The effect of Yeast Strain, Grape Solids, Nitrogen and Temperature on Fermentation Rate and Wine Quality

The effect of four yeast strains, two levels of grape solids, two nitrogen levels and three fermentation temperatures viz. 10°, 13° and 15° C on total fermentation time (TFT) and wine quality was studied in a factorial experiment by employing a nitrogen deficient Chenin blanc must. It was found that the presence of solids, addition of nitrogen and fermenting at 15° C decreased TFT dramatically. Nitrogen was the only factor which also increased wine quality, the other two having a detrimental effect. At optimum levels of nitrogen, yeast strains WE 452 and WE 500 (VORI collection) reduced TFT without detrimentally affecting wine quality. In the case of WE 452, no solids should be present and fermentation conducted at 10° C -13° C, and in the case of WE 500, traces of solids should be present and a fermentation temperature of between 13° C - 15° C should be utilized. Under these conditions WE 452 and WE 500 reduce TFT from C.76 days to as few as C.30 and C.15 days respectively

Array-based iterative measurements of SmKS travel times and their constraints on outermost core structure

Vigorous convection in Earth's outer core led to the suggestion that it is chemically homogeneous. However, there is increasing seismic evidence for structural complexities close to the outer core's upper and lower boundaries. Both body waves and normal mode data have been used to estimate a P wave velocity, V_p, at the top of the outer core (the E’ layer), which is lower than that in the Preliminary Reference Earth Model. However, these low V_p models do not agree on the form of this velocity anomaly. One reason for this is the difficulty in retrieving and measuring SmKS arrival times. To address this issue, we propose a novel approach using data from seismic arrays to iteratively measure SmKS-SKKS-differential travel times. This approach extracts individual SmKS signal from mixed waveforms of the SmKS series, allowing us to reliably measure differential travel times. We successfully use this method to measure SmKS time delays from earthquakes in the Fiji‐Tonga and Vanuatu subduction zones. SmKS time delays are measured by waveform cross correlation between SmKS and SKKS, and the cross‐correlation coefficient allows us to access measurement quality. We also apply this iterative scheme to synthetic SmKS seismograms to investigate the 3‐D mantle structure's effects. The mantle structure corrections are not negligible for our data, and neglecting them could bias the V_p estimation of uppermost outer core. After mantle structure corrections, we can still see substantial time delays of S3KS, S4KS, and S5KS, supporting a low V_p at the top of Earth's outer core

Seismic probes of solar interior magnetic structure

Sunspots are prominent manifestations of solar magnetoconvection and imaging their subsurface structure is an outstanding problem of wide physical importance. Travel times of seismic waves that propagate through these structures are typically used as inputs to inversions. Despite the presence of strongly anisotropic magnetic waveguides, these measurements have always been interpreted in terms of changes to isotropic wavespeeds and flow-advection related Doppler shifts. Here, we employ PDE-constrained optimization to determine the appropriate parameterization of the structural properties of the magnetic interior. Seven different wavespeeds fully characterize helioseismic wave propagation: the isotropic sound speed, a Doppler-shifting flow-advection velocity and an anisotropic magnetic velocity. The structure of magnetic media is sensed by magnetoacoustic slow and fast modes and Alfv\'{e}n waves, each of which propagates at a different wavespeed. We show that even in the case of weak magnetic fields, significant errors may be incurred if these anisotropies are not accounted for in inversions. Translation invariance is demonstrably lost. These developments render plausible the accurate seismic imaging of magnetoconvection in the Sun.Comment: 4 pages, 4 figures, accepted Physical Review Letter

Triadimef on, a Systemic Fungicide Against U ncinula N ecator (Oidium) on Wine Grapes: Disease Control, Residues and Effect on Fermentation and Wine Quality

The efficacy of the systemic fungicide triadimefon (l-(4-chlorophenoxy)-3,3-dimethyl-l(lH-1,2,4-triazol-1-yl)-2-butanone as a wettable powder spray was evaluated against oldium in field trials. At a high level of infection (86,2% infection), treatment of the grapes with vine sulphur was inadequate (65% infection), while the triadimefon treatment controlled the disease excellently (10,5% infection). Residues recovered from grapes were low, in the order of 0,245 mg/kg on grapes harvested immediately after the final application of the fungicide. Addition of 200 mg triadimefon (active ingredient)/ f, to grape juice had no significant effect on either onset or rate of fermentation. Fermentation of must from triadimefon-treated grapes was also similar to that of must from untreated grapes, and no effect on wine quality could be observed

