How to Make Cannabutter in a Slow Cooker Using a Mason Jar
To make cannabutter in a mason jar in a slow cooker, first decarboxylate the cannabis in the oven (about 230 to 240°F for 30 to 40 minutes). Put it in a jar with butter, close the lid finger-tight, and stand the jar on a folded towel in the slow cooker.
Add warm water up to the jar’s shoulder and cook on LOW for 3 to 4 hours. Strain, chill and dose very carefully.
Only make cannabutter where cannabis is legal for adults. Homemade edibles have no reliable label, so their strength is an estimate. Start with a tiny amount, wait, and keep everything away from children and pets.
- The mason jar method makes a small, low-odor batch, such as ½ cup of butter.
- A slow cooker water bath stays below boiling, so it cannot scorch the butter, but it is too cool to decarboxylate well.
- Keep the lid finger-tight, not cranked down, and keep the jar off the bottom of the crock.
- Avoid sudden temperature changes: glass jars can crack from thermal shock.
- Health Canada advises starting with 2.5 mg of THC or less and waiting up to 4 hours.
Why use a mason jar in a slow cooker?
Cooking the butter inside a sealed jar, sitting in hot water, keeps most of the smell in and makes small batches easy. The water bath also keeps the temperature steady and below boiling, so the butter never burns.
The trade-off is heat. A water bath cannot go above the boiling point of water, so it does not convert THCA to THC efficiently. That is why the oven decarb step comes first.
Step 1: Decarboxylate in the oven
Raw cannabis contains mostly THCA, which is not intoxicating. Heat turns it into THC. In a 2016 study in Cannabis and Cannabinoid Research, THCA in cannabis extract dropped to near zero after 30 minutes at 110°C (230°F).
- Heat the oven to 230 to 240°F.
- Break up 7 to 10 grams of cannabis into small pieces on a parchment-lined tray.
- Bake for 30 to 40 minutes until lightly toasted and fragrant. Let it cool.
Step 2: Infuse in a mason jar
You will need
- A clean pint (16 oz) mason jar with a two-piece lid, free of chips or cracks
- ½ cup (1 stick) unsalted butter
- Your decarboxylated cannabis
- A slow cooker large enough for the jar to stand upright with the lid on
- A folded dish towel or small rack
- Cheesecloth or a fine strainer
Steps
- Fill the jar. Add the cannabis and butter. Leave at least an inch of space at the top.
- Close finger-tight. Screw the band on until it just stops, so steam can escape if needed.
- Protect the jar. Put the folded towel or rack in the bottom of the crock and stand the jar on it.
- Add warm water. Pour in warm (not boiling) tap water to the jar’s shoulder. Do not cover the lid.
- Cook on LOW for 3 to 4 hours. Keep the slow cooker lid on. Top up with hot water if the level drops.
- Swirl now and then. Using oven mitts, lift and gently swirl the jar every hour to mix the butter.
- Cool, then strain. Let the jar cool in the water for 15 minutes, then strain the warm butter through cheesecloth into a clean container.
- Chill. Refrigerate until firm. Label it clearly.
Never put a cold jar into hot water, or set a hot jar on a cold, wet counter. Sudden temperature changes can crack glass. Start with warm water and let the jar cool gradually.
What temperature is a slow cooker on LOW?
USDA FSIS says slow cookers cook at about 170 to 280°F. In a water bath, the jar can only get as hot as the water, which stays at or below boiling (212°F at sea level). That is safe for butter but too cool for a full decarb.
Keep the slow cooker lid on. It holds the heat steady and stops the water evaporating too fast.
How strong is homemade cannabutter?
Here is the maximum possible, which real butter will not reach. 7 grams at 15% THC contains 1,050 mg of THCA. Multiplied by 0.877, that is about 920 mg of THC at most. Spread through ½ cup of butter (24 teaspoons), that is up to about 38 mg per teaspoon.
Health Canada advises people new to edibles to start with 2.5 mg of THC or less. It says effects can take 30 minutes to 2 hours to begin and up to 4 hours to peak. A first serving of this butter could be a tiny fraction of a teaspoon.
Storing cannabutter safely
- Keep it in a labeled, closed container in the refrigerator, out of reach of children and pets.
- Freeze small portions for longer storage.
- If someone eats it by accident and feels unwell, call Poison Help at 1-800-222-1222 (US).
Frequently asked questions
How long do you cook cannabutter in a mason jar in a slow cooker?
About 3 to 4 hours on LOW, after decarboxylating the cannabis in the oven first.
Can you decarb in a mason jar in a slow cooker?
Not efficiently. The water bath stays at or below boiling. Research shows THCA converts well at about 230°F, so use the oven for this step.
Do you put the lid on the slow cooker?
Yes. Keep the slow cooker lid on to hold the heat steady. Keep the jar lid finger-tight, not fully tightened.
Can I make a small amount of cannabutter this way?
Yes. The jar method suits small batches, such as ½ cup of butter with a few grams of cannabis.
Should I add water inside the jar?
It is optional. A spoonful of water inside the jar can help stop the butter overheating, and it separates out when chilled. Pour it off before using the butter.
The bottom line
Decarb in the oven, infuse butter in a finger-tight mason jar in a warm slow cooker water bath on LOW for 3 to 4 hours, strain and chill. Then dose with great care, starting with 2.5 mg of THC or less.
- Health Canada, Lower your risks: edible cannabis.
- Wang M. et al., Decarboxylation Study of Acidic Cannabinoids, Cannabis and Cannabinoid Research, 2016.
- USDA Food Safety and Inspection Service, Slow Cookers and Food Safety.
- HRSA, Poison Help.
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