Grape composition affects wine flavour and aroma not only through varietal compounds, but also by influencing the production of volatile compounds by yeast. C9 and C12 compounds that potentially influence ethyl ester synthesis during fermentation were studied using a model grape juice medium. It was shown that the addition of free fatty acids, their methyl esters or acyl-carnitine and acyl-amino acid conjugates can increase ethyl ester production in fermentations. The stimulation of ethyl ester production above that of the control was apparent when lower concentrations of the C9 compounds were added to the model musts compared to the C12 compounds. Four amino acids, which are involved in CoA biosynthesis, were also added to model grape juice medium in the absence of pantothenate to test their ability to influence ethyl and acetate ester production. β-Alanine was the only one shown to increase the production of ethyl esters, free fatty acids and acetate esters. The addition of 1 mg·L −1 β-alanine was enough to stimulate production of these compounds and required for the stimulatory effect on ethyl and acetate ester production observed in this study.
Long-term scheduling for cascaded hydro energy systems is very important for low carbon energy production. It aims at determining the water release over a planning horizon to meet water resource requirements and the system demands for electric power. The problem is challenging in view of the complicated and stochastic system dynamics, nonlinear marginal cost, coupled hydraulic constraints, and the large problem size. In this paper we formulate the long-term scheduling problem of cascaded hydro energy systems with annual consumption and release constraints as a finite horizon constrained Markov decision process (CMDP), and develop a new rollout algorithm to optimize the policies. Numerical results demonstrate the effectiveness and the efficiency of the formulation and the new algorithm.Note to Practitioners-Long-term scheduling of cascaded hydro energy systems is an important planning activity in the reservoir management and electric industry. This paper formulates a long-term scheduling problem for cascaded hydro energy systems with annual water consumption and release constraints as a finite horizon CMDP, and develops a new rollout algorithm to deal with the large problem size. Motivated by a practical project on Yellow River in north China, this work has extended applicability since the new algorithm can start with any feasible policies currently used in practical systems and improve their performance. Numerical results demonstrate the effectiveness and efficiency of the formulation and the new algorithm.Index Terms-Cascaded hydro energy systems, constrained Markov decision process (CMDP), long-term scheduling, rollout algorithm.
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