Twelve cups means almost nothing on its own. It could be 1.8 litres or 2.9 litres depending on who is counting, and the difference is 70 grams of coffee. Here is the number for both cases.
First, what a cup is
| Definition | Per cup | 12 cups total | Coffee at 1:16 |
|---|---|---|---|
| Machine mark (US drip) | 5 oz / 148 ml | 1.8 L | 112 g |
| Standard mug | 8 oz / 240 ml | 2.9 L | 180 g |
| Large mug | 12 oz / 355 ml | 4.3 L | 266 g |
| Espresso "cup" | 1 oz / 30 ml | 355 ml | Not applicable |
The first row is the one that trips people up. A machine sold as a twelve-cup brewer almost always holds 1.8 litres, not 2.9, because the industry still counts a cup as five ounces.
Does a big batch taste weaker?
Slightly, and for good reasons. A large mass of water holds temperature better, and a full filter bed extracts more evenly than a thin one. Most people find 1:17 in a large batch tastes like 1:16 in a small one.
The other side is time on the hot plate. After about twenty minutes a heated glass pot begins to cook the coffee, which is the real reason large batches taste stale.
Grind for batch brewing
Medium, slightly coarser than a V60. Batch brewers use longer contact times at 4 to 6 minutes, so a V60 grind will over-extract and taste harsh. If your pot tastes bitter and drying, coarsen before changing anything else.
Brew for a crowd, without a bad last cup
- Brew 8 to 10 cups instead of filling the machine.
- Use a thermal carafe rather than a hot plate if you have a choice.
- Brew a second batch rather than letting the first sit for an hour.
- Preheat the carafe with hot water before brewing.
The arithmetic worth memorising
At 1:16, coffee in grams equals water in millilitres divided by 16. For any batch size, that one line gives you the dose. For 1.8 litres it is 112 g, for 2.9 litres it is 180 g, for 4.3 litres it is 266 g.