Brew In A Bag Best Practices

You’ve heard by now that Brew-In-A-Bag (BIAB) is an easy way to start all-grain brewing — and it’s true! But that doesn’t mean, however, that it doesn’t require some attention to detail. Most importantly, when doing a BIAB you need to be careful with heat. Here we will explore the best practices for maintaining your mash temperature during BIAB.

In the Beginning

I used to be the guy who chased exact temperature mashing when I homebrewed. But I wondered, does the final product benefit to any noticeable degree from being mashed at any constant temperature for the entirety of the mash? Does kettle mashing have any drawbacks compared to cooler mashing? Based on conversion facts what do homebrewers need to do to make good beer?

It is a proven fact that when mashing grain, 90% of the conversion from starch to sugar occurs within the first 45 minutes. The mash also insulates itself and is further insulated by the metal kettle. In any mash tun, because of thermal mass and heat transfer laws the mash resists sudden temperature fluctuations. (I use the word fluctuate because not only does the mash resist temperature decrease, it also resists increase.)

Basic Processes for BIAB

With the exception of the bag in BIAB brewing, and insulation reference, the conversion process is the same for every all-grain brewer. The strike water is heated to 159 ºF (70 °C) or so, the bag is inserted (if BIAB), grain is added, (12 to 18 pounds/5 to 8 kg) stirred, covered, and the kettle insulated. The temperature should be about 152 ºF (67 °C), which is in the “zone” for most recipes.

Conversion starts the very second the grain is added to the water. Most brewers don’t start their timers until after insulating the kettle, and for me that’s about 10 minutes. I set the timer for 60 minutes, which is really 70 total with that first ten minutes, and walk away, and I don’t open the lid until the timer goes off.

I didn’t always walk away from the mash, however. In the beginning, when I started using BIAB, I checked the temperature every fifteen minutes. That meant I took the insulation off the kettle, removed the lid, stirred for a minute or so, recorded the temperature using the sidewall kettle thermometer, and then covered it all up again — for another fifteen minutes. This isn’t unusual for BIAB brewers, actually, as they also open up the kettle to stir the mash to prevent hot and cold spots in the mash. Of course, every time I went through that process the temperature dropped a couple of degrees. I have a bimetal sidewall mounted thermometer in my aluminum kettle and it’s about 2 ºF (1.1 °C) low compared to my new digital thermometer. Every time I calibrate it, it’s still 2 ºF (1.1 °C) off one side or the other, so I’m thinking it’s my eyesight. I didn’t always have two thermometers to calibrate one to the other, so in my early days of brewing I’d look at the bimetal thermometer in the kettle and freak out that 2–3 ºF (1-2 °C) was lost. That meant my beer would suck, so I needed to get that temperature back to 152 ºF (67 °C) ASAP before conversion stopped! So the guessing game would begin. How long to apply heat to correct that drop? And at what temperature will the 3 inches (8 cm) of wort in the kettle need to be heated to raise the temperature of all the grain in the kettle back to my mash temperature? 10 ºF (5.5 °C), 15 ºF (8 °C), 20 ºF (11 °C)?

To prevent the bag from melting when I increased the heat, I’d hoist the bag a few inches off the bottom, fire up my 160,000 BTU KAB4, and watch the thermometer. It would rise very quickly, like 10-15 ºF (5 to 8 °C) in just two minutes. I’d assume that was good enough, shut off the burner, lower the bag, and stir like crazy.
That process resulted in confusion. According to the sidewall thermometer, the temperature of the wort would go up 10–15 ºF 5 to 8 °C), but after stirring, the mash temperature didn’t change or went over my target of 152 ºF (67 °C) — not good. I didn’t understand this, so I went to the Internet and found thermodynamics – From Wikipedia: “A thermodynamic operation is an artificial physical manipulation that changes the definition of a system or its surroundings. Usually it is a change of the permeability or some other feature of a wall of the system, that allows energy (as heat or work) or matter (mass) to be exchanged with the environment.
For example, the partition between two thermodynamic systems can be removed so as to produce a single system.”

Keys to Understanding

I’m not a scientist, but I don’t have to be in order to understand the inherent considerations of insulation — and in this case we’re talking about a blanket and bag of wet grain preventing changes in temperature. Also that fire + kettle + grain + water is not a single system.

The problem with trying to recover even 1 ºF (0.5 °C) with a kettle full of wet grain is that the mass of grain is nearly impermeable to the heat applied to it without risking burning the sugars in the wort. Short of starting over with a new set of calculations by draining the bag, heating the wort in the kettle and putting the bag back in with full consideration of the grain temperature etc., trying to correct the temperature mid-mash is a crap shoot.

To further illustrate this, try putting a ½ inch (1.27 cm) of water in any size pan and place it on a stove at full flame, and then do the same with a quart, and a gallon. You’ll see that the energy and time needed to boil that water changes with the volume of water. So when we consider that grain bills are inconsistent the complexity of determining the final temperature is nearly impossible. For the sake of consideration the typical propane flame burns at 3,630 ºF (2,000 °C) — that, my friends, will melt quite a lot of things, let alone your fabric brewing bag!

