65 percent soluble solids

What soluble solids means here

It is the dissolved content of the finished product, overwhelmingly sugar, measured as a percentage of the whole. The regulation does not leave the method open: it names the analytical method to be used, which is what a bench refractometer approximates when you read Brix off a drop.

Why 65 and not 60

The figure is not arbitrary and it is not only about sweetness. Below it the gel does not reliably form and the product is no longer hostile enough to spoilage to be shelf stable, so the number sits at the point where both of those hold.

Below roughly that concentration there is too much free water for the pectin network to hold and for the jar to keep without refrigeration. The number is doing two jobs at once, texture and shelf stability, which is why lowering it is not a small change and why a reduced-sugar product is a different standard rather than the same one made lighter.

Reading it rather than guessing it

Three published tests get you to the same point from different directions, and they are on testing the set. The temperature test is the cheapest and the refractometer is the only one that reads the number the regulation is written in.

The reduced-sugar case

A product below the figure is not a bad product and it is not a jam under the standard. It is also a different keeping proposition, which is the part most often missed when a line is planned around less sugar.

An artificially sweetened preserve or jam has its own section of the regulation. It is a separate standard with its own requirements, so a low-sugar product is not an exception to the 65 percent figure; it is outside the standard that contains it.

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