Insulation for Single Vessel Brewing
The wisdom among all-grain (and partial mash) homebrewers is that you want to hold your temperatures as steady as possible for each step of your mash. Meanwhile, the desire among single-vessel brew-in-a-bag (BIAB) brewers is to keep the process as simple as possible and the gear to a minimum. As just such a brewer (all-grain, single-vessel BIAB), that was the challenge in front of me: How do I hold a reasonably steady mash temperature while staying true to my goal of single-vessel simplicity?
My friend Aaron Ritchie (you may remember him from the March-April 2018 Brew Your Own article “Big Batch BIAB”) suggested that I try using Reflectix insulation (which we lovingly refer to as “battle armor”) to help meet that challenge. It’s relatively inexpensive; it’s durable enough to easily last dozens, if not hundreds, of brew days; and given that it was designed to insulate houses and ductwork, why wouldn’t we give it a shot?
Importance of Mash Temperature
First of all, why is a steady mash temperature important at all? I won’t pretend to be an expert, but I’ve read a lot, so I’ll turn to my bookshelf.
In The Complete Joy of Home Brewing 3rd Edition (2003), Charlie Papazian writes:
The time it takes to fully convert starch to dextrins and fermentable sugars varies with temperature, amount of enzymes and amount of starch to be converted.
Generally, higher temperatures will inspire quicker conversions but will produce more dextrins.
Then there’s John Palmer, who in How to Brew (2006) notes:
Each of these enzyme groups can be influenced by different temperature and pH conditions. However, enzyme activity is usually more dependent on temperature than on pH. You can adjust the mash temperature to favor each successive enzyme’s function and thereby customize the wort to your taste and purpose.
Gordon Strong asserts in Brewing Better Beer (2011):
One of the biggest misconceptions about enzymes is that they work like transistors or diodes — that they just switch on or off under specific conditions. Don’t think of it as a switch, think of a bell curve — there is a region where the enzymes are most active, but they are still functioning outside the prime temperature range. However, once enzymes are heated beyond their normal functioning range, they begin to denature (or break down), an irreversible process.
Putting these bits of knowledge together, we can conclude that temperature matters because:
1. It has the most significant influence over the activity of different enzymes.
2. Letting the temperature get too cool can slow the activity for certain critical enzymes.
3. Letting the temperature get too hot can start to denature those enzymes, slowing or even halting their activity altogether.
In other words, let the mash temperature drop too low and alpha amylase isn’t working as quickly as you expect; start too warm and run the risk of denaturing too much beta amylase before it has had a chance to work. In both cases, there’s a risk that you might not get full conversion. In the former case, you might end up with wort that’s more fermentable than you expected, lowering the final gravity and increasing the strength while decreasing the body. In the latter case, you might wind up with a more dextrinous wort with a higher-than-expected final gravity and thus more body and a lower ABV.
Or even more succinctly: If you can’t hold a steady temperature, you won’t end up with the wort you wanted, and therefore might not get the beer you wanted.
Mash Temperature Control Methods
Before jumping in with the Reflectix, we should consider what other methods are out there for controlling mash temperature in a single-vessel BIAB system.
The obvious first response is: “Why not just use a dedicated mash-lauter tun (MLT)? Something like a converted picnic cooler with a false bottom?” And to that I would respond that that’s a great idea! Except for the part where I’m trying to keep my process as simple as possible and my gear to a minimum. There’s nothing wrong with an MLT, it just doesn’t fit my brewing style. (I’d rather save money on gear so I can spend it on ingredients.) But stating this up front helps to put a ceiling on how complicated (gear-wise, at least) we want our mash temperature control process to get — in other words, no RIMS (recirculating infusion mash system) or HERMS (heat exchange recirculating mash system) in this list!
Bath Towels
If we’re talking about simplicity, then it doesn’t get any simpler than wrapping the kettle with a couple of bath towels. This is where I started when I did my first partial mashes on the stovetop. I would grab two or three towels from the bathroom closet and, after mashing in, drape them over the kettle. Typically, I would cinch the towels with bungee cords to keep them snug.
The pros here are that you’ve almost certainly got a couple of bath towels lying around; simply re-purpose them for an hour or two on your brew day. As an added bonus, you’ll now have those towels handy to help with any cleanup as the day progresses.
The cons are that the towels themselves are not great insulators. Looking over my brew day notes from that period, I would lose on average of 6–8 ºF (3.3–4.4 ºC) per hour during the mash. This is better than heat losses from a naked kettle, but it’s hardly great. Also, towels are flammable, so if you’re not careful they can present a fire hazard.
Kettle Cozy
Another option is to build a kettle (or tun) cozy like the one James Gilbert described in the December 2015 issue of Brew Your Own (or online at https://byo.com/project/keep-mash-tun-insulated/). Gilbert’s method is to use insulating expanding spray foam to create a custom-fit removable shell for the kettle. I won’t go into the details of the build here, but suffice it to say that he claims the project can cost as little as $25 and you can bang it out in a couple of short work sessions (plus the 24-48 hours of waiting while the spray foam sets and cures).
