Mash Uniformity: Single-vessel temperature stability
Single-vessel, “brew-in-a-bag” brewing had humble beginnings as a very simple and budget-friendly method on the fringes of the hobby. As it became more popular, system builders began innovating by adding electric heat, digital temperature control, and recirculation pumps, which aimed to match the precision of much larger and expensive 3-vessel systems.
After brewing on various systems in this category and data logging temperatures at different areas of the mash, I discovered that a simple and relatively inexpensive modification can be made to maximize temperature stability and uniformity. This is not to suggest good beer can’t be made with primitive gear, rather that if you already have a system like this, or are building one, higher levels of stability are possible and may be warranted if the following benefits are appealing to you:
- Temperature uniformity throughout the entire mash volume allows for batch repeatability and accurate communication of recipes between brewers because you know what the mash temperature was instead of a recording of a single spot in the mash (where the probe is installed).
- Heat is more quickly distributed when ramping for step mashes, again allowing for faster and more precise arrival at target temperature across the entire mash.
- Heat is moved away from the heat source quickly to reduce the chance of scorching wort.
The drawing above illustrates heat movement in a single-vessel system. Heat is added at the bottom, whether by direct flame or electric element and exits primarily through the sides and top of the vessel.
Adding an insulation layer can reduce the heat loss, but it is seldom done because it detracts from the aesthetics of the kettle and needs to be removed when cleaning up.
A more common way to hold temperatures throughout the vessel is to pump the recently heated mash liquor from the bottom to the top of the grain bed. However, a delicate balance needs to be struck. If you pump too slowly, the top of the mash will always be significantly colder than the bottom. Pumping too quickly will overwhelm the flow rate that the mash and bag (or basket) can handle and an air pocket will form in the bottom right where the heat is being applied. The result is scorching or dry firing the element. It is often difficult to dial in the perfect flow rate because we are trying to restrict a 7-gallon-per-minute (26.5-L-per-minute) pump down to a mere 5–10% flow.
The last unique situation to consider applies to systems that contain the mash within a solid-sided basket where some amount of liquid surrounds it. This surrounding liquid is always the coldest area and never gets replenished with typical recirculation to the top of the basket. Temperature differentials in a single-vessel mash have been measured upwards of 8 °F (4 °C).
In summary, this particular evolution of a recirculating single-vessel brewing system has the most stable and uniform temperatures, as well as fastest step ramping that can be achieved at the homebrewing scale.
Tools and Materials
- Single-vessel or brew-in-a bag brew system
- Recirculating pump
- Whirlpool port with valve
- Recirculation arm
- Tee fitting (appropriately sized to pump and system)
- Valve (appropriately sized to pump and system)
- Quick connects (appropriately sized to pump and system)
