Homebrewing Basics: Brewing Steps, Gravity and ABV

How beer is made at home, why sanitation decides most batches, how to read a hydrometer, and how alcohol by volume is calculated from two gravity readings.

Updated October 28, 2026

Calculate Your ABV

Beer is four ingredients: water, malted grain, hops and yeast. The brewer turns the starch in the malt into sugar, boils that sugary liquid (called wort) with hops, cools it, and gives it to yeast. The yeast eats the sugar and makes alcohol and carbon dioxide. Everything else in homebrewing is control: of temperature, of cleanliness, and of measurement.

This page follows the process as the American Homebrewers Association and John Palmer's How to Brew teach it, then explains the two numbers every brewer records: original and final gravity.

The Brewing Steps

The same sequence applies from a one-gallon kit to a brewery

01

Clean and sanitize

Clean every fermenter, hose and lid. Anything that touches the wort after the boil must also be sanitized.

02

Mash or steep

All-grain brewers soak crushed malt in hot water, usually around 148 to 158°F (64 to 70°C), so enzymes convert starch to sugar. Extract brewers dissolve malt extract instead.

03

Boil with hops

The wort boils, commonly for 60 minutes. Hops added early give bitterness; hops added near the end give aroma. The boil also sterilizes the wort.

04

Chill quickly

Cool the wort to pitching temperature fast. Warm, sweet wort is an easy target for bacteria.

05

Take the OG, aerate, pitch

Measure the original gravity, add oxygen by shaking the cooled wort, and pitch the yeast.

06

Ferment

Keep the fermenter inside the temperature range printed by the yeast maker. Fermenting too warm is a common cause of harsh, fruity or solvent-like flavors.

07

Take the FG, package

When the gravity stops changing, record the final gravity. Bottle with a measured dose of priming sugar or transfer to a keg, then let the beer carbonate.

Cleaning vs Sanitizing

Most failed batches trace back to this step

Cleaning removes visible soil: dried wort, yeast rings, hop residue. Use an unscented cleaner made for brewing equipment and a soft cloth, because scratches in plastic hide bacteria that no sanitizer reaches.

Sanitizing reduces the remaining microbes to a level that cannot outcompete your yeast. Sanitizer only works on a clean surface. Homebrewers commonly use acid-based no-rinse sanitizers or iodophor. Mix and use them exactly as the label states, including the contact time.

The hot side (mashing and boiling) needs cleaning only, because the boil kills microbes. The cold side (fermenter, airlock, hydrometer, bottles) needs both. Unwanted sour or medicinal flavors usually point to the cold side.

Reading Gravity

Specific gravity is the density of your wort compared with pure water

Pure water has a specific gravity of 1.000. Dissolved sugar makes wort denser, so a typical wort reads somewhere above 1.040. Brewers often talk in gravity points: 1.050 is 50 points. As yeast converts sugar into alcohol, which is lighter than water, the reading falls.

A hydrometer floats in a sample jar; you read the scale where the liquid surface crosses it. It is calibrated for one temperature, usually 60°F or 68°F, so cool a warm sample or correct the reading. Never pour a sample back into the fermenter.

A refractometer needs only a few drops and works well for the original gravity. After fermentation starts, alcohol bends light differently from sugar, so final-gravity readings from a refractometer need a correction formula before they mean anything.

ABV and Attenuation Calculator

Enter your original and final gravity. Results update as you type.

5.25%
ABV, standard formula
5.34%
ABV, alternate formula
80.0%
Apparent attenuation
40
Gravity points dropped

The formulas

The standard homebrew estimate:

ABV = (OG - FG) x 131.25

The alternate formula, published by Michael L. Hall in "Brew by the Numbers" (Zymurgy, the American Homebrewers Association journal, Summer 1995):

ABV = (76.08 x (OG - FG) / (1.775 - OG)) x (FG / 0.794)

Apparent attenuation, the share of gravity points the yeast consumed (apparent, because alcohol reads lighter than water):

AA = (OG - FG) / (OG - 1) x 100

The two results agree for normal-strength beer and spread apart as gravity rises; for strong beers the alternate formula is generally considered closer. Both are estimates from density, not a laboratory measurement. You can type gravity as 1.050 or as points (50).

Grouped bar chart of ABV from the standard and alternate formulas: OG 1.050 / FG 1.010 gives 5.25% and 5.34%, OG 1.080 / FG 1.016 gives 8.40% and 8.96%, OG 1.100 / FG 1.020 gives 10.50% and 11.58%, OG 1.120 / FG 1.030 gives 11.81% and 13.56%
At normal strength the two formulas differ by about 0.1 point; at OG 1.120 the gap grows to almost 1.8 points.

Frequently Asked Questions

How is the ABV of homebrew measured?

Homebrewers measure the specific gravity of the wort before fermentation (original gravity, OG) and of the beer after fermentation (final gravity, FG). The drop in gravity shows how much sugar the yeast turned into alcohol and carbon dioxide. The common estimate is ABV = (OG - FG) x 131.25.

How do I know fermentation is finished?

Take hydrometer readings a few days apart. When the gravity stays the same over two or three readings, fermentation is complete. Bubbles in the airlock are not a reliable sign. Bottling before the gravity is stable can over-carbonate the bottles.

Is homebrewing beer legal in the United States?

Yes. Federal law has allowed homebrewing since 1979, and Mississippi and Alabama became the last states to legalize it in 2013. Under 27 CFR 25.205, an adult may produce up to 100 gallons a calendar year, or 200 gallons for a household with two or more adults, for personal use and not for sale. Local rules can still apply.

Sources

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