Brewing beer, wine, or mead involves a fascinating transformation of sugars into alcohol and carbon dioxide through fermentation. The key to monitoring and understanding this process lies in measuring its gravity. Gravity, in this context, refers to the density of the wort (unfermented beer) or must (unfermented wine/mead) relative to water.
Gravity is typically measured using a hydrometer, a specialized tool that floats in the liquid and indicates the density on a calibrated scale. The measurements are usually expressed in "Specific Gravity" (SG) units.
Original Gravity (OG)
Original Gravity (OG) is the measurement of the wort's specific gravity before fermentation begins. It represents the total amount of dissolved solids (primarily sugars) in the wort. A higher OG indicates a higher potential alcohol content and a fuller-bodied beer. For example, an OG of 1.050 means the wort is 50 parts denser than water (where water has an SG of 1.000).
Final Gravity (FG)
Final Gravity (FG) is the measurement of the liquid's specific gravity after fermentation is complete. At this stage, most of the fermentable sugars have been consumed by the yeast, and the dissolved solids are primarily unfermentable carbohydrates and other residual compounds. A lower FG indicates that fermentation has progressed well and most sugars have been converted. A typical FG for many beers might be around 1.010.
Calculating Alcohol By Volume (ABV)
The difference between the Original Gravity and the Final Gravity is a direct indicator of how much sugar has been converted into alcohol and carbon dioxide. The Alcohol By Volume (ABV) is the percentage of alcohol in the final beverage. While various formulas exist, a common and reasonably accurate approximation used by brewers is:
ABV ≈ (OG – FG) × 131.25
This formula estimates the alcohol content based on the specific gravity readings. The factor 131.25 is derived from the density difference between alcohol and the residual sugars.
Why Use This Calculator?
Estimate Alcohol Content: Quickly determine the potential or actual alcohol percentage of your brew.
Track Fermentation: Monitor the progress of your fermentation by comparing OG and FG.
Recipe Formulation: Help in designing recipes with desired alcohol levels.
Quality Control: Ensure your brews meet expected alcohol specifications.
This batch would be estimated to have an alcohol content of approximately 5.25% by volume. The batch volume is provided for context about the overall size of the brew but is not directly used in the standard ABV calculation formula itself.
function calculateABV() {
var initialGravityInput = document.getElementById("initialGravity");
var finalGravityInput = document.getElementById("finalGravity");
var batchVolumeInput = document.getElementById("batchVolume");
var resultDiv = document.getElementById("result");
var og = parseFloat(initialGravityInput.value);
var fg = parseFloat(finalGravityInput.value);
var volume = parseFloat(batchVolumeInput.value);
// Input validation
if (isNaN(og) || isNaN(fg) || isNaN(volume)) {
resultDiv.innerHTML = "Please enter valid numbers for all fields.";
return;
}
if (og = og) {
resultDiv.innerHTML = "Final Gravity (FG) must be less than Initial Gravity (OG).";
return;
}
if (volume <= 0) {
resultDiv.innerHTML = "Batch Volume must be a positive number.";
return;
}
// Calculate ABV
var abv = (og – fg) * 131.25;
// Format result
var formattedABV = abv.toFixed(2);
resultDiv.innerHTML = "Estimated ABV: " + formattedABV + "% (Based on " + volume + " Gallons)";
}