How do you calculate the alcohol percentage in home brew beer when not have an initial specific gravity reading?

To calculate the alcohol percentage (ABV) in home brew beer without an initial specific gravity reading, you can use the following formula:

ABV = [(Final Specific Gravity - Original Specific Gravity) / 1.05 - 1] x 100

Here's a step-by-step explanation of how to calculate the ABV:

1. Obtain the Final Specific Gravity (FG):

- Use a hydrometer or refractometer to measure the specific gravity of your finished beer.

- Note down the final specific gravity reading.

2. Estimate the Original Specific Gravity (OG):

- Since you don't have an initial specific gravity reading, you can use an estimated OG based on your recipe.

- Calculate the OG by adding the total gravity points from your recipe to 1.000.

- For example, if your recipe has an estimated starting gravity of 1.050, use 1.050 as your OG.

3. Substitute the Specific Gravity Values:

- In the formula above, replace the "Final Specific Gravity" with the actual FG you measured.

- Replace the "Original Specific Gravity" with the estimated OG based on your recipe.

4. Calculate the ABV:

- Perform the calculations inside the brackets and subtract the result from 1.

- Multiply the final value by 100 to convert it to a percentage.

5. Interpret the Result:

- The final calculation will give you the estimated ABV of your home brew beer.

Remember that since you're using an estimated OG, the calculated ABV may not be as accurate as it would be with an actual initial specific gravity reading. It's always better to take an OG reading at the beginning of fermentation to get a more precise ABV calculation.