Malt Extracts: Cause for Cautionby Martin Lodahl
Republished from BrewingTechniques' July/August 1993.
Worts made from extracts often present fermentation problems. These problems are in large part caused by the low free amino nitrogen levels characteristic of these worts and may sometimes be due to an extract composition that is different from what the extract's labeling indicates.
A stuck fermentation is always a tiresome experience, and in a brewpub or microbrewery it can be an expensive one. Similarly problematic is an apparently finished beer with an unexpectedly high terminal gravity, unusually long lag times before the beginning of fermentation, or unexpectedly high diacetyl levels. Each of these problems can result from any number of causes, but if the wort is all-extract, the problem may be the extract itself.
The definitive study of this effect was published in a professional journal three years ago (1) and was discussed in a home brewer's publication shortly after that (2,3). In the study, researchers at the University of Saskatchewan used a combination of high performance liquid chromatography (HPLC) and fermentation studies to explore the relationship between extract composition and the fermentation characteristics of worts prepared in a standard fashion from these extracts. One finding was that extract-based worts contained a generally lower level of free amino nitrogen (FAN) than the all-malt "reference" wort that the researchers had obtained for comparison from a commercial brewery. Another finding was the disturbing presence of substantial amounts of glucose syrup, invert syrup/liquid sucrose, and high-fructose corn syrup in many of the extracts tested, even in some of those labeled "all-malt extract."
To the acute frustration of many brewers, the researchers did not identify the extracts tested. The Association of Brewers contacted the authors of the study for more information and published a letter from Professor Ingledew in which he said that they indeed had no plans to release the names of the extracts tested (3). He said that they couldn't be sure whether the adulteration was done by the manufacturers or by the distributors. He also said that their sample might not be representative, because they tested only 44 "lager" extracts and no "ale" extracts (their terms, apparently derived from product labeling). His lab had neither the time nor money to handle additional testing or possible legal action. He also asserted that the burden of following up on the problem rested with the brewing industry, through the marketplace. Professor Ingledew then closed with the following paragraph:
In spite of my comments above, I have complete confidence in the results obtained in my lab by my colleagues. There is no doubt that some manufacturers are profiting from the addition of lower cost corn sugars to malt extract.
These conclusions concern extracts supplied through the same channels as those used by small-scale brewers. To quote from the study:
Forty-one malt extracts (all of light lager type) were purchased from a local brewing supply store. These malt extracts were called beer kits, home brew kits, concentrated brewing worts, or malt extracts for home brewing. . . . In addition, one bulk malt extract sample from a malting company and two bulk malt extract samples from a local brewpub were obtained.
The researchers used Red Star lager yeast for all of the fermentation studies. The extracts and tmihe reference wort were diluted with sterile, distilled water to 12 degrees P, were saturated with air, pitched with 6 X 10-6 viable yeasts/mL, and were fermented at 14 degrees C with constant stirring.
VARYING FAN CONTENT
The first sign of real trouble was the observation that the time that extract-based brews required to drop from 12 degrees P to 6 degrees P varied from a low of 45 h to a high of 173 h, compared with the baseline of 51 h for the commercial wort. In addition to this significant variation, they also found a strong correlation between FAN levels and fermentation rate -- the slow-fermenting worts had low FAN content. That finding comes as no surprise, because brewing literature has long linked low FAN content with a variety of fermentation problems including slow or incomplete fermentation (4,5). Ingledew has published widely on the relationship of FAN to stuck and sluggish fermentation in high-gravity worts, and a fascinating new article by Fix (6) establishes a clear connection between low FAN levels and elevated diacetyl production. Some of the extract worts had dramatically lower FAN content (and correspondingly lower fermentation rates) than the reference all-malt wort; one wort's FAN content was as low as 80 mg/L compared with the reference wort's 220 mg/L. Because it appears that a wort FAN content must exceed 150 mg/L to avoid stuck or incomplete fermentation (7), many brewers preferring to keep their worts above 200 mg/L, it is reasonable to expect a troubled fermentation from a wort made solely from extracts such as those tested in this study. I find it interesting that at least one extract had a FAN content significantly higher than the reference all-malt wort and that the correlation between FAN and the attenuation rate remained significant.