Sorbic Acid as a Wine Preservative-Its Efficacy and Organoleptic Threshold

Sorbic acid was added to wines in different concentrations to determine its effect on the inhibition of yeasts in semi sweet wines. Sorbic acid proved to be an effective inhibitor of yeast growth when used at a concentration of 200 mg/C in conjunction with a concentration of 100 mg 802/C. As the sorbic acid does not kill the yeast cells but only inhibits them it is imperative that the wine should still be filtered as sterile as possible.Sweet must should not be preserved with sorbic acid because of the danger of bacterial spoilage and the subsequent development of the so-called "geranium" odour in the wines sweetened with infected sweet must. The flavour threshold of sorbic acid itself in dry wines was determined to be between 300 and 400 mg sorbic acid/€. This is virtually double the amount recommended for inhibition, at which concentration no effect should be (nor was) encountered on the quality of the wine

Effect of Copperoxychloride on the Fermentation of Must and on Wine Quality

A Chenin blanc and a Colombar vineyard was sprayed with copperoxychloride (CuOCI) in different spraying programs. A laboratory trial was conducted where copper in different concentrations was added to grape must and fermented. Copper concentrations were determined in musts and wines, fermentation curves established and wine quality assessed. Results show that spraying a vineyard with CuOCI for 5 or 6 consecutive sprays up to 14 or 3 days beforeharvest respectively caused copper concentrations of 13-44 mg// in the settled musts. Spraying a vineyard at 14 + 7 + 3 days before harvest yielded a must with a copper concentration of 16 mg//. These musts as well as a must to which 10 mg/ I of copper was added, underwent slower fermentation than their respective controls. Wine quality was seriously impaired. It is concluded that the closer to harvest the last copper spray is applied, the more problems will be encountered

Metaxanine, A Systemic Fungicide Against Plasmopara Viticola on Wine Grapes: Disease Control, Residues and Effect on Fermentation and Wine Quality

The systemic fungicide metaxanine/methyl D, L-N-(2,6-dimethyl-phenyl)-N-(2 methoxyacetyl) alaninate/, was compared with mancozeb for the control of Plasmopara viticola (B x C) Berl. & de T. on grapevines in the Western Cape Province of South Africa. The systemic fungicide gave better control thanmancozeb. Good control was obtained with applications of the systemic fungicide at 21 day intervals, despite the fact that weather conditions were particularly favourable for disease development. Residues of metaxanine recovered from grapes were low and did not affect either the onset, or the rate of fermentation of grape juice, nor did it affect wine quality

Killer Factor in Wine Yeasts and its Effect on Fermentation

The occurrence of killer factor amongst yeast strains in the Viti cultural and Oenological Research Institute (V 0 RI) yeast collection was studied. From a total of 96 strains, 85 were Saccharomyces cerevisiae of which 7 strains were killer, 9 neutral and 69 sensitive. These included some imported strains. On agar, no killer action was detected at wine pH. In fermentation studies using four grape cultivars, it was shown that where the killer yeast population was less than approximately 2,5% fermentation was not affected. At higher levels the killer yeast, in some instances, took over and completed fermentation, but the total fermentation time was never longer than that of the killer strain on its own. It was concluded that the use of a yeast strain should not hinge on its killer character but rather on its oenological characteristics

The Effect of Fermentation Time (as Induced by Fermentation and Must Conditions) on the Chemical Profile and Quality of a Chenin blanc Wine

Pattern recognition and simple factorial analyses were applied to chemical profiles determined on wines resulting from an experiment in which the effect of grape solids, assimilable nitrogen, bentonite and fermentation temperaturelevels as well as culture aeration on total fermentation time was investigated. It was found that fermentation times of the untreated Chenin blanc must could be shortened considerably by increasing grape solid levels and/ or nitrogen as well as temperature. However, it was established that the speeding up of fermentation at sub-optimal assimilable nitrogen levels leads to wines relatively high in higher alcohols and low in esters

Ergosterol Concentration of Several Different Saccharomyces cerevisiae Yeast Strains

Differences in the formation of ergosterol in yeast cells have been found amongst several wine yeast strains used in South Africa. A higher ergosterol content is generally accompanied by a faster fermentation rate and results in a shortening of fermentation time. A high ergosterol concentration in the cell is not a prerequisite for maximal cell formation, but probably affects the metabolic activity of the cell. Aeration of the must during the yeast proliferation stage, brought about marked increases in ergosterol concentrations