Q-&-A with the Troubleshooter
Dave Miller takes on...
  • Steeping vs. Mashing Efficiency
  • Controlling Esters in Scotch Ales
  • Calming Qualms about Chlorine Dioxide
  • Halting Fermentation at a Specific Gravity
  • Lagging Lager Attenuation

    Republished from BrewingTechniques' May/June 1997.

    Steeping vs. Mashing Efficiency

    Q: Noting that extract efficiency is lower when steeping specialty grains compared with that gained by mashing specialty grains, can I assume it is OK from a flavor/color/sugars standpoint to appropriately increase the amount of specialty grains that I intend to steep? Although this efficiency difference is not an issue for all-grain brewing, it does become important when converting all-grain recipes to extract-plus-specialty grain recipes.

    I would like to match as closely as possible the contributions of the specialty grains in the extract recipe to the contributions they would have provided in the all-grain version of the recipe. As an example, in the September/October 1996 issue of BrewingTechniques (1), John Palmer shows that his 120° L crystal malt contributes a typical 28 pts/lb/gal in a mash versus a typical 16 pts/lb/gal in a steep. By dividing 28 by 16, I get a ratio of 1.75 lb of mashed grains to 1 lb of steeped grains; in other words, I would have to use 1.75 times the amount of steeped grain to achieve the same contribution toward the specific gravity that I would get from 1 lb of mashed grains.

    A: You're right. Usually, steeping does not give you as much extract, color, or flavor from the same amount of a given specialty grain as does mashing. John Palmer's number gives you a reasonable starting point for a trial run, provided you are doing your steeps the same way he does. Home brewers, however, have a lot of different steeping methods from which to choose. In any case, remember that every brewery is different and that even if you try to follow his methods you may have to adjust your correction factor based on your experience.

    As a general guideline, at least three factors will influence the amount of color, flavor, and extract you get from specialty grain steeps: water temperature, steep time, and fineness of grind. Increasing any of these should increase the yield from your steep grains. There are practical limits, however. For example, I would not recommend a steep temperature higher than 168° F (76° C) for the same reasons I recommend holding sparge water temperatures to that value. Also, past a certain point -- 30 to 45 minutes, in most cases -- you won't get enough additional extract to justify the extra time you're taking. Grind is even more problematic. It is very difficult to separate the flourlike particles of a finely crushed grist unless you have the patience to pour your steep wort through a filter such as a coffee cone. It all comes down to a trade-off of time and effort for efficiency.

    Controlling Esters in Scotch Ales

    Q: In the Classic Beer Style Series #8 on Scotch ale (2), Greg Noonan suggests pitching large amounts of yeast to reduce ester production in Scotch ales. Can you explain this? Does this imply that ester production is mainly a product of the growth and respiration phase of the yeast life cycle? Would this also imply that oxygenation would be less important if large quantities of yeast are pitched? Before reading this text, it was my understanding that esters were more likely to be produced at warmer fermentation temperatures and in worts that were not oxygenated enough (oxygen drives the chemical reactions toward the acetic/ethanol pathway and away from the ester-producing chemical pathways).

    A: Basically, Greg is right, though I'm not sure I agree with his advice. As a rule, low pitching rates will yield higher levels of esters in finished beers. (For more details on this, see reference 3.) Other factors that affect ester production include pitching and fermentation temperatures (as you said), wort gravity and composition, and, of course, the yeast strain's inherent propensity for ester production.

    All other things being equal, higher pitching rates lead to less growth of yeast in the wort -- in other words, higher pitching rates provide a higher percentage of old yeast cells, which tend to be less adventurous about taking minor metabolic pathways like ester synthesis, preferring to stick to the main road, which is alcohol production. Old yeast cells also tend to be less vigorous about fermentation. This is why breweries that repeatedly repitch their yeast generally avoid high pitching rates -- the practice leads to a "graying" of the yeast population. You don't want sensible middle-aged yeast that go to bed at ten o'clock every night (in other words, yeast that get tired and stop fermenting when there is still sugar in the wort); you want a bunch of young, dissolute kids who will party until every last drop of sugar is gone. As Dr. Wen-Ping Hsiu put it, "Yeast are like people -- only the young can be strong!"

