By Jim Busch (Brewing Techniques)
In this installment of “Stepping Up,” we investigate the process of lautering and review some of the common situations that can cause lautering problems. Lautering is a fairly simple process, but also a very important one. No matter how well a brewer’s grains are mashed, if the mash is not lautered correctly the extract will not be realized, leading to low original gravities and lower alcohol levels. Poor lautering results, at the very least, in wasted money for the brewhouse and, at the worst, negatively affects the beer’s flavor profile.
In its simplest form, lautering is merely the controlled rinsing or washing of the sugars from the grains. At the end of the process, the brewer has a full kettle of sweet wort and a lauter tun full of spent grains. The spent grains go to the compost pile, and the sweet wort is boiled with hops to make bitter wort for subsequent fermentation.
The process of washing the grains involves careful regulation of temperature and pH. Temperature is important because sugars are more soluble at higher rather than at lower temperatures, which means greater extraction efficiency. The ideal lauter temperature is between 168 °F and 176 °F (76–80 °C).
The pH level is important because most water supplies are alkaline; the more you lauter, the more the pH of the sweet wort will rise toward alkalinity. Typically, mash pH is in the 5.2–5.7 range before lautering. As you add water to the mash, the pH gradually rises.
It is important that the pH not rise too much; a level of around 6.0 is usually the highest acceptable. At higher pH levels, tannins from the grain husks can be leached into the sweet wort, leading to unpleasant astringency in the finished beer. To prevent this, some brewers adjust the pH of their sparge water to between 5.7 and 6.4 by adding lactic or phosphoric acid. The mash is an effective buffer system, though, resisting changes to the pH and actively working to keep the pH down in the 5.0 range. At the start of lautering the mash is a strong buffer, but as the sparge water dilutes it the mash’s buffering ability decreases and rapid pH changes can occur.
Lautering a typical homebrew batch of 10–15 gal usually lasts between 60 and 90 min. Lautering for less than 1 h is quite rare and may result in lower extract rates.
Some brewers lauter in a lauter tun separate from the mash tun; some use a combined mash-lauter tun. In the British system of brewing with highly modified malts and a single infusion mash, for example, the mash and lauter tuns are one vessel. Alternatively, step or decoction mashing is usually performed separate from the lauter tun, because these methods of mashing often require the addition of heat and stirring of the mash.
If you use a mash tun separate from the lauter tun, the first step in lautering is the physical transfer of the mash. When using a separate lauter tun, it is important to cover the false bottom with preheated water. This water is called foundation water and provides a kind of support that prevents the initial force of mash transfer from clogging the false bottom. The foundation water also helps to preheat the lauter tun, which aids in maintaining the final mash temperature.
Once the mash is transferred, lautering begins with a short period of recirculating the turbid runoff. The length of the recirculation period varies as a function of tun design, malt choice, and mashing programs. The goal of recirculation is to clarify the runoff, returning the first, cloudy runnings and thereby trapping some of the large particulate matter in the mash filter bed created by the grain husks that settle on top of the false bottom. In general, the clearer the runoff the better, but very clear runoff is usually neither obtainable nor completely desirable. In most home brewers’ tuns, the recirculation period lasts 10–20 min. In many commercial tuns it takes longer.
When recirculation is complete, the sweet wort is collected and sent on to the brew kettle. It is important to carefully monitor the rate of outflow from the tun; a slow runoff will help maximize extract efficiency. If the runoff is too rapid, it can lead to compaction or channeling of the grains, causing stuck sparges. Most brewers aim to keep the fluid level in the tun above the top of the grain bed to avoid a poor runoff.
As the wort runs off, add sparge water to keep the fluid level above the grains. This can be accomplished by using a ladle, a sprinkler device as in the Phil’s Lauter Tun, or a simple tube to carry the water into the tun. Whichever method you use, be sure to keep the water evenly dispersed across the grain bed. It is also worth noting that if you want to sparge with 170 °F (77 °C) water, you will need to measure the water temperature as it enters the tun. As a result of temperature losses in the piping, the water could be as much as 10 °F (6 °C) lower than the temperature measured in the hot liquor tank (sparge reservoir).
