Cooking For Engineers

[OldScienceTeacher]

New guy here - happy to find kindred souls.

I built a sous vide controller and am using it with a deep fat fryer (9" diameter or so, about 10" tall, perhaps) and no circulation method (yet).

The local market is now selling vacuum-packed meat, and I bought some soon-to-outdate cuts (a standard trick for us).

I've done four or five of these packages (flank, chuck, or brisket, 1-2 days at 131 degrees). Some turned out great, but two of them blew up like balloons. I opened one of them (a mistake): the meat had gone waaay bad, causing the gas generation.

I used a meat thermometer last night to check possible excessive temperature variation. It appears that while the sensor is accurately keeping its tip at 131, the top of the water is more like 120 degrees. Is that my problem, solvable with proper water circulation?

I have a stirring bar on order, and intend to build a variable speed motor to put underneath the cooker, using hard drive magnets to spin the stirring bar through the aluminum.

Thoughts?

[Michael Chu]

The minimum safe temperature for long cooking in a water bath is typically 131F. Theoretically, the threshold is closer to 127F as Clostridium perfringens continues to grow at 126F and most other pathogens (salmonella, listeria, e. coli) stop growing / start dying around 123F. However at such low temperatures it takes a LONG time to kill off the pathogens and the meat may not be safe to eat or could be spoiled due to that length of time. So, 131F is probably as low as you want to go because in most cases the pasteurization time is reasonable. Since the top of your water bath is only 120F that's a dangerous spot to be in. You are either filling the bath too full (or covering the bottom where the heating elements are and preventing natural water flow) or you will need an active system to circulate the water. Sometimes just setting up a wire rig to hold your bags upright will help moderate temperature. Also, if your cooking vessel is very deep (much taller than the base is wide) then you will get more temperature variation from top to bottom without adequate circulation.

Also, there is also the chance that your themometer's readings can be uniformly inaccurate and the actual water temperature might be a degree (or more) off from your readings.