Maximize Your Mash: Understanding Impact of Equipment & Temperature
There is an old saying that brewers make wort but yeast make beer. It is hard to argue against that fact, but the wort we feed the yeast will determine the final qualities in the beer. For example, the sugars available in the wort and its fermentability are critical parameters in determining how the beer will be perceived in the mouthfeel. Targeting the appropriate enzyme groups during mashing and providing the ideal conditions for its activity, the brewer can then have much of the final say in what the beer will be like.
A big factor in determining wort fermentability is the mash temperature(s) used and the length of time at that (those) temperature(s). In general, more fermentable worts are produced at lower temperatures where beta amylase is more active, and less fermentable worts are produced at higher temperatures where alpha amylase is more active. These enzymes are active in a wide range of temperatures but they do have an optimal narrower range. The optimal temperature for these enzymes is not a constant and absolute value and this is reflected in Table 1 (above), where different optimal temperatures are quoted from different sources. The optimal enzyme temperature varies according to how the enzymes are treated in the process, and that is the basic topic of the story.
Beta/Alpha Amylase Optimal Temperature and Colloidal Nature of the Mash
To better understand the conditions that favor the action for beta and alpha amylase, it helps to consider the ideal conditions for these enzymes when working on pure starch solutions, compared to ideal conditions when working in a mash. The ideal temperature range for alpha and beta amylase is much lower when enzymes are working on pure starch as substrate in comparison to mash. Also, deactivation temperatures are 18 °F (10 °C) higher in mash compared to pure starch solutions. This raises two questions: Why do these enzymes have a lower deactivation temperature in pure starch versus mash? And why are these enzymes more effective at lower temperatures in pure starch versus mash?
In relation to higher deactivation temperature of
enzymes in mash versus pure starch, the answer can be rationalized in terms of mash thickness. It is well known that a thick mash provides better conditions for thermo-stable enzymes. For example, Figure 1 shows that beta amylase loses about 90% of its activity at 149 °F (65 °C) after 10 minutes at 1:5 ratio (kilograms of malt to liters of water), which decreases more slowly in concentrated mashes. In a 1:2-mash after 40 minutes of around 30% the activity of beta-amylase activity is still detected. This is the result of colloidal protection of the mash to enzymes.
Enzymes are large molecules with water soluble and water insoluble parts. Because these types of molecules are so long, they can fold into layers and adopt certain shapes. In the case of alpha and beta amylase enzymes, they adopt a spherical shape (they are classified as globular proteins). These spherically shaped enzymes are folded in such a way that the hydrophobic parts of the enzyme (water insoluble) remain deeper inside the sphere, leaving the water soluble parts of the enzyme on the surface of the sphere. Since only the surface of the sphere is in contact with water, enzymes remain water soluble/suspended even though they have a very large molecular weight. In the case of starch, these are even larger molecules. In both of these cases these can be visualized as very fine solid particles soluble (rather suspended) in water by chemical interaction. The resulting dispersion of fine solid particles is technically known as a colloid.
In brewing context, when malt is mixed with water, these fine particles disperse in water and remain in solution. Such solid matrix serves as a physical support system to stabilize the enzymes. In other words enzymes are most stable when bound to its substrate. Naturally, if more water is added into the mash, more dissolution and liquefaction of these particles occurs. It is more difficult for enzymes to retain a tridimensional shape in this kind of environment, and as a result enzyme activity is lost because its function depends on the integrity of its physical tridimensional shape.
The effect of colloidal protection seen in the mash is what allows enzymes to work at higher temperatures (preventing inactivation) but at the same time this colloidal protection can result in enzyme product inhibition (product accumulation in the enzyme surroundings), particularly when there is a lack of active diffusion mechanisms. Some of the reaction constants that describe the kinetics of enzymatic breakdown of starch by beta/alpha amylase were explained by Narziss.
The first step represented by K1 is the binding of enzyme with suitable substrate. This step is diffusion limited and is dependent on factors such as temperature, mash viscosity, mixing intensity and mash thickness. Once the enzyme has bound and worked on the substrate, there are relatively large molecules that can serve as a substrate once again. If the constant Kr of catalysis in comparison to the dissociation constant of the K-1 is very high, following the first degradation step further divisions may occur until the molecule is completely consumed. Only then connects the enzyme with a new substrate molecule. This mechanism is referred to as “chain attack.” If, however, the rate constant K-1 is much larger than Kr, the enzyme cleaves only one bond, separates from the degradation products and then connects with a new substrate molecule (“multichain attack”) going back to the original K1 binding step. In practical terms, K1 and K-1 constants are influenced by your process equipment (natural vs. forced convection during the mashing process) and this is explained in more detail below. The Kr constant is more dependent on mash pH because this has an effect on the ionizable groups of the enzymes. Having the correct mash pH will favor the repeated chain attack (Kr) mechanism vs the multi-chain attack (K-1).
Enzymes Behavior in Different Brewing Equipment Configurations
The three commonly used mashing systems — insulated single infusion, recirculated mash systems-heat ex-change recirculated mash systems (RIMS-HERMs) and mash mixers — all treat the mash and its enzymes in a different way, mainly as a consequence of the mechanism used for temperature control. How each system affects the performance of enzymes and how each system compares to each other will be discussed.
