Monday, June 11, 2012

Yogurt Chronicle: Special Report on Filtration

One of the pieces of advice that Cultures for Health includes in their yogurt-making instructions is that if a thicker yogurt is desired, the yogurt could be strained through cheesecloth.  Thicker yogurt sounded pretty good, but really the whole thing sounded too engineer-y to pass up.  I set out to thicken some yogurt.

The first step was to spread the cheesecloth over a small bowl.  This to be a relatively strict filtration with a small fraction of permeate (i.e., the whey).  To make it even more restrictive, double-layer the cheesecloth.  Also, get a larger bowl you can pour you yogurt retentate into afterwards.
Next, pour some yogurt onto the cheesecloth.  It should be a small enough amount that you're still able to close the cheesecloth around it but a big enough amount that you have a volume big enough to filter.

This is the fun part!  Pick up the cheesecloth and let the whey drip out.  If you're doing it right (i.e., the filter is tight enough), you should get a hedgehog-like pattern of whey droplets on the outside, which will then fall into the bowl.  You might need to squeeze it to help it filter, but don't squeeze too hard because it tends to open the pores of the cheesecloth and let too much yogurt through.
Here's what some whey looks like once you've filtered it out.  There's not much of it, but you can improve the separation with a multi-stage filtration.

Now, pour your yogurt into the larger bowl.  It's thick and ready to eat!  If you choose to pursue the "filter it again" method, be sure to get a fresh piece of cheesecloth because it's likely your cloth's pores have opened during the filtration.  With larger holes in the filter, more yogurt gets through, and you don't end up actually thickening it.

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