Syrup Preservation Tips

These are some tips to keep syrups lasting longer without spoiling. These won't render syrup shelf-stable indefinitely, but might help extend the life of spoilable syrups. 

• Increase the sugar level - Higher sugar levels reduce water availability to microorganisms. Bring your sugar level (brix) up to at least 50. That means equal parts sugar and water by weight (not by volume).
• Add alcohol – 15% or so of alcohol helps work as a preservative environment; the higher the better. (Note alcohol at this level will not sterilize the syrup, merely extend its lifespan.)
• Strain syrups well – homogeneous environments are best. Chunks are bad. 
• A Campden tablet kills bacteria and is used to sterilize wine/beer to stop further fermentation.
• Citric acid/vinegar/an acidic environment (low pH) help preserve syrups.
• Bring it to 186 degrees for 6 seconds, or bring it to 140 degrees for 10 minutes. There are charts on how to pasteurize acidified products all over the internet.
• Hot Fill. While the liquid is at least 120 degrees, fill the bottle, cap it and invert it for at least two minutes. As the liquid cools, it shrinks (hot liquids fill more volume than cold liquids), creating some negative pressure .
• Read websites on canning – they know what’s up.
• Make an invert syrup rather than adding sugar to water cold. Invert the syrup by holding at 240 degrees. The addition of a little cream of tartar (or, barring that, a little lemon juice for the citric acid) will help split the sugars to invert.