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 fire.tc.faa.gov 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.

Temperature Controller

I spoke previously on here about adding a temperature controller to my Black Garlic Oven design, and appreciated CubeConvict's recommendation of the STC-1000. I found this general use controller intuitive in ways, though the software interface is somewhat erratic in its utilization of its buttons.

To illustrate this, consider the hardware connections on the rear of the unit. The connections are all screw terminals, with pairs for power, sensors, cold and hot, in that order. I found this configuration straightforward and appropriate the the application. The software interface, however, offers challenges. The power button is labeled with a standby symbol, which alone is confusing. Furthermore, consider the way to change temperature. On the main screen, one holds the "S" key for 3 seconds, selects a menu item using "S" and then adjusts the setting by holding "S" and pressing "Up" or "Down". When the desired setting has been reached, one presses the Standby/Power button to commit the change.

Thankfully, the unit required very little adjustment. For housing, I purchased a PVC box (As pictured in this MakeProjects post) and added a power outlet and binding posts for the sensors. After splitting the plugs on the power outlet, the unit allows me to simply plug the oven into the "heat" plug.

The binding posts and banana jacks purchased from RadioShack, with the binding posts being advertised as "insulated" (though it would take a far stretch of the imagination to consider these meaningfully insulated). The binding posts are screw-on, and I drilled holes to attach the power outlet. The STC-1000 has mounting brackets included that secure it to the lid. I used disconnect terminals inside to attach the power cord to the controller and the outlet (the electrical tape wrapped bit connection the end of the power cord's sheathing), and spade terminals to provide power to the outlet.

Everything fits easily inside the 4"x4" PVC box that I purchased from my local hardware store. To secure the power cord inside the box, I put two zip ties on the cord and heat shrink wrapped them with a glob of glue inside the tube.

Part of the beauty of this controller is that, in an arrangement such as this one, it can be used to control both heating elements and cooling systems (such as an AC or a chest freezer), allowing it to be used for any application between -50°~90°C. I will likely use the STC-1000 for many other fermentation chambers in the future.

Update (2013-01-07) - Circuit Diagram:
A barebones illustration of the circuit with a heating incandescent and cooling appliance plugged in.

Garlic Amino Salt

Taking a cue from Chalt, I decided that I should like to make an amino heavy salt. I have previously been led to believe that the flavor advantage of sea salt, particularly highly regarded sea salts such as sel gris, fleur de sel and varied other examples, is the mineral and amino content imparted by the brine from which it is collected. My intention in this case was to create a reduced salt with far-increased amino content, intended to be used in a similar way to soy sauce, but without the addition of liquid. I'm calling this salt "Garlic Amino Salt", as its ingredients are sea salt, alderwood smoked salt, black garlic powder and minced preserved garlic.

As this is a small-batch experimental recipe, I started by adding 250 mL of Spring Water to a medium saucepan over high heat. Once the water started boiling, I reduced the temperature to medium, and added 50g of an ordinary, mid-price Sea Salt.

I then began attempting to super-saturate the solution with sea salt. After adding 25g more salt, I discovered that the solution was too thick, and added 100mL more water. The solution at that point seemed too thin. I then added 3g of smoked salt and 5g of sea salt, and started adding water in 15mL increments. After 5 such increments, I decided that the solution was appropriately dilute as to be supersaturated at boiling. I then added the black garlic and minced garlic, boiled for 2 minutes more, and poured the mixture through a plastic filter I purchased online into a 2.2qt Pyrex baking dish. It was then placed in an oven at 275F, as shown.

I checked the solution at 15 minute intervals, observing the drying taking place from the outer rim of the dish inward, as illustrated in the following sequence. Note that significant precipitation happened in the first 15 minutes of the process.

After 90 minutes of such, I found that the solution had dried into a loose cake. I removed the dish from the oven and stirred it using a silicon spatula. The resulting aggregate was semi-moist, with pockets of completely dry salt interspersed. I decided that the mixture could use more drying and placed it back in the oven for another 30 minutes.

At this time, I removed the salt from the oven and stirred it up once again. It had become dry throughout, excepting a few small, moist clusters that nonetheless crumbled between my fingers. Tasting the new salt, it was intensely savory, with a significant but far-reduced saltiness from the original sea salt. I think it would work well as a salt replacement at anywhere from 1:1 to 1:2.5, for any recipe that the cook wanted to make more savory and wouldn't mind including black garlic flavor.

I believe this recipe would be helped by the inclusion of a vacuum hood for the reduction of the salt, coupled with a significant reduction in drying temperature. When using a vacuum hood, however, I would double the black garlic content and remove all minced garlic. The inclusion of some (5g on the light side to 15g on the heavy side) dried roasted garlic would be preferable to minced garlic in this case.

This experiment had an unexpected but not altogether unwelcome side effect. On a first attempt, I accidentally added the garlic and black garlic early, and decided I should start over. Not wanting to waste perfectly good black garlic, I put the failed recipe in a Pyrex loaf dish in the oven, without filtering, and the garlic mixture reduced down to a thick paste. I intend to put it in a yet undetermined amount of olive or canola oil, and use the result as a cooking paste or condiment.

Experimental data was transcribed to a text file, available on Google Drive.

Sweet Potato Syrup

There is an old article from 1920 about the existence of diastase in sweet potatoes. Diastase is a general term, referring to enzymes that facilitate the decomposition of various polysaccharide starches into maltose, a disaccharide. As I understand it, sweet potatoes contain a substantial amount of beta amylase, and a small amount of alpha amylase (the content increases with aging). The above linked article refers to an older process determined by the US Department of Agriculture (I have not been able to find the article on their site) for making sweet potato syrup using malt, for its alpha amylase content. This is my second foray into sweet potato syrup production, and it went much better than my last time.

I started with 10 large sweet potatoes, acquired from my local grocery store. I am not sure of the weight of the purchase, as I was going to record it from my receipt from the grocery store, but I managed to misplace the receipt. I took each potato and cut it into four pieces length-wise, and then cut those wedges into individual quarter-slices, as shown below.

In the 1920 article, they talked about using shredded sweet potatoes or sweet potato flour. While I think that the shredded sweet potato would have worked well (as well as saving my poor thumb, the tip of which I cut off while I was chopping sweet potatoes), I think that flour would have made filtering an enormous hassle. The quarter-slices worked well, however, yielding two large bowls of slices.

Endeavoring to follow the paper's steps somewhat, I decided to roughly follow their process, which seemed to work pretty well. I added the sweet potatoes to the pan with water to cover (I added a little extra water, which I'll comment on later in the article), and started heating up the mixture over medium heat.

After fifteen minutes of heating, I checked the temperature on the electronic thermometer, for which you can see a bit of the sensor and its wire in the above picture. The temperatures were recorded during heating as follows:

Temperature Fahrenheit (T) at time elapsed in minutes (t) with stove heat setting (Q)

Mins.	°F	Heat
15	157	5
30	160	1
70	180	3
80	189	5
90	197	5
100	208	5
105	210	5
110	212	5

After boiling, I mashed the sweet potatoes using a potato masher. This was complicated by the fact that there was more water than I had intended, which meant that it was harder to be sure that all of the chunks were processed (many weren't). I used a four step process to extract liquor from the pulp, and it still wasn't as effective as I had hoped. My steps were, in order, to sieve using a chinois and pestle, to filter through a metal mesh coffee filter, to filter through paper coffee filters and then to reduce in the oven overnight, as illustrated.

It's not easy to see in the last picture, but the syrup that has been filtered through paper coffee filters still has a fairly small amount of sweet potato pulp in it. I set the oven at 220°F and let the syrup sit for about 8 hours. When I checked it, it was much sweeter, and had reduced by about half.

I intend to improve the process in the future, and I have some very specific ideas for how to do so. Instead of integrating the enzymatic action and heating to boiling, I'll use water to cover heated to about 170°F. After adding the sweet potatoes, I'll put the whole concoction in my (now temperature controlled, more about that in a later post) light bulb oven, and let it convert for about 2 hours. I'll then boil it on the stove and, instead of mashing the pulp and sieving it, I'll remove most the water by straining, and then use a hand blender to process it into a paste. I'll then create a large filter by putting a piece of wool felt over the top of a bucket, with the cut off top of another bucket holding it in place. As I understand it, wool is better for filtering syrup, as it doesn't clog as easily and filters more thoroughly.

Next time I do this, I'll likely also use malt in the mixture. My intention is to make a simple sweet potato beer and, since sweet potato doesn't contain the necessary amino compounds to support yeast fermentation, malt is necessary for the conversion into beer. This sweet potato and malt beer will then be converted into vinegar, to be used as the base for a Worcestershire-like sauce, possibly tomato-based, that I'll be making.

Black Garlic Sauce Update

Since my buddy was in town for the weekend, and I was sending some of the sauce back with him, I went ahead and further processed the sauce. I added some onion powder, garlic powder, black pepper, dried mushrooms and anchovy paste, and then used a hand blender to puree the mixture. After blending, I let it sit for a couple of hours, at which time the mixture had gotten smoother and sludgy. I added 1/2 C of good Fish Sauce, 1/2 C of passable Dark Soy Sauce, and a further 1/2 cup of Michiu. I intend to give the sauce about a month to age, at which point I will see how it has turned out.

If you noticed that the level should be higher, that's because it should be. I sent my buddy back with about 10 oz. of the sauce in a Topo Chico bottle, which he has been instructed to cover with foil instead of the cap with which I sealed it.

The Black Garlic Oven Post

Today, I harvested my last batch of black garlic and, having pre-harvested one head and having taken four for the sauce base, processed the last seven heads, cutting half up to dry for making black garlic powder. The remaining half will be used at-will for recipes, etc., with some going to a buddy of mine. I've also started a new batch for next month, which I'll cover later in this post. First, I'd like to explain how I made my light bulb powered black garlic oven, using the Huskee Tough Guy EPS (expanded polystyrene) cooler, as somewhat pictured below.

Expanded polystyrene is recommended for applications below 160 degrees Fahrenheit, with this one coming in about 10 degrees below that mark. I started by covering the walls with aluminum foil, reflective side inward-facing, securing it with normal Elmer's Glue-All. I then drilled a 1/2" hole in the bottom center of the container, through which to pass the wires for the light bulb. The tiles were positioned in a diamond shape in the bottom, as depicted here:

The tiles have small felt feet on them in the form of a flattened "X", with top and bottom one inch in from the edge of the tiles. This keeps them from scratching the aluminum foil, while providing a solid base upon which to place ball jars, with enclosed garlic. While I have used ball jar canning lids in the past, I have decided to switch to aluminum foil as the exclusive lid, as it doesn't need to be a perfect seal and I'm concerned about the BPA content of the canning lids. I have placed the reflective side up, as below:

Note the stone filled jars from the last post. They provide IR absorption and thermal mass for the system. As a strongly IR absorbing material, stone also emits IR, bolstered and buffered by the high specific heat of the water. In my other experiences with fermentation, I have understood that light exposure can be detrimental to the fermentation process. Googling "Light effect on fermentation" seems to provide a number of articles, blog entries, &c. that suggest that both visible light and UV radiation can have a negative effect on fermentation. I genuinely don't know if they apply at 140°F-150°F--a perceived consensus indicates this range for black garlic (per this instructable and this make article)--but this mitigates the issue, while the dry heat resists mold and non-beneficial bacterial growth.

Each head is placed in an individual 8 oz. ball mason jar. Some of those that I have are normal and some are quilted, but I don't think it really matters which one is used, save the utility of having the measurements on the side of the normal ball jar. I leave the heads sealed in the jars for 30 days, at which time I remove the lids and let the garlic dry. This results in cloves that are dark, textures and have shrunk away from the skins of the garlic. Some in the last batch were drier than others, with some reducing to a powder when pinched between the fingers, while others were leathery and pliable. The harder examples were cut up and reserved for additional drying, for making black garlic powder.

To measure temperature, I punched a hole in the side of the cooler using a small meat thermometer, calibrated in boiling water (e.g. This Taylor product) around the middle of the height of the jars. Using this to monitor temperature, I used a number of different light bulb wattages.

 I found that I had to use 40W bulbs during higher Central Texas summer garage temperatures, and a 30W bulb during lower temperatures. The incandescent bulb needed will vary by ambient temperature, but I would wager that 40W is a reasonable base starting point for most room temperatures. I conducted primary research with a nominal quantity of water in the system (and no garlic) monitored by a webcam. I will provide the records from this experimentation in an update to this post.

For reference, I used a ceramic light socket I got from a cheap lamp I bought from Lowe's hardware store. There is one very near my home, and I found that they have ad hoc porcelain light sockets for between $3 and $4. I used a cord from another, broken appliance, and soldered some fork/U-shaped terminal connectors to the end of its wires. I bought the cooler at Academy, and I can't easily find the price, though I believe it was no higher than $30. Altogether, I remember calculating (some time ago) that the apparatus, plus electricity, with initial cost of garlic was less than the cost of twelve heads of black garlic online. For the record, this is an excellent use of incandescent light bulbs, as they put off far more heat and IR radiation than light. In the month it takes to do this, the oven costs on the order of $5-$8 per batch, including electricity and garlic, but not including the cost of manufacture.

Black Garlic Sauce Base

Early this morning, I chopped up some black garlic into a mix of 1 cup of Kikkoman light soy sauce and and 1/2 cup of Michiu, as seen below.

I used four heads' worth of black garlic cloves in the sauce. My intention is to store the sauce in the refrigerator for a week, and then blend up the sauce base, while adding some onion, garlic, anchovies, dark soy sauce, fish sauce and (possibly) ginger. I plan to then store the sauce in a sealed container in the refrigerator for a further few weeks, at which time I will test the sauce to see how it tastes. 

The sauce is meant as a cooking ingredient or base for another sauce. I fully expect that it will impart significant savoriness, or umami, to the dishes in which it is added. 

I also put some rocks in jars tonight. In my current black garlic oven, I have four pint jars full of water between the light bulb and the garlic, to provide the system with some thermal mass.  In thinking that I'd rather the heat be a little more even, I reckoned that stone absorbs IR radiation, so the addition of rocks with  water should deliver more even heat throughout the oven while protecting the garlic from direct light. The jars are pictured below.

I'll next post a detailed guide to the structure and setup of the black garlic oven, when I load it with garlic this Saturday, following the harvest of the black garlic currently finishing its drying process.