Also interesting was the "utilized FAN" figure the researchers obtained by subtracting the FAN content remaining after fermentation from the original FAN content, the difference having presumably been metabolized by the yeast. This figure differed substantially between the reference wort and the extract worts (see Table I).
As the table suggests, FAN utilization and fermentation rate are related. Fix (6) has shown that wort composition can dramatically affect a yeast strain's amino acid uptake and that a yeast's response to the wort environment is strain-dependent. Although the results may have been somewhat different had another yeast been used, the average utilized FAN for the extract worts in this study was 32% compared with 81% for the reference wort. The authors of the paper, noting that brewer's yeast metabolize di- and tripeptides slowly and can use no larger peptides, suggested that it was possible that the worts used in the production of the extracts were incompletely modified or that the concentration process resulted in the degrading or binding of a significant fraction of the original FAN. For now, though, all that is clear is that the FAN content of extracts differs qualitatively as well as quantitatively from that of the reference all-malt wort. This appears to be an area ripe for further research.
The real bombshell of the Saskatchewan group's paper are the results of the HPLC analyses of carbohydrate profiles. The researchers divided the extracts into three groups according to the contents listed on the labels (see Table II). Group 2 and 3 extracts listed various supplements and adjuncts, and the analyses tracked pretty well with the labeling. This in itself does not guarantee the quality of these extracts, some of which had low FAN content and lots of nonmalt sugars. Group 1 extracts, however, "were labeled at the source as pure malt extracts." Of the 21 extracts in that group, a commendable 14 had carbohydrate profiles "similar to the standard all-malt wort," which placed them in class 1. From here I quote from the study:
While the implications of all that sink in, let me make it completely clear that the list of extracts involved in this test has never been published, and I don't have access to it. Please don't bombard BrewingTechniques with requests for it. We will probably never know what extracts were tested in the Saskatchewan study. Professor Ingledew said in a letter to the Association of Brewers, "We have identified a problem. Your pressure on the manufacturers or packagers will ensure that the situation is rectified" (3). To a degree this is true. Few of us, however, have HPLC equipment in our breweries, leaving us only one sure defense against adulterated extracts: not using extracts at all until the industry can demonstrate that the problem is solved. For many, however, this course is impractical or undesirable.
BREWING WITH EXTRACTS
Taste panel testing and contest results suggest that it is possible to make very good beer using malt extracts, but many of us have at some time had problem extract batches. The degree of variation this study identifies suggests that we may not always have been at fault. Following are some guidelines for using malt extracts:
THE QUEST FOR QUALITY
The last decade has seen a dramatic improvement in the materials available to small-scale brewers. Though we're no longer living on the margins of a production and distribution system geared solely to serve the largest commercial brewers, we still are at a comparative disadvantage in purchasing our materials. By becoming informed consumers, we can make better beer and send the message that high-quality materials offer a supplier the greatest competitive advantage. We have seen this happen in some brewing products already.
(1) J. Paik, N.H. Low, and W.M. Ingledew, "Malt Extract: Relationship of Chemical Composition to Fermentability," J. Am. Soc. Brew. Chem. 49 (1991).
(2) D. Fink, "Brew News," Zymurgy 13 (5), 15 (Winter 1990).
(3) D. Fink, "Brew News," Zymurgy 14 (2), 14 (Summer 1991).
(4) D.E. Briggs, J.S. Hough, R. Stevens, T.W. Young, Malting and Brewing Science (Chapman and Hall, London, 1981).
(5) G.J. Fix, Principles of Brewing Science (Brewers Publications, Boulder, Colorado, 1989).
(6) G.J. Fix, "Diacetyl: Formation, Reduction, and Control," BrewingTechniques 1 (2), 20-25 (1993).
(7) M. Meilgaard, "Wort Composition," in The Practical Brewer (Master Brewers Association of the Americas, Madison, Wisconsin, 1977).
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