This paper provides an analysis of oil prices during and in the aftermath of the Global Financial Crisis, concentrating on the 2007-08 price spike and the 2014-16 price decline. The mildly explosive/multiple bubbles testing strategy by Phillips, Shi and Yu (2015, International Economic Review 56(4), 1043-1133) is used to test for price departures from an underlying stochastic trend and to assess whether any such departures can be explained by fundamentals or other proxy variables. The test dates two significant time periods in both Brent and WTI nominal and real front-month futures prices: a mildly explosive episode during the 2007-08 spike, prior to the peak of the Global Financial Crisis; and a significantly shorter, negative such episode during the 2014-16 price decline, whose commencement is dated around a key OPEC meeting in November 2014. Evidence using other commodity prices points to explanatory factors beyond commodity markets. A global economic activity proxy is found to be decisive in the episode in mid-2008; excess speculation is not. U.S. shale oil production, though contributing to the post-June 2014 price decline, is not seen to have been decisive. Against some recent work tying the CBOE Volatility Index (VIX) to oil futures prices, we find no evidence that the VIX decisively affected oil price levels during the sample period. The results are compared and contrasted with those obtained by Baumeister and Kilian (2016, Journal of the Association of Environmental and Resource Economists 3, 131-158) via a forecasting approach based on a structural vector autoregressive model without financial variables. Taken altogether, the results herein provide new evidence based on formal statistical testing that help resolve a number of recent controversies in the oil price literature.
<p style="text-align: justify;">Les interactions entre levures et bactéries lactiques sont déterminées par la nature des souches en présence, leur population et la constitution chimique du moût et du vin. Normalement, pendant la fermentation, les bactéries lactiques sont inhibées par les produits du métabolisme levurien. Mais dans certaines conditions, la croissance précoce des bactéries provoque une chute de la viabilité des levures et, par conséquent, un ralentissement ou un arrêt de la dégradation des sucres. Tous les mécanismes mis en jeu ne sont pas connus.</p><p style="text-align: justify;">+++</p><p style="text-align: justify;">ln wine-making, lactic acid bacteria succeed to yeasts to promote the malolactic fermentation (MLF), after the completion of the alcoholic fermentation. Yeasts are better adapted than bacteria to growth in grape must. So their development easily starts and the alcoholic fermentation triggers soon after the harvest. In the same time, the natural bacterial inoculum decreases, due to an antagonism between these two microorganisms. ln addition to ethanol, fatty acids synthesized by actively growing yeasts exert their toxic effect against lactic acid bacteria. At the end of the alcoholic fermentation, the remaining bacterial population (10<sup>4</sup> to 10<sup>3</sup> cell.p.ml) begins growing. It is mainly constitued by <em>Leuconostoc oenos</em> more resistant than lactobacilli. At that time, autolysis products from decline phase yeasts act as bacterial growth factors. Then, when the bacterial population is large enough (about 10<sup>6</sup> cell.p.ml) MLF happens. So, normally, MLF follows alcoholic fermentation within a few days. But in some conditions, the interactions between yeasts and bacteria do not work in this way. If the weather is particularly hot and dry during the last weeks of the maturation, the pH of the must may be high and generally sulfiting is lowered as there are no rotten grapes. Growing conditions are better than usually for bacteria that, in such a case, compete with yeasts. The bacterial population reach a sufficient level that can actually increase the yeast decline rate. Hydrolase activities of bacteria against yeast cell walls may occur. That leads to a fermentation stuck. These antagonism effects between yeasts and lactic acid bacteria in fermenting must control the wine-making process. Their extent vary with must composition even with both yeast and bacteria strains. Further research is needed to clear up involved machanisms.</p>
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