Mash Stirring

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.

Response by Ashton Lewis.