So when you apply heat to the boil kettle knowing there are only 3 to 6 inches (7 to 15 cm) of wort — or if you don’t lift the bag (zero inches of wort) the “excess” energy superheats that small volume of wort. We all know that sparging at 170 ºF (77 °C) slows down conversion and I’ll bet two shiny nickels that the temperature at the bottom of the kettle exceeds 170 ºF (77 °C), otherwise, how can we raise the temperature of the mass if the temperature is less than the mass? So every time we apply heat we slow down or kill a portion of the enzymes, likely burn or alter the sugars in that space, and ultimately detract from the very perfection we’re trying to achieve.

There are charts to figure this kind of stuff but the variables for all of us are too many. Why? Because with every brewer and every brew, the grain volume changes, along with water depth, strike temperature, ambient temperature, sugar concentration, and on and on.

We can’t calculate the temperature of the flame relative to the time it takes to burn the wort in every kettle and circumstance, but we know that sugar burns at 350 °F (177 °C) and so does the polyester material — unless there is sugar-free liquid surrounding it, and then it does not melt or burn. Have you ever seen the video of the styrofoam cup filled with water sitting in the coals of a campfire? It doesn’t melt.

What Can We Do?

Strike temperature relative to the grain bill, ambient temperature, grain temperature, and proper insulation can be known and used to control the initial and thus somewhat predictable final mash temperature. And that is the key to mashing at proper temperature. Almost every brewing calculator considers these factors when creating a recipe and process sheet. Another point worthy of consideration is the temperature conversion scale range of mashing. Enzymes do their converting of starches to sugars from as low as 95 ºF (35 °C) on up to 165 ºF (74 °C) with different types of sugars created in specific temperature ranges. Because of the sophisticated malting techniques we are now beneficiaries of, most grains available to homebrewers are modified to react well between 143 ºF (62 °C) and 163 ºF (73 °C) without rests at lower temperatures that would produce different additional sugars.

So depending on the mouthfeel the brewer is trying to achieve, style of beer, etc. most homebrewers focus their mash temperatures in that range with the majority of advice pointed at the 152 °F (67 °C) mark. A temperature of 152 °F (67 °C) actually overlaps the conversion range of short chain more fermentable sugars (130–152 °F/54–67 °C) and long chain less fermentable (152–158 °F/54–70 °C). Again, popular advice tells us that if we mash at 152 °F (67 °C) our beer will be “good” and will not be too dry or too heavy (sweet), and that advice is correct in my brew house.

Facts is Facts

So let’s say that you hit your strike temperature, mashed in, and hit the mash temperature as well, and then thirty minutes into the mash you check the thermometer and notice a 2 °F (1 °C) loss. Since you’re on target today and are not about to lose 2 ºF (1 °C) no matter what, you decide to burn your wort and fire up to get that 2 °F (1 °C) back. Was it worth it and what did you gain? No, and nothing.

The reality is as long as the mash temperature is in the range for the style of beer you’re after, everything is just fine. The range at the lower end is 152 to 130 °F (67 to 54 °C) with optimum temperature for Beta sugars produced at 143.6 °F (62 °C), and at the higher end 156 to 163 °F (69 to 73 °C) with optimum temperature for alpha sugars produced at 152.6 °F (67 °C). As stated above, the majority of conversion occurs in the first 45 minutes and at 30 minutes it is ~75% complete.

If you insulate your kettle or use a cooler, by the time you notice a temperature drop you’re fighting a war that’s 75% over and the damage caused by superheating the already converted wort is far greater than what’s to be gained by firing up that burner or adding another infusion of hot water.

Strike water temperature is just the beginning of the mash temperature. If your grain temperature is lower than assumed the mash temperature will drop, sometimes by 3 to 5 °F (1.6 to 3 °C) more than calculated, and that can change fermentability to some degree. In order to hit your mash temperature consistently you have to consider temperature fluctuations where you store your grain, or if you buy grain from the LHBS or otherwise, stick it with a thermometer before input to the software, or leave it for an hour or so where you know what the ambient temperature is.

Also, bear in mind that “hitting the numbers” starts at the beginning with mash temperature / conversion / fermentability and completes all the way to the end of the cycle. If you expected 1.007 and only got 1.012 that may be a result of too high a mash temperature which resulted in a portion of the wort being unfermentable.

Don’t Burn the Bag!

Finally, be mindful of overheating your brew bag. See the photo on this page of a brew bag that was burned in the kettle by turning the flame on with a bag full of grain. You can see that the burns are equal distance and look similar indicating the construction of the burner or false bottom that touched the bag. Sugar burns at 350 ºF (176 °C) and so does polyester — dead enzymes, dead bag.

Issue: May-June 2016