Wednesday, February 13, 2013

Repurposed Cardboard Black Garlic Oven (Part 1) & Sous Vide Project Failure

I've started work on a second model of my black garlic oven. This design has a vertical chamber to increase the amount of garlic that can be held. My target capacity is thirty-six jars arranged on four shelves, with a heating bulb on in the bottom of the unit. Having the bulb on the bottom of the unit should encourage passive convection, since the top of the chamber is where heat will most easily collect and leave the system. As hot air from the bulb travels upward and cool air  from the ceiling travels downward, some convection should occur.

From a materials perspective, I reckoned that the expanded polystyrene insulation of the first design was excessive. This time, my primary materials are cardboard from shipping boxes and packing peanuts. This document at indicates (in table 1) a mean temperature of 612 °F with a lower bound at 575 °F, both temperatures well above (likely more than double) what this system will encounter.

As depicted in the picture, I used starch glue to make a four-layer shell. The recipe for my starch glue was 100mL of starch in the above-pictured pyrex cup with water to 500mL in the cup (also, I understand that 1 Tbsp. of salt added to the mix will discourage mold growth). I then microwaved the stirred mixture in thirty second intervals, stirring between, until the mixture thoroughly gelled. The benefits of this glue are low price (since a full recipe uses a trivial amount of corn starch), high bonding strength for paper and a stability in heated environments. I used a grooved trowel to apply the adhesive to the cardboard, and held the glued surfaces together using bar clamps and some surplus cheap flooring strips I had available, as pictured below.

The starch glue dries quite slowly (a number of hours), so the assembly of the four layer box took almost a week. The finished shell is stable, fairly rigid, and about three quarters of an inch thick, as pictured standing below.

In part two of this project, I will add spaced extensions to the shell, to be filled with packing peanuts and scrapped expanded foam. With the three inches of combined insulation (of various effectivenesses), I anticipate a total R-value of R-5 ‒ R-9, which seems ample if energy conversation is the goal.

The "Sous Vide Project" mentioned in the subject of this post was a series of projects I had planned (at an elevated expense relative to my other projects) to construct, from scratch, a water oven to be used for sous vide cooking. I planned to pump water from a high-temperature plastic chafing dish to a deep metal dish containing a heating element. I purchased most of the equipment needed for this venture, and all but the chafing dish and pump arrived (coincidentally, the two most potentially costly items), the dish because the price quoted on the site was wrong (I should have known that half price was too good to be true) and the pump for reasons yet to be determined (but I have been unable to get a response from the seller).

Because the chafing dish I intended to use is normally expensive, and since the pump was the only reasonably priced example I could find on the internet, the project series has been scrapped. I offer this as an explanation for the sizable interval prior to this post, fully unintentional as it was. I will likely buy a consumer water oven at in the near future for sous vide use, and am particularly eyeing the Sous Vide Supreme.