I have a traditional pressure cooker and the temp in a pressure cooker is 250F so I am not sure about using this to decarb but wonder if it would be OK to make butter in?
If it's weighted, get a 5 lb weight for it. It will top out at a lower temp than typical 15 lb cookers (US standard, I think UK standard is 13 PSI or thereabouts). Also keep in mind the ultimate temperature is dependent on your elevation.
I, too, wonder about using pressure cooking to make cannabutter. I live at about 5700' so my Instant pot, that tops out at 11.6 PSI, won't get to 250F like your conventional one would at sea level. It tops out lower than that. 243F at sea level on high, 233F at sea level on low. (High on an IP is 11.6 PSI and low is 7.2 PSI) At 5700' above sea level its even lower than that. Not sure exactly what, can't remember the formula, LOL! But its lower at higher elevations for any pressure cooker.
I will have to try this. BTW, they are now making at least some accessories for the small Instant Pot and you can get both the small and large IPs in the 10-in-1 Ultra versions now, which is the version I suggest. You can do fermentation in it (yogurt, dosa batter), slow cook, pressure cook, and you have much finer temperature control than any other IP model available to date. The Ultra models will hold temps within a 3C/5F range for the "custom temperature" settings. Instead of using the IP in pressure mode, decarbing could be done with a much finer control of temp on the custom temp settings, or possibly one of the preset cycles.
Of course if you go non-pressurized you may not be getting the same odor control, but when I water-wash my ABV there is hardly any smell at all. Fresh weed is a lot smellier though, so if odor is a problem you may want to stick with the pressurized settings.
IP ultra models currently come in the following sizes:
Small = 3 qt
Regular = 6 qt
Large = 8 qt
Last I checked IP Temps in the Ultra were as follows:
Low Yogurt: 86F to 93F
Reg Yogurt: 97F to 109F
Sterilize: 160F to 180F
Keep Warm function: 63 - 78°C (145 ~ 172°F);
Slow Cook function:
Low: 82-87.8°C / 180-190°F;
Med: 87.8-93°C / 190-200°F;
High: 93-99°C /200-210°F
Sauté function:
Low: 135 -150°C (275 -302°F);
Med: 160 -176°C (320 -349°F);
High: 175 - 210°C (347-410°F)
And custom temps in the range of 104F to 208F, the IP will actually operate in a 3C/5F range around the selected temp. The custom temp is NON pressurized cooking.
The above table assumes you are at sea level. Looks like the MEDIUM or HIGH slow cooker settings might be ideal for decarb. Problem is I can't seem to find a consensus on the "best" decarbing temps nor descriptions of how much is lost if you decarb at less-than-ideal temps. Some sites claim 250F IS the proper decarbing temp.
This site recommends an hour at 240F:
http://marijuanagrowershq.com/decarboxylating-cannabis-turning-thca-into-thc/
It seems to have worked for some people to go ahead and do it under pressure and thus at higher temps. I can't say since vaping my fresh material and then using the ABV means my material is effectively pre-de-carbed and I only need to make the butter.
Apparently oven decarb results in the loss of desirable THC up to 1/3rd, due to the high temperature variation. Doing this step in an Instant Pot involves way less temperature variation, depending on the cycle selected. The least variable temp seems to be to select a custom temp under the non-pressurized settings. But that does top out at 208F so if the desirable temp is higher than that, probably need to stick with one of the other cycles.