Decarboxylation

Cannabis produces cannabinoids in acidic form. THCA carries a carboxyl group; applying heat removes it as carbon dioxide and leaves delta-9-THC. CBDA becomes CBD by the same route, as do the other acidic cannabinoids.

Because a carbon dioxide molecule leaves, the product weighs less than the starting material. The molecular weight ratio is approximately 0.877, which is where the standard total THC formula comes from: total THC equals THC plus 0.877 times THCA. A fully decarboxylated gram of material containing 20 percent THCA does not yield 20 percent THC; it yields closer to 17.5 percent.

That factor is worth internalising, because it explains a lot of disagreement about potency figures. A number that adds the acid and neutral forms without applying it reads roughly twelve percent higher than one that does.

Guide: how potency figures are calculated

The commonly used home range is roughly 110 to 120 degrees Celsius for about 30 to 45 minutes, material spread thin and covered. Published laboratory work on decarboxylation kinetics broadly supports that region as a reasonable compromise for converting most of the THCA without losing much of the product.

The important framing is that this is a curve, not a threshold. The reaction proceeds continuously and its rate rises sharply with temperature. Lower and longer gets you to a similar conversion while driving off fewer terpenes. Higher and shorter gets you there faster and costs aroma and, past a point, product.

Smoking and vaporizing decarboxylate instantly at the point of combustion or vaporization, which is why none of this applies to them. It applies to anything eaten, and to anything infused.

NoteThere is no single correct time and temperature. Anyone quoting one to the minute is describing their oven, not the chemistry.

A domestic oven thermostat does not hold a temperature. It cycles around a setpoint, often by twenty degrees or more, and the reading on the dial is frequently well off the actual air temperature. An oven thermometer placed next to the tray is the cheapest improvement available.

Material depth matters as much as air temperature. A thick pile heats unevenly, so the outside overshoots while the centre is still converting. Spread material in a thin layer and stir once partway through.

Moisture matters too. Water evaporating from wet material absorbs energy and holds the material cooler than the surrounding air, so freshly dried or rehydrated material converts more slowly than dry material at the same oven setting.

Covering the tray, with foil or a lid, reduces terpene loss to the air and is close to free. Sealed jar methods do the same thing more thoroughly, with the trade-off that a sealed vessel under heat builds pressure and needs to be treated with care.

Past the point of full conversion, continued heat starts destroying what you made. THC oxidises to CBN, a process accelerated by heat, air and light. Terpenes are largely gone well before that; the light monoterpenes leave at temperatures below those used for decarboxylation, which is why a decarbed kitchen smells the way it does.

Visually, over-decarbed material darkens and crumbles to dust. That is the usual sign that the temperature was too high or the time too long. It is not recoverable.

The practical consequence is that the failure is asymmetric. Slightly under-decarboxylated material still contains THCA that will partially convert during a subsequent hot infusion. Over-decarboxylated material has already lost product. When in doubt, err low.

Infusing into fat involves holding material at temperature for an extended period, which does perform some decarboxylation on its own. Relying on that alone is unpredictable, because infusion temperatures are usually lower and the presence of fat and water changes the picture.

The reliable sequence is to decarboxylate first, as a dedicated step with the material spread thin, and then infuse. Doing so separates the two variables so that a disappointing result tells you which stage to change.

One genuine advantage of decarboxylating before infusion is that the aroma loss happens in the oven rather than in the oil, which some people prefer for flavour reasons and others do not.

Guide: infusion and dosing

There is no home method that tells you what fraction of the THCA converted. Colour, smell and texture are weak proxies, and the various colour-change test kits sold for potency do not distinguish acid from neutral forms with any useful precision.

What that means practically is that any dosing calculation built on a home decarboxylation carries an unknown error term. You can reduce it by controlling temperature and depth, and you can bound it by testing a finished product at a laboratory, but you cannot eliminate it by being careful. Treat home-made edible potency as an estimate with a wide interval, and dose accordingly.