Dry-Hop Creep Potential of Various Saccharomyces Yeast Species and Strains

Previous research has shown that hops contain enzymes able to hydrolyze unfermentable dextrins into fermentable sugars when added during the dry-hopping process. In the presence of live yeast, these additional fermentable sugars can lead to an over-attenuation of the beer; a phenomenon known as “hop creep”. This study attempts to analyze the effect of different Saccharomyces yeast species and strains on hop creep, with the intent to find an ability to mitigate the effects of dry-hop creep by using a specific yeast. Thirty different yeast species and strains were chosen from commercial and academic collections and propagated for pilot fermentations. Brews were performed at the Anheuser-Busch Research Brewery (1.8 hL, 10 °P, 20 IBU) at UC Davis and split to 40 L cylindroconical fermenters, with one fermenter in each yeast pair receiving 10 g/L Centennial hop pellets towards the end of fermentation. Standard analytical measurements were performed over the course of fermentation, with real degrees of fermentation (RDF) and extract measured on an Anton Paar alcolyzer. In order to preemptively determine the amount of hop creep to be experienced with each unknown fermentation, bench-top fermentations with 20 g/L dry-hops were performed concurrently and compared to the pilot scale fermentations. RDF was significantly higher (p < 0.01) on dry-hopped than non-dry-hopped fermentations beginning two days post dry-hopping to the end of fermentation, with the exceptions of SafAle™ BE-134, a S. cerevisiae var. diastaticus, and UCDFST 11-510, a S. mikatae. No apparent correlation between flocculation and increased RDF was shown in dry-hopped treatments. pH was significantly different between the dry-hopped and non-hopped fermentations (p < 0.05 one day post dry-hop, p < 0.01 for all subsequent days); this may have impacted on additional attenuation. No yeasts in this study indicated their use for mitigation of dry-hop creep, but this is a first look at beer fermentation for some of the chosen yeasts. The results also present a new perspective on how hop creep varies in fermentation.

Assessment of Corrosion in the Interface Casing - Cement and its Effect on the Leakage Potential

The cemented annulus behind casings and liners is a critical barrier element not only for oil and gas wells, but also for geothermal wells and underground CO2 storage. Corroded casing has been identified as one possible leakage pathway along wellbores. The presence of CO2 and H2O at the cement-casing interface promote and accelerate casing corrosion and cement carbonation. Two different sets of experimental studies were conducted and compared to understand different mechanisms of corrosion to reflect potential well conditions and their effects on leakage. The first study involved the analysis of a sandwich section, composed of 13 3/8-in and 9 5/8-in casing with wellbore cement in between recovered from the upper part of a well in the Valhall field in the North Sea. A slice of the recovered cross section was exposed to environmental corrosion for about thirty days at ambient conditions. Analytical measurements were undertaken to evaluate the porosity and corrosion states together with the influence of contaminants on the corrosion rate.The second study involved laboratory investigations on assemblies of steel plates and wellbore cement (API class G). The steel in each assembly is corroded with different mechanisms (environmental and electrochemical), producing different corrosion rates. Single-phase gas flow testing was carried out on the sample assemblies to investigate the effects of corrosion on the permeability of the corrosion product and consequently the leakage potential. Additional analytical measurements were used (SEM-EDS, XPS) to evaluate the porosity, chemical composition and oxidation states. For the sandwich slim cross section evaluated in the first study, results of chemical characterization using spectroscopic analysis (XRF, FTIR) and post processing using principal component analysis, show that the major components of corrosion are iron oxides, however the corrosion is highly correlated to the presence of BaSO4 (Barium sulphate).The results suggest that the presence of slurry contaminants, such as drilling mud and spacers, may have an important influence in the oxidation rate acceleration. The gas flow tests from the second study indicate that corroded casing can have a significant effective permeability and that corroded casing can serve as a significant leakage path along the axis of a wellbore. The major components of corrosion found in the samples were different oxidation states of iron, but there was no discernable difference in the composition of corrosion products from specimens corroded by different mechanisms. Differences in cement porosity were observed in both experiments. We have shown that corroded casing is substantially permeable and a potential wellbore leakage pathway. Further, our results suggest that corrosion at the casing-cement interface may be affected by contamination in the cement slurry.A better understanding of corrosion mechanisms is essential for the remediation of leaky wells.

Impact of phthalocyanine structure as photosensitizer for ZnO nanophotocatalyst under natural solar irradiation

Novel composites of zinc oxide (ZnO) and copper phthalocyanines (CuTriPc and CuPc) were synthesized as efficient natural solar light photocatalysts for the photodegradation of organic wastewater pollutants. Spectroscopic and analytical measurements confirmed that both bulky triazolo copper phthalocyanine (CuTriPc) and unsubstituted planer (CuPc) were successfully coupled with ZnOnanoparticles. The synthesized nanocomposites were investigated as natural solar radiation photocatalysts toward the photodegradation of methylene blue (MB) analogue dye. The prepared CuTriPc/ZnO nanocomposite was proven to be an efficient solar light photocatalyst compared to pure ZnO and the unsubstituted CuPc/ZnO.

Materials characterization of TiO2 nanotubes decorated by Au nanoparticles for photoelectrochemical applications

The structural and chemical modification of TiO2 NTs by the deposition of a well-controlled Au deposit (0.01 mg cm−1) was investigated using a combination of microscopic (SEM, STEM), analytical measurements (XPS, SERS, UV-Vis, XRD) and photoelectrochemical investigations.