Lautering continues until the required volume of wort is obtained or until the specific gravity of the last runnings falls to 1.008. Although this is a good rule of thumb, another way of monitoring the runoff is by checking the pH level, thereby also ensuring that it doesn’t rise too high. If the pH is allowed to rise too high, then beneficial kettle reactions will be impaired and fermentation can be abnormal. High pH will also leach astringent tannins from the grain husks.
Some brewers like to knife the grain bed during lautering. Knifing the bed sometimes helps to avoid channeling and can result in higher extract. It can also be used to help a slow, semistuck lauter. Using the handle of a long stainless steel spoon or a long, broad knife, cut the grains from the top to within a few inches of the false bottom, but never reaching the false bottom. The knife can be dragged across the grains from one end of the tun to the other, like cutting a pie. In commercial tuns, this is called “running the rakes” and can be used to help suspend the grain bed. It is also used to aid the removal of spent grains.
Although relatively rare, most brewers have the misfortune of at least one stuck runoff. Stuck runoffs occur when the rate of outflow from the runoff is slowed to little or none. When this occurs, the first option to consider is knifing the bed. Be sure to knife deep into the bed, but try not to disturb the very bottom filter bed. If this fails to resume outflow, try underletting the bed with sparge water. If the hot liquor tank is high enough above the lauter tun, connect the outlet of the tank to the outlet of the lauter tun. Open the valve on the sparge reservoir first, then open the lauter tun valve. If no water flows, knife the grains to loosen the bed. If it is still stuck, stir the very bottom of the grain bed, allowing the underletting water to clear the blockage. Disconnect the sparge tube and recirculate the now turbid runoff, being careful to avoid a rapid outflow, which could result in another stuck runoff.
What causes stuck runoffs? Any one of a number of problems may be the source, but the most common culprits are overly fine malt crush, a compacted grain bed from too fast a runoff, poor mashing technique, cool grain-bed temperatures, and extremely high percentages (>70%) of wheat or other glutenous adjuncts. If the grains are overly crushed, the husks that are required to form a filter bed are too damaged to accomplish the task. A fast runoff will lead to grain bed compaction and could possibly force the filter bed to clog the false bottom. Poor mashing technique could leave too many gums and glutenous substances in the mash, thus increasing wort viscosity. Temperature is important, because the wort sugars are easier to remove when temperatures are high.
When brewing very strong beers like barley wines or Scottish strong ales, many brewers typically stop the runoff from the lauter tun before the final 1.008 specific gravity is reached. Often, the runoff specific gravity is in the 1.025–1.040 range when the runoff is stopped. If the grains are discarded at this point, a considerable amount of extract is wasted. To recover this extract potential, continue the runoff but divert it into a separate brew kettle (or holding tank for use when the kettle is free). This low-gravity wort can be boiled separately to produce a small beer.
In the United Kingdom, small beers are typically in the 1.032–1.042 range, falling squarely within the bitters category, so the beers are often hopped with traditional UK hops such as Goldings. When brewing small beers, monitor the kettle gravity to determine the proper boil time required to yield the correct extract. Often, a brewer would boil a regular batch for 60–90 min, but a small beer may need 2–3 h to reach the desired gravity. If a more robust beer is desired from the small beer, then crushed dark malts can be added directly to the lauter tun. Chocolate and caramel malts or roasted barley are often used.
If performed slowly and carefully, lautering produces the highest extract efficiency, resulting in higher original gravities and alcohol levels. Lautering is a simple process of regulating temperature and pH, recirculating to clarify the runoff, and monitoring the runoff from the tun to the brew kettle to avoid compaction of the grains and stuck sparges. Each of these steps requires thorough attention, but once lautering is mastered your overall mashing techniques — and your beer— will improve.
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