    For the sake of ensuring a complete fermentation, I think it is essential to aerate your wort fully, even if you choose to use a higher-than-normal pitching rate. If you are a micro- or pub brewer whose production yeast is prone to ester formation, then Greg Noonan's advice is good.

    The only thing I would add is, don't reuse the yeast from your batch(es) of Scotch ale. For home brewers, the simplest way to get the clean flavor profile of a typical Scotch ale is to use a yeast that is not prone to ester formation, such as Wyeast 1056 (American Ale). I have made some very clean Scotch ales with this yeast using my normal pitching rate, aeration method, and fermentation temperature.

    Calming Qualms about Chlorine Dioxide

    Q: BrewingTechniques' recent article on chlorine dioxide (4) leads me to question its use as a no-rinse sanitizer. It seems that, because chlorine dioxide is an oxygen donor, it would also oxidize the beer in the keg or tank. Any comment?

    A: Your concern is reasonable, but in fact chlorine dioxide does not work the way you seem to think. When activated, sodium chlorite will form chlorine dioxide gas, which is dissolved in the sanitizer solution (see the equations on pages 78 and 80 of the article for the details). Chlorine dioxide gas is a compound; it does not have the same properties as the elements from which it is made (oxygen and chlorine) any more than table salt has the same properties as the sodium and chlorine from which it is made.

    The way chlorine dioxide kills microbes is that it reacts chemically with certain amino acids that contain sulfur. The amino acids are important building blocks in the proteins that help to form cell walls. When these proteins are destroyed, the cell wall ruptures and the organism dies. In the chemical reaction, the chlorine dioxide gas takes on an electron from the amino acid and reverts back to a chlorite ion. The amino acid gives up an electron, and giving up an electron is what chemists call oxidation. Many common oxidation reactions do in fact involve molecular oxygen (that's how it got the name), but many do not. That is why articles that talk about oxidation reactions can be so confusing to lay persons like us -- especially if we are brewers who get jumpy at the thought of oxygen in our beer.

    Just because oxygen is not liberated during the sanitizing process, however, does not mean that chlorine dioxide is innocuous. Other nonoxygen oxidizing sanitizers, including sodium hypochlorite and iodophor, have been demonstrated to produce off-flavors when they come into contact with beer. The issue needs to be settled with a practical test.

    One major American brewery undertook such a test some time ago. They dosed beer with 100- and 200-ppm solutions of activated chlorine dioxide, at rates of 0.1% and 1% by volume. Note that these concentrations are far higher than the 40 ppm recommended for general no-rinse sanitizing; they wanted to know what would happen in a worst-case scenario; that is, suppose the doser fed way too much sanitizer into the water and the beer actually got out the door. How bad would the beer be? Note also that the 0.1% addition is a realistic maximum for cans or bottles sprayed with sanitizer and drained before filling. The results were that, at a rate of 0.1%, even 110-day beer dosed with 200-ppm chlorine dioxide could not be detected from control beers that were not dosed. The beers dosed with 1% showed a thinner body (probably due to protein degradation), but no oxidized, phenolic, or other off-flavors. The beers dosed were standard North American-style light lagers, and the evaluations were done by trained taste panels.

    This brewery is now using activated chlorine dioxide for container rinsing, filler sanitizing, and a continuous 5-ppm spray biowash on the fillers during operation. Since they adopted this program, baseline bacteria counts on their unpasteurized, aseptically packaged beers have been zero.

    Unfortunately, many large breweries these days feel compelled to treat the results of their research as proprietary information. I regret to say that this research has not yet been published, and so I am not at liberty to disclose the name of the brewery. I can say that similar research has been undertaken at another large brewery, with similar results; this company also has adopted chlorine dioxide for their packaging operations. My informant is Charles Talley of Five Star Affiliates, who worked closely with the brewery in conducting this research.

    I can assure you from my personal experience: I have been using chlorine dioxide to sanitize kegs and bright tanks for over a year, and have seen no ill effect on either the flavor or the shelf life of my beers. If you use the product as directed, I think you will be gratified by the results you get.

