Calculating roasted weight

What’s the best way to gauge weight loss of your beans? If I’m going for a 12 oz (340 g) roasted weight, should I be looking to aim for a bit over a pound? I’d like to try some distribution to some friends/neighbors and thinking about 12 oz bags. I’m sure it’s easier if I’m banging out a few pounds at a time but I don’t think I’ll be doing more than about 2 lbs at a time or so.

If I understand correctly, you want to calculate the weight of greens to use as the charge weight in order to yield about 340 gm of roasted coffee.

A sample roast should give you the expected weight loss in % for the beans. That weight loss % should be very consistent regardless the batch size. The calculation is pretty straightforward-

  • Subtract the expected weight loss % from one, then
  • divide your desired yield (final weight) by that value to get the batch size of the greens.

For instance-

  • Sample weight loss = 15%; use 0.15
  • Subtract weight loss from one = 1 - 0.15 = 0.85
  • Desired yield is 340 gm
  • Charge weight (batch size) = desired yield divided by 0.85 = 340 / 0.85 = 400 gm

So if you charge with a 400 gm batch of greens with an expected weight loss of 15% you should hit about 340 gm yield.

Weight loss % will probably be closer to 17% +/- though I just did some Timor decaf that had a weight loss % of 13.5%. Your sample roasts & roast history will be your guide.

If I misinterpreted your question let me know.

Bruce

Thanks. What I’m hoping for is a sense of what a general rule might be. I’m not wanting to do a sample roast first just to calculate it so I’m wondering if say, 30% weight loss might be reasonable? What do you typically see in terms of pre and post roast differential?

Weight loss is also affected by how dark you roast. It may be best to take a look at your roast data as well since it is a reflection of your roasting style and you may see a pattern. For me roasting in batches of ~500g to just before SC I get ~16-17% loss.

If you enter data in the weight fields in RT3 for each roast you will have the info needed for each bean in your inventory to estimate starting weight for a planned final weight. That’s all that’s required to estimate final weight based upon a known starting weight.

As @blacklabs mentions, weight loss-% is pretty consistent and definitely dependent upon how dark you roast. The only generalization is that weight loss will be somewhere in the vicinity of 17% range (though as I mentioned above I saw 13% weight loss on some Timor decaf beans). 30% weight loss is definitely not reasonable.

Bruce

Moisture content of the green beans will also have an impact on the roasted weight. 12% being the ideal scenario, it can be a bit up or down based on storage conditions. Some overage will leave a bit extra but no shortfall. I guess 30% leaves enough leeway for even dark roasts with higher moisture content greens.