For thousands of years, the fermentation of cereal wort has challenged our ability to explain, predict and control the behaviour of yeast. Brewing has been described as an art; however, it has often been responsible for driving forward scientific theory and techniques. One of these techniques is the use of mathematical models to describe and predict fermentation behaviour. The advantages and disadvantages of modelling techniques (simple and complex) are discussed, as are models commonly used by industry. As fermentation is affected by many parameters, an overview of how some of these affect this process is discussed. Finally, applications and advanced brewing techniques (such as high-gravity brewing) are discussed.

The phenomenon of premature yeast flocculation (PYF) is suspected to be caused (at least in part) due to fungal infection of barley. This study reports on an ongoing investigation that has identified a link between fungal pathogens and PYF behavior. Two varieties of barley, AC Metcalfe and CDC Bold, were exposed to each of three common barley fungal pathogens (Pyrenophora teres, Cochliobolus sativus, or Fusarium graminearum) and evaluated for PYF behavior during fermentation. Barley was infected in the field between flowering and grain maturation. Each sample was micro-malted, mashed, and fermented using a moderately flocculent yeast strain (SMA). Fermentations were performed using the ASBC "Miniature Fermentation" assay (ASBC Yeast-14) developed to detect PYF and assess fermentability or yeast strain performance. In order to detect evidence of PYF behavior, the absorbance at 600 mu of fermenting wort was used to assess yeast in suspension (turbidity). When infected with C. sativus and F. graminearum, the turbidity profile differed significantly (P < 0.01) between control and infected samples for both varieties of barley malt. The nature of the disparity was indicative of PYF behavior. Among malts that exhibited PYF, excess FAN was also observed. This is the first report demonstrating PYF behavior resulting from infection with these pathogens.

The amount of CO2 within a beer is a function of CO2 solubility, which in turn is affected by temperature, containing pressure, and beer composition. Historically, this variable was assessed through empirically derived pressure/temperature charts with the first appearing about 1939. Modern methods often involve empirical or semi-empirical formulas that yield close approximations to the aforementioned charts (at typical storage conditions). Other methods to determine CO2 solubility incorporate additional variables such as extract and alcohol content. Unfortunately, the origin of various pressure-temperature solubility charts contained in ASBC's Methods of Analysis or MBAA's Beer Packaging: A Manual for the Brewing and Beverage Industries, are largely unknown, as are the composition of the beers used to create these charts! This discrepancy results in potentially inaccurate CO2 values for differing beer compositions and is especially problematic when assessing modern methods that incorporate additional parameters. This paper attempts to contrast and compare modern and historical methods while considering the limited CO2 solubility reports in beer and sugar and ethanol solutions. In this paper, the accuracy of CO2 solubility charts and formulas are discussed while considering assumptions reported by the original authors. Finally, modern formulae are used with non-linear optimization techniques to generate the likely composition of the “standard beer” used to construct the original ASBC solubility chart. It appears that a “standard beer” of yesteryear is stronger than an average modern beer with an alcohol content of 4.22% (w/w) and a Real Extract of 5.78°P.

Malt barley breeders and maltsters often strive to improve the quality of their product by improving fermentability. Small-scale assays are often used to assess the fermentability of wort produced from malt under standardized mashing techniques. However, anecdotal reports suggest that these assays have poor correlation with industrial fermentations in addition to inconsistency between assays. There are several factors that are likely to contribute to this behavior such as pitching rate, mashing regime, fermentation temperature, barley modification, and batch size. This study aimed to isolate and examine the effect of fermentor size on wort fermentability through the use of miniature-scale (15 mL) assays fermented in parallel to industrial sized operations. These miniature fermentations were conducted at identical temperatures to their industrial scale counterparts and used oxygenated wort mashed and pitched by local craft breweries. Wort density was measured throughout the fermentations using a portable densitometer while the turbidity was assessed via spectrophotometer at 600 nm. It was found that fermentation vessel size had a significant effect on the apparent degree of fermentation; however, observed disparities were consistent between the assay and fermentor dimensions. For example, a difference in final density of 1.1 +/- 0.2 degrees P was observed between the final density of a 19.6 hL craft brewery and the miniature fermentation assay over three consecutive experiments. However, when the wort from an 8.5 hL brewpub was tested using this lab assay, no significant differences in final attenuation were found (P > 0.05). The shear generated through consumption of sugar and subsequent production of carbon dioxide was theoretically determined for each fermentation. A reduced shear generated within the shorter (miniature scale) fermentors likely influenced the yeast floc distributions and subsequent final density.

Understanding the relative importance of various sources of mercury within ecosystems and their subsequent impact on biota requires a thorough understanding of the biogeochemical cycling of mercury. An important component of the biogeochemical mercury cycle involves the exchange of gas-phase mercury between the atmosphere and various landscape surfaces. This study examines air–surface exchange (flux) of gaseous elemental mercury in selected undisturbed and anthropogenically impacted aquatic and terrestrial landscape settings. The objective of this study was to quantify air–surface mercury exchange rates in these contrasting landscape settings, to put constraints on these rates and provide insight into physical processes controlling mercury flux. Mean daily mercury flux was typically low over natural forest soils varying from −0.4 (net deposition) to 2.2 ng m −2 h −1 (net evasion). Minimum and maximum flux rates measured at these sites over the diurnal cycle ranged from a minimum of −1.3 to a maximum of 5.7 ng m −2 h −1 . Low flux rates from forest soils was partially due to poor light penetration through the forest canopy. Average daily mercury flux over undisturbed glacial till soil at an open field site with full sun exposure was also low (0.9 ng m −2 h −1 ) compared to the same soil mixed over a depth of 2 m (8.0 ng m −2 h −1 ). Mean daily mercury flux rates measured over pristine freshwater lake surfaces were also low (0.7–6.5 ng m −2 h −1 ), although the overall range in flux varied more widely (−0.3 to 44 ng m −2 h −1 ). Total mercury concentrations in marine water at a moderately polluted coastal harbour site (mean c. 0.8 ng l −1 ) and mean daily mercury flux rates over salt water (0.7 ng m −2 h −1 ) were similar to those measured over freshwater lakes. The highest daily average and diurnal range in mercury flux rates were measured at two abandoned gold mine tailings sites (130 and 237 ng m −2 h −1 ). The abandoned mine sites comprised tailings high in mercury content due to the past use of the mercury amalgamation process in gold extraction from the ore. Flux rates from tailings were two orders of magnitude higher than those observed over undisturbed native soils of similar parent material. Higher flux rates at the mine tailings sites were accompanied by ambient air concentrations 5–10 times background levels at 20 cm above the tailings. Mercury flux from vegetation has not been widely considered. A preliminary study of mercury flux from a white pine tree ( Pinus strobus ) indicated that actively growing trees might play a role in the atmospheric mercury cycle.