# 🍺 Top-down Brew: Rationale for the Beer Engine calculator

Most homebrew recipes simply provide ingredient weights. This is helpful for beginners because it makes brewing beer a hard-wired process similar to baking cookies from a recipe. Most homebrewing software is similarly focused on weights. Users enter weights, then calculations estimate the likely results.

The emphasis on weights poses limitations on more advanced brewers. Brewing outcomes depend partly upon mash efficiency and hop utilization, which varies depending upon equipment, processes, and ingredients. Weight-focused recipes sometimes need recalibration for these adjustments. This can mean fiddling around with weights in homebrewing software to hit the desired outcome targets, such as style-specific original gravity or IBUs.

It seemed to me that there must be a better approach for advanced brewers. BYO magazine's Ashton Lewis has expressed a similar frustration: "I have witnessed many many positive changes over the last 37 years of homebrewing, yet recipes and recipe talk is a department where things have stagnated." (2023, July-August, p. 22).

The present recipe calculators focus upon batch targets and percentages rather than ingredient weights. Percentages come first, then weights are caculated from the percentages. The ingredient weights are the end point of the calculation process, not the beginning point.

The percentage-to-weight approach provides flexibility. Recipes can be easily adjust to compensate for mash efficiency. The batch size can be simply increased or decreased anywhere from 1 gallon to brewery-level volumes. The preferred measurement system can be switched between metric or US units. Finally, target gravity can be expressed as either specific gravity and degrees Plato.

The key variables are entered in a compact, comma-separated format.

    name: My Favorite Beer
    og: 1.053
    malt: two-row, 100, 3, 80
    hop: Cascade, 100, 5.5, 60
    eff: 75
    vol: 5
    system: US
    yeast: ale
    prime: 2.5, 72

This bare bones description is sufficient to calculate a recipe. Recipes communicated in this format could be much more efficient than the current weight-focused recipes. In addition, users can make small edits to values like malt yield or hop alpha acids to easily customize the recipe to their unique brewing needs.

Another kind of flexibility is freedom: no cost and open licensing. These files can be copied, edited, and used for your own purpose with a Creative Commons license. Attribution is requested.