Reading Gilbert’s article, there seem to be a number of pros here. First, after the build, you end up with a sturdy and reusable insulated shell that is the perfect size for your kettle. Second, the spray foam has good insulating qualities and can restrict overall heat loss to approximately 4 ºF (2 ºC) per hour.
On the cons side, the shell is somewhat bulky, so if storage space is at a premium, this may pose a challenge. Also, while Gilbert describes the project as fairly easy, I’m going to once again invoke my laziness and say: “Looks like too much work for me.”
Multiple Infusion Mash
If you have an extra kettle and heat source, you could try to hold the mash temperature through multiple infusions over the course of the mash. If you’ve ever performed a step mash then this technique is similar. You start your mash at a known temperature and, with an idea of your heat loss over time, make subsequent infusions of hot water at set intervals to raise that temperature back up to the desired range. Where this technique differs from the step mash is that you are not performing multiple rests at multiple different temperatures; instead you are trying to stay as close as possible to your target temperature for as long as possible.
For example, if you are trying to hold a mash temperature of 152 ºF (67 ºC) for 60 minutes, you could make infusions after 15, 30, and 45 minutes in an effort to maintain that temperature. For example, on my system, I might calculate a total of 30.16 qts. (28.54 L) of water needed for the mash, and I might expect a naked kettle to lose 10 ºF (5.5 ºC) over that hour. I could knock back the initial infusion to 18.16 qts. (17.19 L) and add 4 qts. (3.8 L) at 162.5 ºF (72.5 ºC) after 15 minutes, then another 4 qts. (3.8 L) at 164.5 ºF (73.6 ºC) after 30 minutes, and lastly 4 qts. (3.8 L) at 166.5 ºF (74.7 ºC) after 45 minutes.
There are a couple of pros to using this method. First of all, if performed with precision, you can hold your mash temperature to between 1–2 ºF (0.6–1.1 ºC) for the duration of the mash. Another potential upside is that you can take advantage of a thicker mash, particularly in the early stages of the mash schedule. The other pro is that, depending on your system, you probably already have a large-enough kettle left over from your early brewing days, and your stovetop is likely powerful enough to heat the volume you need in the time you need.
This method isn’t without its cons though. First of all, though you probably have that extra kettle, it’s still another piece of gear to wrangle. Second, be prepared to do a lot of math. Even if using homebrew software, you need to figure out how much water you need for your mash overall, make some choices about the size of each infusion, and do some guesswork around what the temperature will actually be at each of those intervals. Therein lies the third wrinkle: It might be difficult to predict just what the mash temperature will be at each of these intervals. The temperature loss isn’t necessarily linear, and is influenced by a number of factors that include (but are not limited to) the material of the mash tun, whether you’re using insulation, how much headspace is in the tun, what the liquor-to-grist ratio is, and what the ambient temperature is. As a result, you wind up having to either place faith in your guesses and ride it out, or else take temperature measurements with each infusion, plug them into your calculator, and adjust on the fly. And that’s assuming that your heat source can keep up with demand. And that you’re not making mistakes along the way.
Having tried this method a couple of times, let me just say that it’s not for the faint of heart.
Periodic Direct Heating
In the same vein as the multiple infusion mash method, you can periodically apply direct heat to your kettle with an eye toward holding the temperature in the right range. The general idea is that, as the mash progresses, you would stir to homogenize and sample the temperature at intervals. If the temperature is holding within a certain margin (e.g., 1–2 ºF or 0.6–1.1 ºC) then you just leave it alone until either the next reading or whenever you can reasonably predict that it will go out-of-band. If it the mash does fall below the threshold, then you would apply direct heat to the kettle, stirring the whole time, and then shutting off the heat when the temperature gets back to its target.
This method has a couple of items in the pros column. First, it doesn’t require any additional gear. You’re using the same kettle, heat source, thermometer, and stirring utensil that you did when you mashed in. Second, with knowledge of your system and attention to the heat, you can hold those temperatures within a couple degrees of your target.
Of course, as with all of these methods, there are a couple of cons. The biggest potential con is the risk of scorching your grains or having your grain bag “fuse” to the bottom. Either of these events could ruin a batch — either by imparting inappropriate burnt flavors or destroying your brew bag (and maybe your kettle) in the process. This method also takes nearly constant monitoring of your mash. The other major con here is that, unless you know your system very well, applying the direct heat is still a bit of a guessing game. Is one minute of heat enough? How about two? How quickly does your thermometer update? Did you accidentally overshoot the target temperature by a degree or two? Or more? Lastly, if you are using some kind of insulation around your mash tun, this method translates into tedious “undressing” and “redressing” with each application of heat — otherwise you wind up burning the insulation in the process.