    Halting Fermentation at a Specific Gravity

    Q: Thanks for your feedback on "soured beer" and Guinness (5,6). My question of the day is: How do you stop fermentation at a specific gravity? The reason I ask is that the good people at Hale's Ales (Kirkland and Spokane, Washington) are helping me make a homebrew similar to their Moss Bay Extra. One of the brewers suggested I stop the fermentation at a gravity of 1.014 or 1.015 (3.57-3.83° P). They skim the yeast off the top and artificially carbonate their beer. If I were to stop this fermentation early, prime the beer, then bottle, would I create a bunch of time bombs in my basement, ready to explode?

    The recipe calls for 0.25 lb cara pils dextrin, 1.5 lb crystal 35° L, 1.5 lb crystal 140° L, 6 lb pale malt extract, 1.5 oz Centennial hops (7.8%) for 60 minutes and 1 oz for 3 minutes. According to my Suds report, I should start off with a gravity of 1.060 (14.67° P). Any comments would be appreciated!

    A: The best way I know of to stop an ale fermentation is to crash cool the beer; that is, chill it to 32° F (0° C) as quickly as possible. This method will stop most ale yeast in their tracks, and it usually works on lager yeast too, if you do it quickly enough. I suspect that's how the folks at Hale's do it. The only other practical method would be to physically remove the yeast by filtration or centrifugation. Fining to precipitate the yeast might work, but usually finings are not 100% effective.

    In any case, I don't think arresting the fermentation is a good idea if you intend to bottle the beer. To bottle condition it, you will have to reintroduce yeast. This will do two things. First, it will turn your bottles into time bombs, as you say. Second, the yeast will consume the residual sugars, thus diminishing the malty sweetness which is (I assume) the reason the Hale's brewers arrest their fermentation.

    To get a higher terminal gravity in your ale, the simplest tactic would be to use a less attenuating strain of ale yeast. Check "The Yeast Directory" in BrewingTechniques' 1996 Brewers' Market Guide (7) for likely candidates. Of course, changing yeasts will also change the flavor of your beer, so you won't be duplicating your model.

    If your heart is set on brewing this beer at home, using the same yeast that Hale's is using, you will have to invest in two soda kegs and a used refrigerator. Transfer the beer from the primary fermentor to the first keg when the gravity is down to about 1.020 (5.08° P). Monitor the attenuation closely. As soon as the gravity hits 1.015 (3.83° P), put the keg in the refrigerator and set the thermostat for maximum cold. Let the keg lie on its side if possible so that the yeast won't get pulled into the draw tube when you rack the beer again. After a few days in the cold, move the beer under counterpressure to the other keg. Carbonate it and serve it as draft beer.

    Nothing is foolproof, but even if by some dreadful chance the finished beer resumes its fermentation, the soda keg will take the pressure (soda kegs are rated to 130 psi). You'll be a lot safer than you would be with bottles.

    Lagging Lager Attenuation

    Q: I am having a continuing problem getting the attenuation I have come to expect with my lagers. I have had this problem ever since I started brewing five years ago. I have tried adjusting everything I can think of -- the pH of the mash and sparge water, and the mashing and fermentation temperatures. The last liquid yeast I tried should have had an attenuation of 73-77%, but instead came in at 58.3% -- this even though I used a 1-qt starter and fermented for two weeks at 55° F (13° C). This is pretty typical of what happens in my home brewery. I am at a loss as to what might be causing it.

    One thing I have noticed is that when I bottle I tend to get a lot of bubbles in the siphon tube, which causes my beer to foam in the bottle. I have determined that the bubbles are coming from the beer and not from a leaky siphon. Is this an indication of something I am overlooking? Is it possible it is still fermenting? It does taste sweet before I bottle it. Is it possible to do some sort of a controlled experiment to find out where the problem lies? I really want to lick this problem if I can.

    A: First, a question. I assume you are calculating apparent attenuation? This is what home brewers usually mean by attenuation, and that's what I assume the 73-77% refers to. It means that a 1.048 wort should attenuate to around 1.012 as measured by the hydrometer. If that's the way you're calculating it, then yes, you have a problem.

    The usual causes of inadequate attenuation are underpitching (insufficient number of yeast cells), low viability of the pitching yeast, and inadequate yeast growth in the wort. Underpitching with a liquid culture is very common. A 50-mL smack pack of lager yeast requires two stages of propagation at room temperature and frequent aeration of the starter cultures throughout propagation. This method should provide enough healthy yeast to pitch a 5-gallon batch.

    To ensure adequate yeast growth in the wort, aerate the holy tar out of it after pitching. Use a stone -- it's the only method that you can count on to achieve saturation. I remain convinced that 90% of all home brewing fermentation problems are caused by inattention to these basic procedures.

    Another potential problem with lager beer is thermal shock. Your wort should not be more than 18° F (10° C) colder than your yeast starter at pitching. Greater temperature differences can occur if you propagate in a warm room and pitch into very cold wort.

    Your question about gas bubbles is suggestive. How clear is your wort when you pitch it? Lately these pages have seen a lot of discussion about the desirability of clear wort -- especially in lager brewing (8,9). The current consensus among commercial brewers is that the reason clear wort sometimes leads to weak and incomplete fermentations is the under-appreciated phenomenon of CO2 toxicity. Cloudy wort holds lots of particulate matter in suspension; the particles provide nucleation sites for CO2 bubble formation and the CO2 is promptly purged from the fermentor as it is generated. Without nucleation sites, the gas dissolves in the wort and inhibits the yeast. The problem is worst with lager beers because the lower temperatures allow the CO2 to dissolve more readily. (For those who are interested, a good summary of this research is included in reference 10.) So if your wort is very clear, CO2 toxicity may be part of your problem.

    The best way to track down the cause of the problem is to try changing one thing at a time in your procedures. If you have been racking your wort off the cold trub before pitching, try eliminating this step. Review your brewing notes and see if they suggest a possible cause. Then change that and see if it works. If you propagate your yeast in only one stage, for example, try two stages (one cup, then one quart). Or if you haven't been aerating the starters during propagation, try swirling them around three or four times a day throughout propagation. Both these measures will give you a higher cell count at pitching.

    The basic fact is that when you make lagers, you have a lot less room for error than you have with ales. Because of the low temperatures, you never get as much yeast growth in the fermentor as you do with ales. Any mistakes you make will be magnified.


    John Palmer, "A Beginner's Guide to Using Grain in Extract Recipes," BrewingTechniques 4 (5), pp. 22-27 (September/October 1996).

    (2) Gregory J. Noonan, Scotch Ale, Classic Beer Style Series #8 (Brewers Publications, Boulder, Colorado, 1993).

    (3) Edelen et al., "Effects of Yeast Pitch Rates on Fermentation Performance and Beer Quality," Master Brewers Association of America Technical Quarterly 33 (1), pp. 30-32.

    (4) Dana Johnson, "Applications of Chlorine Dioxide -- A Postrinse Sanitizer that Won't Leave a Bad Taste in Your Mouth," BrewingTechniques 5 (2), pp. 76-81 (March/April 1997).

    (5) Dave Miller, "Sour Mashing," in Q&A with the Troubleshooter, BrewingTechniques 3 (5), pp. 42-43 (September/ October 1995).

    (6) Dave Miller, "The Secret to Guinness Stout," in Q&A with the Troubleshooter, BrewingTechniques 5 (2), pp. 32-33 (March/April 1997).

    (7) Deb Jolda, ed., "The Yeast Directory -- The Compleat Guide to Commercially Available Yeast Strains," in The 1996 Brewers' Market Guide (New Wine Press, Eugene, Oregon, 1996), pp. 40-59.

    (8) Gary Knull, Readers' Tech Notes, "Trouble with Trubless Fermentations," BrewingTechniques 4 (5), pp. 14-19, (September/October 1996).

    (9) Three readers responded to the article cited in reference 9 in the Readers' Tech Notes section of the January/February 1996 issue of BrewingTechniques 5 (1), pp. 16-l8.

    (10) O'Connor-Cox et al., "High Gravity Wort Clarity and Its Effect on Brewing Yeast Performance," Master Brewers Association of America Technical Quarterly 33 (1), pp. 20-29 (January 1996).

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