Insulated Single Infusion
The insulated single infusion mash tun is the most commonly used system in microbrewing environments. This is also what most of us are using (or have used) to make beer at home because of its simplicity of operation. Water is heated up to the desired temperature and malt is mixed in it. Once the malt has been mixed with hot water, no more mixing or heating occurs.
Because this type of mash is generally conducted thick (water to malt ratios lower than 3:1), there is a good deal of colloidal protection to the enzymes in the mash. This helps with the stability of enzymes to high temperatures. One drawback of the insulated single infusion mash is the lack of active diffusion mechanisms to promote the starch degradation process (forming new enzyme to substrate bonds, K1). Inducing the formation of enzyme-substrate complex is important, particularly in concentrated mashes because these have a natural tendency for product inhibition as a consequence of its high concentration (reference: Brewing Science and Practice, Chapter 4.3.7).
In comparison to well-mixed systems, such as mechanically mixed mash or RIMS, a slightly higher mash temperature may be used to promote better diffusion and interactions between enzyme and substrate. This is possible because of the high colloidal protection in the system, which allows the enzymes to function at higher temperatures for a longer time.
Re-Circulated Infusion Mash (RIMS/HERMS)
The recirculated infusion mash system is a very popular configuration in homebrewing. In this type of system, the mash and lautering process is done in the same container usually equipped with a false bottom. Wort is continuously removed from below the false bottom and pump-recirculated/heated in-line on its way back to the top of the mash tun. One RIMS configuration that uses a water immersed coil as the heat source for heating up the wort is more commonly known as HERMS (heat exchanged recirculated mash system). The best RIMS systems spread the wort uniformly on top of the mash tun and little channeling occurs during the recirculation process (low flow rates for recirculation are necessary here). If this is done effectively, better results will be obtained in terms of mash efficiency in comparison to the single infusion process because there is a forced convectionprocess to promote new enzyme to substrate bindings (K1).
One disadvantage of recirculated infusion mash systems is that the continuously filtering action of recirculation through the grain bed removes much of the natural colloidal protection of the mash, making the enzymes more vulnerable to the effects of high temperature when passing through the heating element. To diminish this problem, a large heating surface area should be used with a low temperature differential between the mash temperature and the heat source. This temperature differential is critical when pumping the wort through a long heating loop because by the time the wort returns to the mash, the temperature of the wort will be equal to the temperature of the heat source. It is worth mentioning that enzymes do have a large range of working temperatures, and while enzymes are capable of working even at much lower temperatures than the optimal temperature, the case is very different once the temperature gets to be higher than optimal. As seen in this graph, after crossing the optimal temperature on the high side, irreversible inactivation is likely to happen very quickly.
In comparison to insulated single infusion systems, the mash temperature should be slightly lower temperature to compensate for mixing effects as more enzyme activity may be obtained at the same temperature due to improved diffusion.
Mechanically Stirred-Heated Mash (Mash Mixers)
Mash mixers are not as commonly used as single infusions or RIMS systems in homebrewing, but they are used. A mash mixer is a dedicated mashing vessel (lautering is done in a separate vessel) that consists of a mechanical mixer and heater. The mixer and heater work together as a system of temperature control. In large scale systems the heating is applied by means of steam jacket, but for homebrew-size mash mixers, the heating may be applied by direct fire, indirect heat with internal hot water coils or externally placed electric heaters.
In mash mixing systems where the mash is continually agitated, a similar degree of colloidal protection of insulated single infusion systems is expected. This is because wort is never separated from the mash as in re-circulated systems for heating up in temperature ramps. A technical advantage of a mechanically mixed mash systems over non-agitated single infusions is that the product inhibition effect is diminished because of the active mixing action promoting enzyme to substrate binding (K1 reaction). One aspect to point out is that mechanically mixed mashes are often conducted more diluted in water compared to single infusion insulated systems, often 3.5:1 to 4.5:1 water to malt ratios. While it is true that the thermal stability of enzymes diminishes at higher water/malt ratios, in mash mixed systems the starch breakdown is normally conducted in short steps targeting the optimal temperature of the desired enzyme. This allows the full conversion of starch by the given enzyme in a short amount of time before the enzyme can be inactivated. The table below shows a step mash schedule where a separate beta and alpha amylase are conducted.
In comparison to insulated single infusion and recirculated infusion systems, the temperature should be slightly lower in mash mixers to account for the effects of mixing. Well mixed systems are not diffusion limited and comparable effects may be achieved at lower temperatures. In comparison to recirculated infusions, the enzymes working in mash mixed systems have a better degree of colloidal protection.
In summary, the three brewing configurations discussed are perfectly suitable for making good beer. Each system works differently, therefore there will be differences in the optimal temperatures for the targeted group of enzymes. For example, within the broad range of most accepted temperatures for beta amylase, say 140 to 149 °F (60 to 65 °C), it is possible that in one brewing system beta amylase will peak in activity at 144 °F (62 °C) while in others the optimal can be slightly lower or higher. This is a matter of knowing how your particular system responds, and why brewing research will go on forever!
