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Syrups
This method works to preserve my Orange and Ginger Syrup, and Grenadine.
Stabilizing Syrups
I want to preserve homemade syrups for drinks and baking, so they are shelf-stable for extended periods. These are basically simple syrup with various flavors, or juice syrups.
I found a few guides online, simple and complicated. The best ones for being both rigorous enough to be trusted, and simple enough to be feasible, agree on the approach: to "use up" all free water with other solutes. Different compounds have different potency in this regard, but if the known quantities of preservatives are sufficient, then other dissolved or suspended solids will be preserved.
A best concise summary is here: https://pharmlabs.unc.edu/labs/solutions/preserving.htm.
The Formula Details
A solution in water can be made stable by having all "free water" preserved by a combination of preserving solutes.
- A 65% sugar-water solution, by weight, is shelf stable.
- A 15% ethanol-water solution is shelf stable.
Rubber and Road
My orange, ginger, and grenadine syrups are based on 1:1 volumetric ratios of sugar and water.
Considerations:
- The grenadine is 1:1 with pomegranate juice, plus some molasses and a tiny bit of scented water.
- The ginger and orange peel may add moisture, along with their own oils and solubles.
The orange oils themselves are preservative, as are some ginger solubles, so I'll compute the total volume as water. Because these preservation computations are based on eliminating all "free water", this overestimates our needs and we'll err on the side of caution.
Compute
1c Sugar: 7.72 oz 1c Water: 8.64 oz My 1:1 mixture is actually .89:1 by weight, or 47% sugar, 53% water.
I need to make up the difference in alcohol.
I need a 65:35 sugar:water ratio, but have a 47:53 ratio. The 47% is enough to preserve: x=(47/65)*35 = 25.3% of the total weight, in water. Water is 53% total weight, leaving ~28% total weight as free water.
To preserve that last 28%, we need 15% * 28% = (4.2% * total weight) extra ethanol.
The fact that some of this weight is actually rind, fibers, or juice solutes actually decreases our required preservative - we're overestimating.
Ethanol Add
I'm using 75% grain alcohol, by volume. Ethanol has a 0.78924 g/mL density. Water has a 1.1111 g/mL density.
If this alcohol is 75% by volume, it's (.75 * .79) / ((.75 * .79) + (.25 * 1.11)) by weight, or 68.1%. Leaving 31.9% water by weight. The Everclear's own water requires (31.9% * 15%) of the total weight in alcohol to stabilize, or 4.8%. Leaving us with 63.3% effective alcohol, by weight. To add 1g ethanol, we must add 1.58g Everclear.
1c syrup weighs in at 9.56 oz. To each cup syrup we must add (9.56 oz * .042) = .4 oz ethanol = (.4 oz * 1.58) Everclear = .632 oz Everclear.
1c syrup + .632 oz Everclear (< 2 tbsp) should be shelf stable.
Can somebody test this for me? I'll give you some stabilized syrups, tell me if there's mold next year.
Gotcha!
All this reasoning breaks down with exposed solids. As with pickling and brining, this reasoning only works as long as everything is under the solution. The solids which float and are exposed to air change the equation. Ginger tends to sink. Orange peels tend to float.
It's my opinion that the orange peels, boiled in sugar and containing their own oils, will last for a while. It's also my opinion, based on my experience fermenting alcohol and fermenting in salt water, and reading the internet, that if you can't see it yet, it can't hurt you.
YMMV.