# 🍺 Top-down Brew: Documentation and Explanation

## Overview

This documents the finer points of the beer engine including documentation for how the calulcations are performed. Knowing these inner operations may be useful for advanced homebrewers.

## Original gravity (og:)

This value sets the gravity targeted for the batch. It's a crucial starting point. Applying percentages to this value determines the weights that will be needed.

Gravity can be used as either specific gravity (example: 1.048; commonly used by homebrewers) or degrees Plato (example: 12; commonly used by professional brewers). Values smaller than 1.2 are assumed to be in specific gravity units, with larger values being assumed to represent degrees Plato.

## Target volume (vol:)

This is the volume desired at the end of the boil. The volume units can be liters, gallons, or US barrels. The preferred units of measurement are set by the system variable. This calculator does not estimate boil-offs or the starting boil volume needed for the target volume. If the target volume is unclear or missing, the default value is 5, an assumption for 5 US gallons.

## System (system:)

This sets the measurement system being used. Most homebrewers will want to set this to either "metric" or "US". The "barrels" setting is US, but with volume adjusted to represent barrels. When the desired measurement units are missing or unclear, the system defaults to US.

## Mash efficiency (eff:)

Mash efficiency is the anticipated percentage of sugars that will extracted from the grain bed during sparging. If this is unknown for your system, try the following values based on the sparge method: Steeping (50%), No-sparge or brew-in-a-bag (65 to 75%), Batch sparge (80%), or Continuous (fly) sparge (85 to 90%). If mash efficiency is missing or unclear, the default value is 75%.

## Malts and grains (malt:)

These lines are for the mashed grains used in all-grain or partial mash brewing. Each grain needs a separate line. The order of data for each line is malt or grain name, percentage of wort, Lovibond, and yield. The values in a line must be distinguished by commas (comma separated values).

Theoretical yield can be entered as either coarse-grind as-is percentages (example: 80% for two-row malt) or specific gravities (example: 1.037 for two-row malt). The calculations assume that yield values between 1.0 and 1.5 represent specific gravity units. Anything larger than 1.5 is assumed to be a percentage yield. The yield values can come from the analytical sheets provided by major malt companies or by average values suggested in online databases. The theoretical yield of malts is adjusted downward base on the anticipated mash efficiency.

## Sugars and malt extracts (sugar:)

These lines represent fermentables such as sugars or malt extract. The data order in each line is name, percentage of wort, Lovibond, and yield. For malt extracts, the dry and liquid forms typically have a 1.044 (96%) or 1.035 (76%) yield, respectively.

The importance of distinguished malts from sugars is due to mash efficiency. Sugars are not adjusted downward for mash efficiency because sugars are directly added to the kettle. Mash efficiency is not relevant.

## Bitterness (ibu:)

The international bittering units (IBUs) provide an overall target for the desired bitterness. The percentages of each hop addition are treated separately. Assigning a percentage to each hop addition allows the calculator to scale the weights up or down as needed for the desired volume. This approach was inspired, to some degree, by Daniel's approach of calculating backwards from late hop additions in Designing Great Beers.

The BJCP style guidelines provide a range of values typical for each beer style. For clone recipes, commercial brewers often provide IBU values on their web site or the botle label. The bitterness unit to grist unit (BU/GU) ratio is also included in the the output.

## Hops (hop:)

These lines contain the hop data with a separate line for each hop addition. The data order in each line is hop name, IBU percentage, alpha-acid percentage, and boil time in minutes.

IBU percentage is the contribution of a single hop addition to total IBUs. For example, using a single bittering hop addition would be 100% of the IBUs. Late hop additions are typically 10 to 20% of total IBUs due to lower utilization.

The IBU calculations are based upon Tinseth formula. The calculations estimate boiling gravity based a 15% per hour boil-off rate. A deviation from the Tinseth formula is for late aroma additions. Hops with 1 or less minutes in the boil end, such as hop stands, are adjusted upward to have a 5% utilization rather than 0% as calculated by the Tinseth formula.

## Late boil additions (lb:)

Late boil additions are used for non-hop kettle ingredients like spices, yeast nutrients, or Irish moss. The name and dosage must be separated by a comma. The dosage format input must use grams per liter.

## Dry hops (dry:)

These lines are for dry hop additions to the fermenter. Each hop addition has a separate line. The format is the hop name followed by dosage in grams/liter. The following guidelines are suggested doses for pale ales and IPAs.

- 0.5 to 0.9 g/l: Light
- 1.0 to 2.0 g/l: Moderate
- 2.0 g/l: High

US units (ounces and pounds) are not available for this feature.

## Yeast (yeast:)

This calculates the yeast pitching rate for either ales or lagers. The ale pitching rate for wort below 17 degrees Plato (1.068 SG) is .5 g/l for dry yeast or .75 million/mL/°P for liquid yeast. Ales at 17 degrees Plato or higher are 1 g/l (dry) or 1.0 million/mL/°P (liquid). The lager pitching rates are double the ale values.

Yeast calculations are only conducted in metric units.

## Partial mash brewing (lme: or dme:)

Malt extract is often purchased in fixed weights. Examples would be one pound of dry malt extract (DME) or 3.3 pounds of liquid malt extract (LME). This fixed value makes it convenient to enter this fermentable as a fixed weight. The weight is subtracted from the total fermentable sugars needed. While this breaks the philosophy of top-down brewing (percentages to weights), it is convenient for partial mash brewing. Choosing this option means that percentages of wort for the remaining ingredients apply to only the remaining non-extract fermentables.

## Priming (prime:)

This function calculates the amount of priming sugar needed depending on volume, desired carbonation level, and fermentation temperature. Be aware that this requires predicting the fermentation temperature before fermentation has begun. If this changes, the stand-alone priming calculation pages can be used to redo this calculation.