Fermented fruit syrups

The Little Red Door is one of our favourite bars in Paris and the first bar we have come across to ferment fruit syrups to produce a low alcohol fruit beer/wine for use as a cocktail ingredient.

Their most recent menu, launched at the end of October 2014, includes a cocktail made using blanco tequila, grapefruit bitters, biere de table and fermented passion fruit syrup.

Mark Scott, Little Red Door's bar manager, was inspired by the Parisian craft beer scene and the imminent opening of a brewing school in the city to start exploring how both beer and fermentation could be used in cocktails, resulting in fermented passion fruit syrup.

Mark explains the process as follows:

1. Make a passion fruit syrup combining caster sugar, soft brown sugar, a more neutral mineral water (Volvic is a good bet) and fresh passion fruits. The syrup is quite light and not overly sweet so as to allow the passion fruit flavour to come through. Leaving the fruits until they have wrinkled and ripened fully tends to lead to a more pungent, tropical syrup - almost allowing the fruits to begin fermenting naturally.

2. Once the sugars have dissolved the syrup is allowed to cool and infuse further for one hour. It is then strained through muslin into a large container. This removes any large solids but isn't overly aggressive so as not to remove too much flavour. The size of and space in the container will have an effect on the ferment, allowing for more or less room for expansion when the syrup begins to ferment. I use a 5 litre glass jar to ferment a syrup of 3 litres.

3. Pitch the yeast into the syrup. Before this it is beneficial to add the yeast to some warm water at 35°C (95°F). Adding the yeast to warm water before pitching will multiply the organisms and increase the yeast's productivity. We use an American ale yeast in the syrup which does the job of fermenting and adds a little flavour but is pretty much neutral. Adding something like a Belgian saison yeast would impart more estery, bready even 'off' flavours sometimes found in those types of beers. These yeasts are something I've begun looking at for our Spring/Summer menu.

4. When the syrup has dropped to 30°C (86°F) the prepped yeast is added. The syrup is stirred to ensure the yeast spreads and then put in an exposed, cool cupboard overnight. (Be sure to seal with a pressure-relief valve.) In the morning the jar is moved inside into a warmer cupboard where it is left to do its thing for up to three days. It needs to be tasted and nosed daily to make sure its developing as we want it to, but 3-4 days is the average duration. The yeasts may need a kick now and again so agitating the jar is sometimes necessary. Basically a foam should settle on the top and bubble calmly.

5. When the fermentation is complete to our liking the liquid is strained, again through muslin, and is ready for use.

This fermented passion fruit will last around ten days at the freshness we desire and will be around 2-3% alc./vo.. After a couple of weeks it begins to stew a little and the alcohol will become more prominent. It doesn't taste bad exactly it just isn't what we want for the drink anymore.

The finished syrup is kept in the fridge topped with a rubber wine stopper. This will keep out any unwanted bacteria but also prevent CO2 build up and explosions.

In simple terms we make a table beer using fresh passion fruit and added sugar instead of malt barley. To try to produce a consistent syrup we measure the brix level of the finished syrup before fermenting, always use the same shape containers and try to keep the containers in the same areas whilst fermenting. Also using sterilised equipment is important.

We have started to experiment with different hop varieties infusing them into a simple syrup then fermenting that for a number of days then dry hopping the resulting syrup to highlight the variety of flavours in differing hops. These are looking toward the Spring/Summer menu. The freshness and sometimes bitterness can have similar results to using something like Campari or Braulio.