Work out the syrup ratio for your batch, the ginger bug starter feed, and how much conditioning sugar to add per bottle for carbonation — in ml, litres, US cups or US gallons.
A live culture of grated ginger, sugar and water, fed daily — similar in spirit to a sourdough starter — used to naturally ferment and carbonate the syrup.
The syrup ratio splits your batch volume into equal parts, the same way the Lemonade calculator does, assigning parts to ginger, sugar and water. A 1:1:6 ratio over 8 total parts means each part is one-eighth of the batch — for 1 litre, that's 125ml of ginger and sugar each (converted to weight) and 750ml of water.
The ginger bug is calculated separately because it's not part of the drink itself — it's a live starter culture, fed on its own schedule with fresh ginger, sugar and water in roughly equal weight, similar to how a sourdough starter is maintained. A healthy bug is what ferments the syrup into ginger beer and produces the carbon dioxide that carbonates it.
Bottle conditioning sugar is calculated per litre of the finished liquid being bottled, independent of the syrup ratio — it's simply the food the remaining live culture needs, sealed in the bottle, to produce enough carbon dioxide for a fizzy drink without over-pressurizing it.
The syrup ratio is the ginger, sugar and water mix that becomes the flavour base of the drink. The ginger bug is a separate, ongoing wild-fermentation starter — grated ginger, sugar and water fed daily, similar in spirit to a sourdough starter — used to naturally carbonate and ferment that syrup into ginger beer rather than leaving it as a still cordial.
Roughly 5–9 grams of sugar per litre of liquid being bottled is the standard range for naturally carbonated drinks — lower for a gentle fizz, higher for a stronger one. This is the sugar the remaining live culture ferments inside the sealed bottle to produce carbon dioxide, which is what carbonates the drink.
Too little sugar gives a flat drink; too much can build enough pressure in a sealed bottle to make it dangerous to open, or even cause it to burst. Weighing the priming sugar rather than guessing with a spoon, and using bottles actually rated for carbonation, are both standard safety practice for any naturally conditioned drink.
A roughly 1:1:1 feed by weight gives the wild yeast and bacteria on the ginger's skin enough fresh sugar to keep multiplying, similar to how a sourdough starter needs a regular feed of flour and water. Grating fresh ginger (skin included) for every feed introduces new microbes and keeps the culture active.
