Water activity (AW) in a ganache

A ganache is a stable emulsion consisting of liquid (water) and fat. Most micro-organisms need water to thrive/reproduce and therefore, you want to bind the water in the ganache as much as possible so that the water is thus made inaccessible to the micro-organisms. Be aware of that in relation to ganache, we talk about water activity and available water (AW). Not about the portion of total water per se in the bonbons but about the portion of water that is not bound – and is thus accessible to the micro-organisms. An AW value of 1 means that there is 100% unbound water, while an AW value of 0.5 means that there is 50% unbound water. The lower the AW value, the longer the shelf life.

Water Activity (AW) in a ganache

In a ganache which only consists of cream and chocolate (i.e. no added sugar), the AW value will typically be above 0.90. Therefore, the shelf life of a chocolate bonbon containing such a ganache will be less than 14 days.

An effective way to reduce the AW value – and thus extend shelf life – is to add sugar to the ganache. Sugar binds part of the otherwise unbound water.

Regular sugar (granulated sugar) is one of the least suitable types of sugar to use in a ganache. If you add granulated sugar to a ganache, the sugar will recrystallize after a relatively short time and release water in the ganache. This will cause both a greatly reduced shelf life and a strange texture.

So other sugars than granulated sugar are needed. Preferably not just one type of sugar but rather a combination of multiple sugars, since by combining different sugars, you can satisfy both requirements in relation to sweetness (not too sweet/sweet enough), texture, and shelf life. In addition to the sugar having an AW-reducing effect in a ganache, it also has an emulsifying effect. So, there are several reasons why it is necessary to add sugar to a ganache (if it is to be used as a filling in chocolate bonbons). But it is important that the right sugars are added - and in the right amounts.

Moreover, we are not interested in reducing the AW value to less than 0.75, because that can only be done by adding excessive amounts of sugar and/or severely limiting the cream content. If you do that, it will significantly affect the taste and consistency. Just try to compare the taste and texture of the chocolate bonbons you can buy in the supermarket (which can last up to six months) with the chocolate bonbons you can produce yourself. It makes better sense to aim for an AW value of between 0.75-0.85, which gives the chocolate bonbons a shelf life of 1-2 months.

In my e-book "CHOCOLATE BONBONS - a practical guide" you will find many different recipes for ganache, all of which are balanced in terms of the different components and which contain different types of sugar. These ganaches all have a shelf life of 1-2 months.