Free tool
Fortifying is just blending a stronger spirit into your wine, mead or cider to push the strength up, the way port and sherry are made. Tell it what you have, then either what you're adding or what you're aiming for, and it works out the rest.
Add about 1432 ml of spirit at 40% to 4.50 L at 11%, and you land near 18% in roughly 5.93 L.
Blend two liquids and the result sits at the volume weighted average of their strengths. To go the other way and find how much spirit to add for a target, the classic winemaker's sum is:
A stronger spirit gets you to the same target with less liquid, so it dilutes the flavour of your wine less. One thing worth knowing: as a wine climbs past roughly 18 to 20% the alcohol halts most wine yeast. That is how port and sweet sherry hold on to their sweetness, and why fortifying before fermentation has finished leaves a sweeter drink.
Blending two liquids gives a strength that is the volume weighted average of the two. Multiply each volume by its ABV, add them together, and divide by the total volume. This calculator does it both ways: the final strength from a measure you add, or the measure you need to hit a target.
The formula is: spirit to add = base volume × (target − base ABV) ÷ (spirit ABV − target). For 4.5 litres of 11% wine taken to 18% with a 40% spirit, that is about 1.43 litres. Use a stronger neutral spirit at 96% and you only need around 0.4 litres, which dilutes the flavour far less.
A neutral grape spirit or brandy at around 40% is traditional for port and sherry style wines. A stronger neutral spirit reaches the same target with less added volume, so it dilutes the flavour less. Whatever you use, put its real ABV into the calculator.
Once a wine reaches around 18 to 20% the alcohol is strong enough to halt most wine yeast, which is how port and sweet sherry keep their sweetness. Fortify before the sugar has all fermented and you get a sweeter, stronger result.
Demijohn Journal tracks your gravity readings, works out ABV as you go, and keeps your recipes and fermentation history together. Free.
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