Sous vide burgers

Quick on the heels of upgrading my sous vide controller last week, this past Sunday we had some friends over for a "barbecue" where I made sous vide burgers. The recipe was "simple," it only had two ingredients:

1. grind up a bunch of meat (sorry, didn't take any pictures of this)
2. add an amount of salt equal to 0.8% times the weight of the meat
3. shape into 160g patties, seal in bags (with about a teaspoon of oil [fine, three ingredients]) using the water-displacement method, and let sit in the fridge for an hour
4. cook sous vide at 131F (55C) until burgers reach a core temperature of 129F (54C)
5. sear on grill or with blowtorch
6. eat!

Here are all the burgers cooking:

Although it looks like the temperature is actually 2.2 degrees too hot, I haven't fixed the offset on the PID yet. It's actually at 55C.

The final result, perfectly medium-rare through and through, on a bun with mustard, tomato paste and vidalia onion: