Sunday, November 29, 2009

+1 for Liquid Tape, or What Happens When You Forget to Put the Heat Shrink On Before Soldering

I'm starting to put together some new temperature probes. The experience reminds me why I don't do work that requires fine motor skills. Also, it's fortunate that the solder connections are hidden away because I'd have to turn in my nerd card if they had to pass inspection.

The probes I have, containing Dallas Semiconductor DS18B20s, were soldered for me by my friend and Triple Mutt Brewery founder Chuck. (He's getting into the brew controller business himself - watch this space for details.) The probes work fine with my Arduino-based microcontroller and they have become an essential part of the brewday experience, but my continuing frustration with dealing with the serial I/O aspects of that board have taken me in a different direction. I was introduced to the CAI Networks WebControl board by a thread on and it looks like it might be just the device to eliminate my communication challenges.

The challenge I discovered upon receiving the controller is that my existing probes, which are wired for for the "parasite" operating mode of the DS18B20, won't work with the WebControl's OneWire connection port. The board is set up to expect the Dallas Semiconductor devices connected to it to be wired for normal, powered operation. There's no way to correct the manner in which the existing probes are wired, since they are potted into some excellent stainless steel probe ends from, so I am building some new ones with the powered wiring configuration.

I soldered the first of the set yesterday, and this post's headline is a little misleading: I omitted the heat shrink on purpose. I found that I had some difficulty getting the sensor and wire all the way to the bottom of the probe end when I assembled the first set of probes, and that was partially due to the combined diameter of the heat shrink and cabling. It was a very tight fit and frankly I'm not sure I actually got the temperature sensor all the way to the end of the 8" probe, so there might be some dead space in there that slows down the temperature transfer rate from the outside to the chip. I decided this time to omit the heatshrink tubing in favor of the conformal coating insulation provided by Liquid Tape.

There are lots of brands of Liquid Tape available. I used the one I found on the electrical aisle at Lowe's. I'm not particularly worried about it being food-safe or having high heat resistance because it's going to be sealed in the probe end and won't be exposed to the environment. I'm going to use some heatsink compound to ensure a good thermal bond between the stainless and the temperature sensor, then seal around the cable exit with J-B Weld.

One tip: the applicator in my Liquid Tape can was nigh on to useless for getting a good coating of rubber on the leads of the DS18B20. To get a reasonable result, I ended up just making a puddle of Liquid Tape on a paper plate and dipping the assembly's wires into it, letting the excess drip off each time. After a few dips, a 10 minute curing rest and then a few more dips, I had a reasonably uniform thin coating on each connection.

Brewed: 091103 Por Favor - 10 Gallons

As I suspected, the second 10 gallon batch was more straightforward than the first one because I knew what to expect.

When I did the first ten gallon batch I neglected to mention that I initially missed my target mash temperature - low - by a lot. I tried to heat the mash using a heatstick and was eventually able to get it to the right temperature. It was a PITA because I was afraid to leave the heatstick alone, fearing scorching, so I had to constantly stir the thick mash.

I did a post-mortem evaluation of the whole "how hot should the strike water be" thing to back-check the calculated value from BeerSmith. Using the calculator at Brewer's Friend I was able to confirm that the number that BeerSmith proposed was supposed to be correct, even after correcting for a lower than documented grain temperature. Somehow, though, that number wasn't translating into the right mash temperature. I suspected that there was some feature of the mash tun that was sucking the heat out of the water before it could be transferred to the mash.

For this batch, I heated the strike water to 5 F higher than the recommended value and let it sit in the tun for 5 minutes to pre-heat it. Upon examination, I found that the water temperature had dropped to 160 F. Fortunately I was ready with a heatstick, and I used it to raise the water temperature in the tun back to the required value before adding the grain bill. The mash came out right on target when I measured it. A HERMS is moving up the priority list.

I noted that the sparge water requirement was a logistics issue when I wrote about the first 10 gallon batch. Knowing this, I addressed it head-on by using two smaller pots to each heat half of the 10.2 gallons of sparge water required. Just after the mash started, I stuck a heat stick in each pot. This raised the water from ambient (around 60 F) to somewhere in the 110 F range, and as the time to sparge approached, I put one pot, with heatstick, onto the propane to raise its temperature to 168 F. While I sparged with that pot's water, I moved the other pot onto the burner to raise it to sparge temperature as well. That strategy worked great, but 5 gallons of hot water is still a lot to hoist up and dump into the mash tun. An electric HLT is moving up the priority list.

Por Favor's recipe has a larger grain bill than Geordie-Boy, and I very nearly reached the top of the big mash tun with this batch. There was only about a 2 inch headspace left after the sparge water infusion. I need to keep that in mind as I plan new brews.

Luckily, Scotty was home again so I had help transferring the 14 gallons of wort to the burner. With two heatsticks and the burner I got my rolling boil and everything went well thereafter. I scooped off most of the hot break foam in an effort to reduce boilover and clarify the wort before it went into fermentation.

Cooling wort has become increasingly easy as the water and ambient temperatures go down. I think it was less than 15 minutes before I got the wort down to below 80 F, where I put it into carboys and let it sit for a couple of hours to finally hit pitching temperature. (I had to leave for a basketball game or I would have spent the extra 10 minutes to get it down to 60 F with the immersion chiller.)

The gravity for this batch came in at 1.058, which was again higher than the estimated 1.051. I am looking forward to kegging this in a couple of weeks. Speaking of which...

Kegged: 091101 Geordie-Boy

This was my first 10 gallon kegging, and I was able to interleave it with my other brewday activities. In fact, I racked a carboy during each of the sparge cycles for the Por Favor batch. The final gravity for this Geordie-Boy was 1.012, which puts it at an ABV of 4.43%. I'm liking the attenuation of the Nottingham yeast. The sample was good, let's see how the beer tastes when I carbonate one of the two kegs today.

That leads to an interesting point: I don't have room to chill both kegs, or any more kegs for that matter. The second Geordie-Boy keg will be aging at "cellar temperature" in the garage for a while. I wonder what affect that will have on the flavor. A beer cave is moving up on the priority list.

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