The opportunity to have a regular supply of local fresh goats milk for making yogurt, inspired me to make a simple yogurt incubator out of materials I had around the house.

Step 1: Materials and Equipment:

Rigid closed cell foam insulation
Utility knife
Duct tape
Metal ruler (carpenter's square is helpful)
Large Mason jar with plastic lid (or other wide mouth glass container)
Fabric, Needles, thread and sewing machine (optional, if you decide to make a cover)

Step 2: Measure and Cut the Box Sides

Measuring: Put the lid on your jar, and measure the width, depth and height. The 48 oz Bernardin jar I used, measured 4 1/4" x 4 1/4" x 7 3/4". Add about a 1/4" to each of these dimensions, to allow a bit of play and make it easier to get your jar in and out of the box. Measure the thickness of your rigid insulation. Mine was 1 1/2" thick.

Narrow sides: you will need two side pieces that are the width of your jar (plus 1/4") by the height of your jar (plus 1/4" plus the thickness of your insulation 1/ 1/2") - this is for the extra layer that holds your box lid in place.

Wide sides: you will need 2 pieces that are the width of your jar (plus 1/4" plus 2 thicknesses of your insulation) by the height of your jar (plus 1/4" plus the thickness of your insulation 1/ 1/2"). The sides are all the same height.

Cutting: If you have never cut SM rigid insulation before, you are in for a treat, as it cuts very cleanly and easily.

The best way to cut rigid insulation, is to make a cut with an exacto or utility knife across the whole piece of insulation in one direction (the cut doesn't need to go all the way through). Then bend the board away from the cut line, to snap it cleanly along the line.

Layout your pieces strategically on your insulation, to make the best use of your material. Use a metal straight edge, to mark and then cut your lines into the insulation with an exacto or utility knife.

Step 3: Cut Out the Bottom and Lid

The bottom of your box will be the same width as the wider sides of your box, squared.

If you don't want to measure it out, place your box sides together in position and trace around the bottom of your box on to your insulation and cut out two pieces. My bottom was 7 1/2" square.

Next, cut a square for the inner lid, with a dimension that smaller by two times the thickness of your insulation (2 x 1 1/2" = 3"), than the top and bottom pieces. My smaller square was 7 1/2' - 3" = 4 1/2" square. I angled the sides of this piece, tapering in a 1/4" or so trimming it with the exacto knife, to allow the lid to easily drop into position on top of the box and make it easy to put on and off.

Alternatively, you can keep the edges of this piece square, and make it at least 1/4" smaller in both directions.

Step 4: Putting It All Together

Assemble the sides of your box to form a square and then sit the sides on top of the bottom piece, and hold them in position with a few small pieces of tape.

Starting on the top inside edge of the box, run duct tape down along one of the side joints, with the tape centred over the joint, right to the bottom edge and cut it off. Repeat this for all four joints.

Run another strip of duct tape all the way around the box, centering the tape on the joint between the bottom piece and the sides.

Finally, centre the smaller tapered square, in the middle of the lid. Use a small piece of tape to keep it in place and then use 4 pieces of duct tape to attach it firmly to the lid (photo 4).

Step 5: Prepare Your Milk and Culture and Let It Work

You are all done your insulated box! This incubator will keep your yogurt culture in the right temperature range over the 10 hours or so, that it takes to become yogurt.

The fresh goat's milk yogurt that I made in my incubator, was delicious! But, as it turns out, the other members of my household were not as excited about the taste of either the goats milk itself or the goats milk yogurt, so my incubator is mostly an incubator in waiting, waiting for its next gig... Maybe I will make cow's milk yogurt next.

If you need directions on how to prepare the cultured milk to make yogurt, check out this instructable: https://www.instructables.com/id/No-Mess-Yogurt-Ma...

Step 6: Optional: Cover It Up

I thought that the lime green duct tape accents on the pink insulation box, although functional and flashy, might be greatly improved by a sewn cover that could be dropped right over the incubator, so I made a quick and simple cover that had a handle across the top.

Measure the height and circumference of your box, add a seam and hem allowance for the side piece and cut it out. Cut the top square, an inch wider than the top of the box, to allow for the side seam allowance.

The handle is a bit longer than the width of the box, to allow a hand to slip under it when it is on the box. Cut a 4" wide strip the length you want and fold it in half lengthways with the good sides facing. Sew it together along the edge, then turn it right side out and iron it flat with the seam in the middle of the back (photo 2). Tack the handle to the top piece on opposite ends of the top, before sewing it to the side (photo 3).

To attach the top to the sides, beginning at one corner of your square and sewing around the square one edge at a time until you return to the first corner. Sew the seam down the side and then hem the bottom edge, flush to the bottom of your box.

If you do decide to make a fancy cover for your incubator, I recommend you make the top a bit bigger than I did, so that the cover drops more easily over your box.