Prepare the orange. Remove the orange zest in wide strips, trying to leave the bitter white pith behind. Cut the orange in half and squeeze out the juice.
Fill the slow cooker. Add the red wine, orange gin, maple syrup, orange juice, orange zest, orange slices, cinnamon sticks, whole cloves and star anise.
Slow cook. Put the lid on and cook on HIGH for 2 hours or LOW for 3-4 hours, until the wine is hot and fragrant. Slow cookers can vary, so it may need a little longer in some models. You want the wine gently heated rather than boiling.
Strain and serve. Remove the whole spices and orange zest with a slotted spoon or pass the mulled wine through a sieve. Taste and adjust the sweetness if needed.
Notes
Use whole spices rather than ground spices to prevent a gritty texture.
Avoid including the white pith from the orange zest, as it can make the wine bitter.
Add fresh orange slices when serving rather than slow cooking them.
Slow cookers vary, so yours may take a little longer than 2 hours to become fully hot.
Remove the spices before keeping the mulled wine on WARM for an extended period.
For 8 generous servings, double the recipe, using 2 x 750ml bottles of wine, provided your slow cooker has sufficient capacity.
Store cooled leftovers in an airtight container in the fridge for up to 3 days, with all spices and orange zest removed.
Reheat gently in the slow cooker or in a saucepan and avoid boiling.