"It looked right when I pulled it"
This is the commonest sentence in nut roasting and it is almost always describing the same failure. The roast did look right at the pull. It then carried on for several minutes in a bowl on the counter, and the batch you tasted an hour later was not the batch you pulled.
Nothing about leaving the heat stops the chemistry. Browning reactions run at temperature, and the nuts are still at temperature. The only thing that ends a roast is getting the temperature down, and that is a job you have to actually do.
The physics, which are worse for nuts than for anything else
Nuts are roughly a quarter to three-quarters fat. Fat stores a lot of heat, and a hot, oily nut is a small, well-insulated battery of it. Six pounds of nuts at roast temperature is a genuinely large amount of stored energy sitting in a material that gives it up slowly.
Compare it with coffee, which is drier and less oily, and where carry-over is a real effect but a manageable one. With nuts it is often the dominant variable in how the batch tastes — larger in its effect than a thirty-degree difference in where you set the grill.
A pile insulates itself
Tip a batch into a bowl and you have built the worst possible cooling geometry. The nuts on the outside of the pile lose heat to the air. The nuts in the middle lose heat to more hot nuts, which is to say they barely lose any at all. The centre of a deep pile can sit near roast temperature for minutes.
That does two kinds of damage. The obvious one is that the batch goes darker than you intended. The less obvious one is that it goes unevenly darker — you have created a temperature gradient and cooked a gradient into the flavour, so a batch that was consistent coming out of the drum is not consistent going into the jar. If you have ever found scorched notes in a batch that never looked scorched, this is usually where they came from.
