Usually, the most important determinant of shelf life is the amount of ‘free’ or ‘available’ water (AW) in the ganache. If there is too much water, it can lead to separation of the fats and provide an environment for mould growth.

Water Activity (AW) is defined as the vapour pressure of water divided by that of pure water at the same temperature. In effect, it is a measure of the ‘free’ or ‘un-bonded’ water in a food product. The closer the AW is to 1, the more liable the product is to bacterial, fungal or mould growth. Typical AW values are 0.99 for raw meats, 0.95 for bread, 0.85 for cheese, 0.6 for dried fruit and 0.3 for biscuits. Solid chocolate has a very low AW and is therefore microbiologically stable. Bacteria usually require an AW of above 0.9 and most moulds require an AW of above 0.8. An AW of below 0.6 would prevent any microbiological spoilage at all and this is what is required if you want a 12-month shelf life at room temperature for your ganache. To lower AW, you need either to remove water, or bind it using agents such as sugars, or lower the temperature of the product.

One common way of reducing the AW of your chocolate centres is to add sugars. There are many sugars that can be added; glucose and sorbitol are the most common. Each sugar has different characteristics and differing levels of sweetness, so you may need to use a combination of sugars to achieve the best overall results. For instance, sorbitol is very good at binding the water and it is only half as sweet as normal sugar (sucrose), but too much can have a laxative effect!