Preserving: Making Yogurt in a Thermos

I enjoy yogurt for breakfast and on fresh fruit, so I went to my cookbook library to learn how to make it. While most people are going digital, living off the grid makes print books a valuable resource.

Thank goodness people send their old cookbooks to thrift stores for me to find. Two resources gave me what I needed: Stocking Up by Organic Farming and Gardening and my trusty Fannie Farmer Cookbook.


Using a wide mouth thermos is a simple way to incubate yogurt. I found one at my favourite thrift store for $1.75.

Ingredients from Stocking Up:

1 quart milk (regular or skim)
¼ cup commercial plain yogurt with active cultures

That’s it. Pretty simple. Since I could only incubate three cups, I reduced the recipe proportionally.

Tips say: Use milk and starter no older than five days. Use your last batch as the new starter, but it can weaken over time. After 4 batches, start over with a commercial yogurt.

Whisk milk while heating to almost boiling. Cool to lukewarm (105-115°F).

Tips say: If milk is too hot, it will kill the yogurt bacteria.

Add yogurt starter and gently stir until well mixed.

Tips say: Using too much starter can make your yogurt watery.

Use lukewarm water to warm the thermos then drain.

Pour the yogurt mixture into the thermos and secure the lid. Place in a warm (110°F) location to incubate for 4-6 hours. I covered my thermos with a thermal sock and placed it near the woodstove to stay warm.

Tips say: Don't move or bump or the yogurt may separate into curds. If it incubates too long it can become watery. The longer you incubate the yogurt the sourer it will get.

Open the thermos. The yogurt should be custard like. Transfer to a sealed container and refrigerate for three hours before eating.

Tips say: Yogurt will get firmer during cooling. Homemade yogurt tastes sweeter than commercial yogurt.

My first batch came out so well I made a second. I accidentally knocked thermos on the floor. The yogurt did separate. It tasted fine, I just had to stir the liquid whey back in before eating.

Do you make yogurt? What tips can you share? -- Margy