Walter Diaz, Tucson, Arizona
A. Excellent question, Walter, and very nice empirical data related to this topic. I don't think there is any question that mash mixers have a very real effect on extract yield and this is certainly one of the reasons they are used. When writing about mashing I often combine the topic of multi-temperature mashing together with the tool of choice for the process, the mash mixer, and really take the tool for granted in these mash discussions. So I will spend a little time focusing on the humble mash mixer.
The types of mash mixers used by commercial brewers have three main features. The first is the grist hydrator, which is a device designed to blend water and grist as the two streams flow into the top of the mash mixer. Most grist hydrators are designed in such a way to combine the two streams without the use of any motors or internal components that may clog when used and the desired result is uniformly hydrated grist flowing freely into the mash mixer. If grist is simply dumped into a mash mixer while water is being pumped in from a separate line, the result is large clumps of grist that are not fully hydrated. These clumps never fully break apart during mashing and you end up with a decrease in yield. For this reason, grist hydrators are really important features of well-designed mash mixers.
The second and third key features of the modern mash mixer are tied at the hip, so I will discuss them together; these features are the mixer and the heating jacket. The primary purpose of the mixer is to move the mash around in order to provide uniform heat transfer from the steam jacket to the mash. If the mixer is run too slowly, or simply turned off for experimental purposes, the mash touching the steam jackets will become very hot and begin to boil, but the mash a few inches into the center is slow to react to the heat because mash is thick and does not develop convection currents like pots of liquids that do not contain solids. The home cook knows to gently stir a pot of chili when placed on high heat to avoid scorching the bottom of the pan and the food adjacent to the heat source, and this is really how the mixer is used in a mash mixer.
A mixer is really a type of pump when one considers how the mixer affects the fluid in the container being mixed. Mash mixers are designed to pump the mash downward into the bottom of the mixer. When this happens, the mash flows across the surface of the bottom "head" or dish of the mash mixer and up the sides. Since the heating surfaces are located on the bottom head and the shell of the mash mixer, this pumping motion greatly improves uniform heating of the entire volume of mash. Almost all modern mash mixers use low-shear mixer impellers that run at a relatively slow speed and do not excessively damage husk pieces during the course of mashing. This feature improves the performance of the lauter tun and is considered an extremely important design element of the modern mash mixer. Some older mash mixer designs used mixers that caused more shear damage than modern designs and, due to their less than ideal shape, were often equipped with baffles to help keep the mash homogeneous.
The steam jackets are used for heating, and most mash mixers are nearly covered with heating surface when in use. Homebrewers very, very rarely have steam-heated equipment and instead use electric or gas flame heaters for mash mixers. The important thing to take away from steam-heated designs is the ability to turn off the heat with very minimal thermal lag. If you are heating mash on a kitchen stove and turn the heat off, you know that the heating element does not cool instantly and will continue heating the mash. Even with steam- or gas-heated mash mixers there is a time delay between turning the heat off and the cessation of heating as measured by changes of temperature within the mash. These are forms of thermal lag and experience will tell you how much lag to expect in your system. In order to control the process, know your lag and simply shut the heat supply off before hitting your set point.
So that is a basic description of the tool known as the mash mixer. One of the nice things that accompany grist hydration and mash mixing is improved extract yield over infusion mash systems. The reason for the improvement in yield is exactly as you suspect; the continuous or intermittent mixing, depending on how the mixer is used, improves starch dissolution and this has a direct effect on extract yield.
I think many homebrewers assume that commercial brewers use mash mixers only when they want to brew beers that benefit from multi-temperature mashing. But the fact is that the mash mixer and lauter tun brewhouse configuration has a few very real advantages over the simple infusion mash method that indeed works so well for smaller brewers. Mash mixers are easy to operate, they can consistently be used to produce uniform mashes, they can be used for single or multi-temperature mashes, they can be used to mash-off before transferring to the lauter tun, and they are easy to clean.
Lauter tuns are easier to fill than infusion mash tuns because the mash thins dramatically during mashing, they are used in conjunction with mash mixers to achieve very high extract yield (usually in excess of 92% of laboratory or hypothetical yield), and quickly and efficiently discharge the spent grains after sparging. This is why craft brewers began migrating away from infusion mash tuns as breweries grew in size.
At Springfield Brewing Company we have a 3-vessel brewhouse consisting of a combination mash mixer/brew kettle, lauter tun and whirlpool. We use our mash mixer for a variety of mash types, ranging from long, multi-temperature mashes with the occasional inclusion of rice or corn, to short, single-temperature mashes followed by mash-off at 168 °F (76 °C). Our mashes are pumped to our lauter tun for wort collection and our typical extract yield for brews up to about 15 °Plato (1.061 SG) is right at 94% of laboratory yield. We monitor our wort gravity during wort collection and terminate wort collection when we hit 2 °Plato (1.008 SG).
Q. I batch sparge and cannot seem to find an answer to a question i have had for some time. When batch sparging, is it the sparge water that should be at my mash out temperature, or is it the grain bed that needs to be at my mash out temperature? It seems to me it would be the grain bed, because my friends that directfire their mash tun will bring the grain bed to the mash out temperature. But my batch sparge friends tell me it is only the sparge water that you add that should be at the mash out temperature, which would not bring the grain bed up to the mash out temperature.
Fort Collins, Colorado
A. This question is a bit more about semantics than any real issues with sparge temperature, in my view of things. Bear with me while I explain how commercial brewers normally mash out and sparge. Most commercial brewers use stirred mash mixers for mashing and raise the mash temperature to about 168 °F (76 °C) before pumping the mash to the lauter tun. When sparging ensues, the water temperature is normally controlled to about 168 °F (76 °C). These procedures vary among breweries, but in general this is how things are done. The practical reason for controlling sparge water temperature instead of monitoring the grain bed temperature is because measuring and controlling water temperature is easy and reliable, whereas measuring and attempting to change the grain bed temperature by changing the sparge water temperature is neither easy nor reliable. Lauter tuns have raking machines that cut the grain bed and rarely have temperature probes installed to monitor grain temperature because there really is little use for measuring the grain bed temperature during this relatively short process.
OK, let's move into the homebrewing realm and discuss infusion mashing for a moment. In the infusion mash tun there is no practical way to stir the mash and increase the mash temperature as with a mash mixer. This is why the name "infusion mashing" is often more completely described as "single-temperature, infusion mashing." Brewers who use infusion mashing often times use the same basic brewing rules as those who use stirred mashing and sparge with 168 °F (76 °C) water because they do not want to run the risk of extracting tannins from the malt husk with hotter water. The truth is that hotter sparge water can be used since it is the temperature of the whole that is important when it comes to solubility.
When you batch sparge you don't control sparge flow rate like the typical continuous sparging set-up, but the temperature control methods are the same; sparge water is heated in a single hot water tank to the desired temperature or very hot water and ambient water are blended in-line as the water flows into the sparge line. If you are an infusion masher (no mash off used) and would like to add a few levels of complexity to your rig, you could measure the wort temperature as it exits your mash tun and use hotter water to bring the wort temperature up to 168 °F (76 °C). After this temperature is hit, you would then want to finish the sparge with 168 °F (76 °C) sparge water. As I write this, the process engineer in me cringes since this is a veritable control logic train wreck for a reason I am not sure the average small commercial brewer or homebrewer is likely to not be able to justify from an economic or flavor perspective. I hope this answer has given you some information to fine-tune your sparging technique.