I’ve used this method many times, and while I can say confidently that it works, I can also say that it’s way more tedious than I want for my brew day.
Enter the Reflectix Insulation
Seeking that happy medium between effectiveness and simplicity, I turned to the Reflectix insulation. As mentioned earlier, the material is designed to insulate homes, ductwork, hot water heaters, and other objects where heat loss is a concern. I picked up 25 linear feet (7.6 meters) of the 24-inch (60-cm) wide Reflectix at my local hardware store for about $25. It’s quite a bit more than I needed, but this way I could fashion insulated wraps for both of my kettles.
Creating the Reflectix battle armor was easy. Here were the steps I took:
1. Get your kettle dimensions. You’ll want to know the height and the diameter. From the diameter you can derive the circumference.
2. Roll out Reflectix equivalent to the circumference, then maybe add an inch or two to give yourself some buffer. Cut this off of the roll.
3. Using the height of the kettle, mark how much Reflectix you need to cut off. I used a long straightedge and a permanent marker to draw a line, then I just used a pair of sharp scissors to trim the excess. A utility knife would work equally well.
4. Hold the Reflectix up to your kettle and start to wrap it around. You will want to use the permanent marker again to mark where the handles are. Use the scissors or utility knife to cut slits for the handles to poke through. For best results, cut the slit for the first handle before continuing with the wrap and marking the second. Optionally, if your kettle has ports, mark and cut gaps for these as well.
5. Roll out some more Reflectix, this time at least equal to the diameter of the kettle. Place the kettle lid on top of this stretch and trace the lid with the permanent marker. Once again, use the scissors or utility knife to cut out the insulation.
6. Place this circle of insulation on top of the kettle lid and mark where the handle is. Use the scissors or utility knife to cut a slit for the handle to poke through.
7. Double-check everything to make sure it fits around the kettle. If you have enough overlap, you could use Velcro with adhesive backing on the Reflectix to hold it together. Otherwise, just wrap a couple bungee cords around
the kettle.
Voila! Now we have our custom-fit “battle armor” insulation ready for brew day.
Does It Actually Work?
I’ll admit that when I first made my “battle armor,” I just took for granted that it worked. In other words, I assumed that because I used a material designed for insulation, that it would hold the mash temperatures pretty darn close to target.
But when I did my first mash with the Reflectix on, I noticed a loss of about 5 ºF (2.8 ºC) over 60 minutes. This was better than when I’d been using the towels but not quite the improvement I expected. The second time I used the Reflectix, I noticed that I lost 4.4 ºF (2.4 ºF) over 60 minutes. I continued to track these temperatures (like I always had) over the next couple months, and saw the trend was that I lost somewhere in the vicinity of 3–5 ºF (1.6–2.8 ºC) per hour — not what I’d hoped, but better than the 6–8 ºF (3.3–4.4 ºC) I had been getting with towels on the stovetop.
Finally, I decided to put this to the test and devised a little experiment with seven steps.
1. I would fill my 10-gallon (38-L) kettle up half way with 5 gallons (19 L) of water.
2. I would heat the water to 150 ºF (65.5 ºC).
3. Every 15 minutes I would perform 10 seconds of stirring to homogenize the water, then record the temperature.
4. After 60 minutes, I would record the terminal temperature.
5. I would do this with a “naked” (i.e., uninsulated) kettle.
6. And again with a single layer of Reflectix.
7. And then again with a double layer of Reflectix.
I chose these conditions because they seemed a reasonable facsimile of what might go down for a typical mash on a typical brew day. While there was no actual grist, and slightly less water than my usual BIAB mash, the times and temperatures would be pretty normal.
In Table 1 (above) and Chart 1 (below) you can see the results. Having run the experiment twice, I observed that on average the naked kettle lost 10 ºF (5.5 ºC) over an hour, while the single layer of Reflectix lost only 5.5 ºF (3 ºC), and the double layer lost 4.5 ºF (2.5 ºC).
In other words: It works! Still not quite as well as I’d hoped, but certainly better than nothing at all.
Conclusion
The Reflectix insulation is an inexpensive way to make a serviceable insulated jacket for your kettle. For BIAB brewers who place a premium on simplicity, it doesn’t get much better than this. You can make yourself a jacket in just a few minutes, and from there on out you can reasonably expect to hold your mash temperature within 3–5 ºF (1.6–2.8 ºC) over the course of an hour.
Even though I started off using the Reflectix with a blind faith as to its usefulness, the experiment (along with the other data I’ve collected over the past couple months) has convinced me that it’s a worthwhile part of my brewing process.
(P.S. If anyone is wondering what happened to the 5 gallons (19 L) of water from the experiment, fear not! It was not wasted, I used it in a batch of mead I made that afternoon.)
