How long can you store simple syrup?

Question

I have a 2:1 (2 parts sugar, 1 part water) simple syrup by mass that I use for cocktails. How long can this last? Or, in other words: when should I discard it? In one bar I know they would discard the syrup if it was one week old, but that syrup was 1:1 ratio.

To my understanding one can prolong the storage-liftime by adding somethig acidic? But, I am a little relunctant to do this as it may mess with the taste and/ or balance of the cocktails.

(The 2:1 syrup doesn't mess with the balance because if the recipe uses 1:1 I can just calculate the equivalent amount of 2:1 syrup that would use the same mass of sugar and add water to get the same volume and dilution. Example: recipe says 20mL of 1:1 syrup, I calculate that I need XmL of 2:1 syrup to get the same mass of sugar in the syrup, and then add (20-X)mL water.)

Do I switch it out when I see that it begins to crystallize? When should I make a new batch and switch it out? I once had a 1:1 that I shelved for too long (several months) and there was something green or turquoise floating in it (mold or bacteria?). I have stored the 2:1 for several months and it seems fine, but it crystallized somewhat. Is it bad that the simple syrup crystallizes?

Answer 1

I'm not sure if the other questions have a direct answer to your question, so I'll put one here.

I can say from personal experience that you can keep a 2:1 simple syrup in a sealed container in the fridge for months to years. It has to be sealed primarily to prevent evaporation, because you don't need to go far beyond 2:1 for the sugar to crystallize. Theoretically, adding some invert sugar would increase the level of saturation without crystallization, but I don't have direct experience or data for that.

Outside the fridge, I'd be concerned about fermentation, particularly if you're opening the syrup regularly to use it.

Crystalization isn't a problem, beyond that you're losing some of the sugar out of the syrup, and eventually it becomes not pourable. However, nothing stops you from re-heating the syrup to dissolve the crystals and adding a tiny bit of water.

Mold is a problem, potentially. The syrup might be OK if you just skim the mold, but it might not, and simple syrup is pretty cheap. Why take a chance.

Answer 2

It should be noted that a 2:1 (sucrose:water, AKA 200% solution) solution is saturated at room temperature, this means you won't be able to add any additional sugar or lose any water without crystals forming. Low temperature might well also induce crystal formation as the solubility of sucrose depends on temperature. See the Engineering Toolbox for the solubility curves.

From a food safety perspective, the water activity (Aw) of a 200% sucrose solution is 0.86 (PDF). This is below the limit for growth for most common pathogenic bacterial species, apart from Staphylococcus aureus, which will grow at Aw of 0.86, but not below the Aw of most molds, which grow down to about 0.80. Most yeasts are inhibited by Aw of 0.88, though there are some that will grow at lower Aw, but I don't know how common these would be in a kitchen setting.

This means, that you should be able to store this solution in the fridge almost indefinitely, just make sure that you prepare it in a clean environment and are putting it into a clean and sterile container for storage. A sterile container might be one that has been dry baked in an oven at about 200 C (390 F), much as you would for preparing jams/jellies.

You should keep an eye out for molds and discard if these are observed. The more times you go into the solution, the greater the risk of contamination, so best to keep in volumes that you might use within a few (<20?) uses.