 488-9). Simple syrup should be pretty close to neutral (depending on local tap water), but we are also talking about storing a simple syrup solution for long periods of time. Like I said, it seems like a bad idea to me. Dec 9, 2022 at 2:22
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    The safety issue here is really important, and the best way to sort it out is probably to ask a separate question rather than continue a discussion in comments.
    – Cascabel
    Dec 9, 2022 at 2:30
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