6 kg or 12 kg — size from sales, not from budget

Two ways people get sizing wrong: they buy to their budget, or they buy to their ambition. Both end with a machine that does not fit the work.

The right order is the reverse: work out how many kilos of roasted coffee you can sell in a day, then size backwards.

Three steps

Sales per day → green beans per day. Assume 15% weight loss. To ship 30 kg of roasted coffee you need 30 ÷ 0.85 ≈ 35 kg of green.

Green per day → batches. Divide by the mid-point batch. The 6 kg model takes 1–7 kg per batch; call it 4.5 kg. That is 35 ÷ 4.5 ≈ 7.8 batches.

Batches → can one person keep up? This is the step everyone skips. One operator can realistically manage four to six batches a day, including loading, discharging, cooling, cleaning and packing.

So 30 kg a day is not a 6 kg machine. It is a 12 kg or 15 kg.

Sizing table

Based on four batches a day, mid-point batch weight, 15% loss — what one operator can hold:

With a second pair of hands and six batches a day, shift the whole table up one row.

What oversizing actually costs

The drum runs half-full and the curve drifts. Drums are designed around a filled load. Put 2 kg into a 6 kg drum and the bean mass is thin, heat transfer is faster, the turning point is hard to catch, and first crack arrives early and inconsistently. Same bean, two different results.

You lose the small-batch advantage you paid for. People buy big for "later". If daily work is small batches, a smaller machine running full beats a big one running empty.

Gas is billed per machine, not per kilo. A large drum loses more heat to the room.

When to go up a size

1. You already have committed volume — a contract, not a hope
2. You roast for other people and need headroom
3. The site and power are sized once and adding machines later is expensive

Otherwise buy one size down. Two smaller machines cost less than one large one, and when one is down you can still ship.