Low temp yogurt

jpancerman

Any ideas on how to do a low temp yogurt using a ziploc bag? Thanks! Love the site so far.

Chris_Young_80640

Jp888:

Just to clarify your question, you are looking to use sous vide and a Ziplock-style bag to incubate the yogurt, yes?

It can be done, but as with any fermented food it is critical that you work with extreme care and cleanliness. You are relying on the healthy and helpful bacteria out compete any pathogenic bacteria that may be present. Also, because you are trying to culture aerobic bacteria, it's imperative that your packaging not be vacuum sealed, so using an open Ziplock-style bag is one way to go. Use heavy duty bags. Another strategy are canning jars set into a partially filled sous vide bath. Personally, I would choose canning jars because (a) it will be easier and (b) its easier to sterilize the jars.

I do not have a recipe per se, but what I would do is something like this:

(1) Fill the jars with milk, leaving at least 1 inch / 2.5 cm at the top of the jars. Or fill your Ziplock bags.

(2) Place the jars into a sous vide bath to 185 ° F / 85 °C. If using bags, hang the open end of the bag over the edge of the bath. If using jars, make  sure they don't float, but that the water level of the batch comes most of the way up the side of the jars. Agitate the bags or stir the milk in the jars with a clean spoon from time to time to ensure even heating. The milk should spend about 30 minutes at 185 °F / 85 °C, which not only pasteurizes it (killing off harmful bacteria) but also denatures casein and whey proteins in the milk to make them easier to gel later (gelling proteins give yogurt its texture). 

(3) Cool the water bath to 110 °F / 43 °C and let the milk cool to that temperature. You should use ice to lower the temperature of the sous vide bath quickly.

Note, if you're going to use bags, it's probably easier to heat the milk in a pot set in the sous vide bath until the milk is 185°F / 85 °C, then pour the hot milk into the Ziplock-style bags and place these into the sous vide bath as it cools.

(4) Once the milk has cooled to about this temperature, you need to add your starter culture. You can use a plain yogurt with live culture that you like for this. You don't need to add much, a teaspoon or so in each package is plenty.

(5) Incubate your yogurt for 6 to 8 hours or so. Things are going well if you get some mild cheesy aromas coming off the cultured milk and some liquid separating to the top of the gelling yogurt. 

(6) Stir or strain your yogurt depending on the style that you prefer. If you're using bags, you can just massage the outside of the bags to break up the curd. 

(7) Chill your yogurt to halt the bacterial fermentation. The longer you ferment, and the less you stir or disturb your yogurt the more tangy it will be from lactic acid forming bacteria. Chilling the yogurt slows bacterial growth and keeps your yogurt fresher for longer. 

(8) In a cold fridge (below 41F / 5C), your packages of yogurt should keep for at least 14 days. 

Does this help?

Chris