In a mortar and pestle, add all of the spices (ginger, nutmeg, cinnamon, cardamom, peppercorns, cloves, and star anise) and lightly crush them to release the flavourful oils. If you do not have a mortar and pestle, you can gently crush the spices on a cutting board with the pack of a wooden spoon.
In a saucepan on medium-heat, add the crushed spices and lightly toast them for 1 minute.
Add water to the saucepan with the spices and bring to a boil. Reduce heat and simmer for 15-20 minutes.
Bring the water and spices back to a boil, then remove from heat. Add the black tea, loose leaf or tea bags, and steep for 5 minutes.
Stir sugar (if using) until dissolved.
Pour the chai concentrate into a glass bottle or jar through a strainer to remove the tea and spices. Let cool to room temperature before sealing and refrigerating. Store in the fridge for up to 1 week.
To use the chai concentrate, begin by mixing equal parts with milk. Add more chai concentrate if you would like it stronger. Pour it directly over iced for an iced chai latte, or heat it first for a hot chai latte.