Mash Stirring
Q: I was doing a little research the other day and came across the Sabco RIMS-WIZARD. Their website claims that stirring of the mash is not recommended. What is your opinion on stirring of the mash? Is there much information available?
— Frank Uhi • Brockay, Pennsylvania
A: There is indeed much information about mash stirring and the use of agitated mash mixers is the norm in modern commercial breweries. The primary reason for stirring the mash is to provide uniformity when heating the mash. Brewers who employ step mashing, sometimes referred to as upward infusion mashing, double mashing and decoction mashing all use mash mixers. I think that the history of brewing clearly shows that mash mixers were first developed to deal with the challenge of uniform heating.
A side benefit to stirring the mash is improved yield. In large mash mixers another consequence to mixing can be shear damage from aggressive mixer designs and/or the use of baffles in mash mixers. Companies that design and build equipment for breweries have addressed the problem of shear damage by using low shear mash agitators designed to pump the mash down to the center of the mash mixer bottom. The mash then flows across the bottom and up the sides; since the mash mixer bottom and side walls are typically steam heated this flow pattern is ideal for heat transfer. Although many mixer designs are touted by equipment manufacturers, they all work on similar design premises.
When mash mixers are used during mashing there is always a separate wort separation device, be it a lauter tun, mash filter or the now obsolete Strainmaster once used in many of the Anheuser-Busch breweries. All of the devices are designed to separate clear wort from the grain bed. A common feature of all of these devices is that the mash is not stirred during wort separation. Despite the appearance of a lauter tun raking machine, it does not stir the mash when properly designed and used, rather it gently cuts and lifts the grain bed while very, very slowly rotating.
The traditional infusion mash system is totally different than the mashing systems I just mentioned. In an infusion mash tun the malt and water are mixed during mash in, the mash is distributed by the brewer using a mash paddle (or mechanical device in larger mash tuns) and the mash is held without heating during enzymatic conversion. After conversion is complete, the false bottom of the mash tun allows wort separation to occur in the same vessel. Infusion mash beds are not disturbed during the mash rest and there is no raking machine in the traditional mash tun.
The RIMS (Recirculated Infusion Mash System) method of mashing is based on infusion mashing in that the mash is not stirred during mashing and that the mash vessel is also used during wort separation. The thing that distinguishes RIMS from traditional infusion mashing is mash heating, and with RIMS mashing the heating is made possible by the use of a wort recirculation pump and external wort heater. My guess is that mash stirring is not recommended because excessive stirring could lead to problems with wort separation after the mash is complete.
In the 5-gallon (19-L) pilot brewery at UC-Davis where my fellow graduate students and I brewed as much as we possibly could, we had a “lauter tun” located below the mash mixer. When doing stirred mashes, the mash was gravity transferred from the mixer to the “lauter tun” (no raking machine). When we did infusion mashes we would simply mash into the “lauter tun” and contrary to what is often written about infusion mashes we would periodically give the mash a gentle stir and we never had any problems with a stuck bed or wort turbidity issues that extended beyond the recirculation of wort prior to wort collection.
For the last 13 years I have formulated numerous styles of ales and lagers at Springfield Brewing Company and all of these beers have been brewed using a mash mixer and a lauter tun. So stirred mashing is what I know best. What I can attest to is very good extract yield, excellent repeatability and freedom to brew just about anything we can dream up.
