Direct Injection of Steam for Mash Temperature Control
by Kelly E. Jones (Brewing Techniques)
A simple, inexpensive, easily fabricated steam heat system can provide precise temperature control for mashing.
I first learned about using steam for mash temperature control from HomeBrew Digest, a mailing list on the internet. Looking back, I am surprised the idea didn’t occur to me earlier. I recall doing a pilot-scale experiment on the use of steam for temperature control as part of a laboratory course in my chemical engineering curriculum. During this group experiment, one of my assigned tasks was to control the temperature of a 500-gal tank of an aqueous solution by adjusting the flow of steam through a pipe that emptied directly into the tank under the surface level of the liquid. The steam condensed almost immediately upon contact with the cooler liquid, thus transferring its heat to the liquid. To think I could have been replaced by an inexpensive automatic controller!
Safety
Before I delve into the nuts and bolts of steam injection, I want to emphasize the need for safety. Steam has a heat content many times that of boiling water, even when the two are at the same temperature. This heat content makes steam not only more useful but also more dangerous. Upon contact with the skin, boiling water quickly loses heat and drops in temperature; steam, on the other hand, stays at 100 °C until all of its energy has been transferred to the skin, at which point the steam becomes still-scalding 100 °C water. Steam can thus cause burns much more severe than those caused by boiling water and should be treated with due respect.
Note, too, that steam is actually a nearly invisible gas — the “steam” we see rising from an open kettle is actually condensed water vapor. Thus, make sure your system has no hidden pinholes or leaks that can emit unseen streams of scalding steam.
Given these caveats, though, the system described in this article is fairly safe. No high pressures are involved; it takes only about 0.5 psi to discharge the steam into the mash. Should the steam discharge tube become clogged, the pressure in the steam generator should get no higher than 15 psi before the pressure regulator begins to do its thing.
Advantages of Using Steam
Injecting steam directly into the mash tun offers many advantages, especially for home brewers mashing in picnic coolers or other nonmetal mash tuns. One of the chief drawbacks of nonmetal mash tuns is the difficulty of doing any type of stepped-temperature mash. It is possible, of course, to achieve temperature steps by adding measured amounts of boiling or very hot water or by decoctions. Adding hot water, however, also has the (usually) undesired result of thinning the mash, sometimes unacceptably so, and decoctions can be extremely time consuming. Home brewers who use picnic coolers therefore usually perform single-step infusion mashes. Steam provides a method for adding heat to such mash tuns and enables you to dough in at protein-rest temperature, raise the temperature to mash temperatures, and finally raise the temperature to mash-out, all without significantly thinning the mash.
Steam offers advantages even to those who mash in electrically or gas-fired kettles. Steam greatly reduces the danger of carmelization and virtually eliminates the possibility of scorching the mash because the steam temperature stays in the vicinity of 100 °C (the low pressure steam used in this setup is only a few degrees higher than 100 °C). Although stirring is still necessary to achieve even heat distribution, a momentary lapse in stirring will not result in a blackened mess (and ruined mash).
Steam may offer several advantages for commercial brewers as well. For those mashing in unheated tuns, direct steam injection might be a low-cost method of adding heating capability to the tuns for stepped mashes. This might be especially economical for those breweries that already use steam as a source of heat for the kettle. Furthermore, direct injection of steam offers certain advantages over steam jacketed tuns. The heat transfer rate will be higher, because of the absence of an intervening wall between the steam and the mash. Also, because the steam is injected directly into the bulk of the mash rather than at the periphery, the heat distribution will tend to be more even and require less stirring.
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