Lemmitor @A_norny_mousse@feddit.org in this community tipped that if the process serves and luck is on one's side, fermented birch sap can be better than champagne. Right now is the time when sap can be collected, so I'm giving it a shot!
The tree isn't terribly bothered, the tap hole is only a few millimeters deep. I only do one tap per tree.
Plan is to empty these tap bottles off several trees once a day into an intermediate container, use a Campden tablet per container and keep the intermediates in the fridge until I have enough, five liters maybe? Then one liter yeast starter, possibly with some cane sugar to lend a little extra aroma and colour (the sap is clear). Ferment fingers crossed. Serve force carbonated. Wish mi luck :D
Yeah - moderate temperature, huge surface area and plenty of air movement across the surface would bring best results. I'm absolutely doing this again next spring, aiming for 20 liters of sap so I can put my fancy fermentation setup to work. Was thinking of using two of those under-the-bed storage boxes to make an evaporating setup, having the lids on and feeding in air with an aquarium pump that has two outputs. I'd still add dark syrup for colour though.