Department of Chemical Engineering, University of California, Davis, California.
Department of Viticulture and Enology, University of California, Davis, California.
Biotechnol Bioeng. 2019 Apr;116(4):781-792. doi: 10.1002/bit.26874. Epub 2019 Jan 16.
Red wine fermentations are performed in the presence of grape skins and seeds to ensure the extraction of color and other phenolics. The presence of these solids results in two distinct phases in the fermentor, as the solids float to the top to form a "cap." Modeling of red wine fermentation is, therefore, complex and must consider spatial heterogeneity to predict fermentation kinetics. We have developed a reactor-engineering model for red wine fermentations that includes the fundamentals of fermentation kinetics, heat transfer, diffusion, and compressible fluid flow. To develop the heat transfer component of the model, the heat transfer properties of grapes were experimentally determined as a function of fermentation progression. COMSOL was used to solve all components of the model simultaneously utilizing a finite element analysis approach. Predictions from this model were validated using prior experimental work. Model prediction and experimental data showed excellent agreement. The model was then used to predict spatial profiles of active yeast cell concentration and ethanol productivity, as well as liquid velocity profiles. Finally, the model was used to predict how these gradients would change with differences in initial bioavailable nitrogen concentration, a key parameter in predicting fermentation outcome in nitrogen-limited wine fermentations.
红葡萄酒发酵是在葡萄皮和种子的存在下进行的，以确保颜色和其他酚类物质的提取。这些固体的存在导致发酵罐中出现两个明显的阶段，因为固体浮到顶部形成“帽”。因此，红葡萄酒发酵的建模非常复杂，必须考虑空间异质性来预测发酵动力学。我们开发了一种用于红葡萄酒发酵的反应器工程模型，该模型包括发酵动力学、传热、扩散和可压缩流体流动的基础。为了开发模型的传热部分，我们通过实验确定了葡萄的传热特性作为发酵过程的函数。我们使用 COMSOL 通过有限元分析方法同时求解模型的所有部分。该模型的预测结果通过先前的实验工作进行了验证。模型预测和实验数据吻合得非常好。然后，该模型用于预测活性酵母细胞浓度和乙醇生产率的空间分布以及液体速度分布。最后，该模型用于预测这些梯度如何随着初始生物可利用氮浓度的差异而变化，氮浓度是预测氮限制葡萄酒发酵结果的关键参数。
