Pour a gallon of milk into a large stock pot. Set the burner to medium-high heat and bring the milk to a temperature of 180 degrees F. Hold the milk at that temperature for 5-10 minutes, whisking often.
One Gallon of Whole Milk
Once the milk has maintained a temperature of 180 for 5-10 minutes, remove the pot from heat and let the milk temperature come back down to 115-120 degrees. Add in the vanilla and maple and stir well to combine. While the milk is cooling, begin adding hot tap water to your cooler. The temperature should be between 110-120 degrees Fahrenheit. The temperature should not exceed 120 degrees or you risk harming your culture.
1/4 Cup Pure Maple Syrup, 4 Tbsp Pure Vanilla Extract
Pour most of the sweetened milk into a large gallon mason jar, or into multiple smaller jars, leaving 1-2 cups of milk in the stock pot. Whisk your starter culture (store-bought) yogurt into the remaining milk and whisk well to thoroughly combine.
1/4 Cup Store bought organic yogurt
Add the milk + starter culture mixture back in to the heated milk and whisk really well to make sure it is evenly distributed throughout. Then, secure your lid so that it is airtight.
Carefully place your mason jar into the cooler filled with warm water. Make sure that the water comes at least half way up the jar. Check the temperature to make sure it is still between 110-115 Fahrenheit and close the lid.
Let the yogurt culture in the cooler overnight or for 8-10 hours. Be careful not to jostle the cooler.
Carefully remove the yogurt from the cooler and transfer it to the fridge to cool and continue to "set" for 4-6 hours before eating.
Top with your favorite fruit, jam, granola, honey, or cereal and enjoy!