Roast and grind, and what each one decides

The roast does three jobs at once

It develops flavor, it drives off moisture, and it is the kill step. Those pull in the same direction up to a point and then diverge: the roast that tastes best is not automatically the roast that is sufficient, and the second question has to be answered independently of the first.

Darker is a different product, not a better one

A darker roast gives a more pronounced, more bitter result and a visibly darker butter. Buyers have strong preferences and they notice drift of half a shade between jars, which makes roast consistency a commercial problem as well as a safety one.

The grind generates heat

Friction warms the batch, sometimes considerably on a long run, and a warm batch behaves differently: it is thinner, it fills differently and it cools in the jar. That is a reason to watch temperature during grinding even though nothing about it is a safety step.

Fineness and separation

A finer grind gives a smoother product that separates more slowly, because smaller particles settle more slowly. That is a real lever and it is a small one; it will not substitute for a stabilizer if what you want is a product that does not separate at all.

Chunky is a second grind, not a coarser one

The usual approach is a smooth base with chopped nuts folded in, which gives control over both the texture of the base and the size of the pieces. The regulation anticipates this, allowing cut or chopped peanuts to be added to the ground base.

Let it cool before judging it

Both operations are judged wrong when the product is warm: a warm batch is thinner and tastes different, and a hot roast keeps developing on the tray after it leaves the heat. Pull the roast slightly before it looks right, and taste the butter at room temperature rather than at the grinder.

References