.mrmalty-calculator-wrapper {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 0 auto;
padding: 20px;
background-color: #f9f9f9;
border: 1px solid #e0e0e0;
border-radius: 8px;
}
.mrmalty-header {
text-align: center;
margin-bottom: 25px;
}
.mrmalty-header h2 {
color: #333;
margin: 0;
}
.mrmalty-row {
display: flex;
flex-wrap: wrap;
gap: 20px;
margin-bottom: 20px;
}
.mrmalty-col {
flex: 1;
min-width: 250px;
}
.mrmalty-label {
display: block;
font-weight: 600;
margin-bottom: 8px;
color: #555;
}
.mrmalty-input, .mrmalty-select {
width: 100%;
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
}
.mrmalty-btn {
width: 100%;
background-color: #d35400;
color: white;
border: none;
padding: 15px;
font-size: 18px;
font-weight: bold;
border-radius: 4px;
cursor: pointer;
transition: background-color 0.3s;
}
.mrmalty-btn:hover {
background-color: #a04000;
}
.mrmalty-results {
margin-top: 30px;
background-color: #fff;
border: 1px solid #ddd;
border-radius: 6px;
padding: 20px;
display: none;
}
.mrmalty-result-row {
display: flex;
justify-content: space-between;
padding: 12px 0;
border-bottom: 1px solid #eee;
}
.mrmalty-result-row:last-child {
border-bottom: none;
}
.mrmalty-result-label {
color: #666;
font-weight: 500;
}
.mrmalty-result-value {
font-weight: 700;
color: #2c3e50;
}
.highlight-result {
color: #d35400;
font-size: 1.2em;
}
.mrmalty-note {
font-size: 0.85em;
color: #777;
margin-top: 5px;
font-style: italic;
}
/* Content styling */
.article-content {
max-width: 800px;
margin: 40px auto;
line-height: 1.6;
color: #333;
font-family: inherit;
}
.article-content h2 {
color: #2c3e50;
border-bottom: 2px solid #d35400;
padding-bottom: 10px;
margin-top: 30px;
}
.article-content h3 {
color: #d35400;
margin-top: 25px;
}
.article-content ul {
background: #f0f0f0;
padding: 20px 40px;
border-radius: 5px;
}
.article-content li {
margin-bottom: 10px;
}
function calculateYeast() {
// Inputs
var gravity = parseFloat(document.getElementById('wortGravity').value);
var volume = parseFloat(document.getElementById('wortVolume').value);
var type = document.getElementById('yeastType').value;
var mfgDateStr = document.getElementById('mfgDate').value;
var targetRateOverride = parseFloat(document.getElementById('targetRate').value);
// Validation
if (isNaN(gravity) || gravity 1.200) {
alert("Please enter a valid Specific Gravity (e.g., 1.050)");
return;
}
if (isNaN(volume) || volume 0) {
rate = targetRateOverride;
}
// 1. Convert Gravity to Plato
// Formula: Plato = 259 – (259 / SG)
var plato = 259 – (259 / gravity);
// 2. Convert Volume to Milliliters
// 1 Gallon = 3785.41 mL
var volumeMl = volume * 3785.41;
// 3. Calculate Total Cells Needed (in Billions)
// Formula: (Rate * mL * Plato) / 1000 (since rate is usually million/ml/P)
var cellsNeeded = (rate * volumeMl * plato) / 1000;
// 4. Calculate Viability based on Date
var mfgDate = new Date(mfgDateStr);
var today = new Date();
// Difference in time
var diffTime = Math.abs(today – mfgDate);
var diffDays = Math.ceil(diffTime / (1000 * 60 * 60 * 24));
// Linear decay assumption: roughly 0.7% loss per day (approx 21% per month)
// Mr Malty approximation: Viability = 100 – (Days * 0.7)
var viability = 100 – (diffDays * 0.7);
if (viability < 10) viability = 10; // Floor at 10% for calculation safety (though really it's likely dead)
if (diffDays < 0) viability = 100; // Future date handling
// 5. Calculate Packs Needed (Liquid)
// Standard pack = 100 Billion cells at 100% viability
var cellsPerPack = 100 * (viability / 100);
var packsNeeded = cellsNeeded / cellsPerPack;
// 6. Dry Yeast Calculation
// Assumption: Dry yeast has ~20 Billion cells per gram
var dryCellsPerGram = 20;
var dryGramsNeeded = cellsNeeded / dryCellsPerGram;
// Standard dry sachet is 11.5g
var dryPacksNeeded = dryGramsNeeded / 11.5;
// Display Results
document.getElementById('resPlato').innerText = plato.toFixed(1) + " °P";
document.getElementById('resCells').innerText = Math.round(cellsNeeded) + " Billion cells";
document.getElementById('resViability').innerText = Math.round(viability) + "%";
document.getElementById('resPacks').innerText = packsNeeded.toFixed(1) + " vials/packs";
document.getElementById('resDry').innerText = dryGramsNeeded.toFixed(1) + " g (" + dryPacksNeeded.toFixed(1) + " sachets)";
document.getElementById('resultsArea').style.display = 'block';
}
Understanding the Mr. Malty Pitching Rate
In the world of homebrewing, "Mr. Malty" refers to the legendary yeast calculator standards popularized by Jamil Zainasheff. Pitching rate refers to the number of yeast cells added to the wort to begin fermentation. Getting this number right is arguably the most critical step in producing high-quality beer that is free of off-flavors.
Why Pitching Rate Matters
Yeast are living organisms that need to reproduce before they begin the heavy lifting of converting sugar into alcohol. If you under-pitch (add too few cells), the yeast become stressed as they struggle to reproduce enough colonies to ferment the batch. This stress leads to:
- Esters and Phenols: Unwanted fruity or spicy flavors.
- Stuck Fermentation: The yeast give up before consuming all sugars, leaving a sweet, unstable beer.
- Infection Risk: A slow start gives bacteria and wild yeast a chance to take hold before your brewer's yeast dominates.
Conversely, over-pitching can lead to a lack of distinctive yeast character, though it is generally less common and less detrimental than under-pitching.
The Pitching Rate Formula
This calculator uses the standard pitching rate formula widely accepted in the brewing industry:
Total Cells = (Pitch Rate) × (Volume in mL) × (Density in Degrees Plato)
The Pitch Rate is measured in million cells per milliliter per degree Plato. Standard rates are:
- Ale: 0.75 (ranges from 0.5 to 1.0 depending on gravity)
- Lager: 1.50 (Lagers require roughly double the cell count of ales)
- Hybrid: 1.00 (For Kolsch or California Common styles)
Yeast Viability
Liquid yeast degrades over time. A fresh vial or smack-pack typically contains about 100 billion cells. However, viability drops as the yeast consumes its glycogen reserves while sitting in the fridge. This calculator estimates viability based on the manufacturing date using a linear decay model (roughly 20-21% loss per month).
If your yeast is several months old, the calculator will show a low viability percentage, indicating you need significantly more packs or, more ideally, you should prepare a yeast starter to revitalize the culture and grow the cell count before brewing.
Liquid vs. Dry Yeast
Liquid Yeast: Offers more variety in strains but lower cell counts per package. It degrades faster and often requires a starter for beers with a gravity over 1.050.
Dry Yeast: Generally has a much higher cell count (approx. 200 billion+ cells per 11.5g sachet) and is very stable. It typically does not require a starter, just proper rehydration.