# The Pearson Square: Ancient Math, Perfect Wine
The Pearson Square is one of the oldest and most elegant tools in winemaking mathematics. Developed in the 19th century, it allows any winemaker — professional or amateur — to calculate blending ratios with nothing more than subtraction. Our tool digitises this visual method and adds real-time feedback, so you spend less time calculating and more time crafting.
15–18% ABV Vermouth
18–20% ABV Port
15–17% ABV Sherry
Why fortify at 18%?
Above roughly 15% ABV, Saccharomyces cerevisiae — the primary wine yeast — becomes inhibited. By 18%, fermentation is completely arrested. This is why Port retains residual sweetness: spirits are added mid-fermentation, killing the yeast before all sugar is consumed.
Pro Tip: Measure at 20°C
Alcohol density changes with temperature. Official ABV measurements are calibrated at 20°C. If your spirit or wine is significantly colder or warmer, apply a correction: roughly +0.04% ABV per °C below 20°C.# The Craft Vermouth Renaissance
Southern Europe is experiencing a craft vermouth renaissance. Barcelona, Valencia, and San Sebastián have reclaimed la hora del vermut as a cultural institution, and small producers across Spain, Italy, and France are bottling remarkable expressions. This has created a new generation of home producers who want the technical tools to match their ambition.
Who is this tool for?
Home winemakers: Fortify your harvest with precision instead of guesswork.
Craft vermouth producers: Prototype new ABV targets before scaling to full batches.
Spirits educators: Demonstrate the Pearson Square method visually in workshops.