Controlled fermentation in wine production by BUCO heat exchanger plates
BUCO heat exchange plates have the highest normalised coefficient k (W/(K.mbar)) in terms of pressure loss per unit area (mbar/m²) over the entire flow range, especially at low flow rates, which are the most interesting economically. Heat exchanger plates can be manufactured in almost all possible geometries and stainless steels used in wine production. The welding processes for heat exchanger plates are either laser or resistance welding. Here, laser-welded seams have a rougher surface than resistance-welded seams and are therefore more difficult to clean, which brings with it the risk of bacterial growth.
Controlled wine fermentation has become increasingly important internationally. In order to evaluate this required technology, it is necessary to determine the equipment and operating costs involved in using the BUCO heat exchange plate as a heat exchanger in this area. A survey of winegrowers‘ experiences with this technology was conducted. The summary of the investigations can be summarised in the following points:
- Controlled fermentation through active cooling increases the quality of the product.
- The most economical and effective active cooling is achieved by BUCO heat exchanger plates inside the tank.
- The transfer coefficient k (W/(K.mbar)), which is given in relation to the pressure loss per unit area (mbar/m²), is the most important parameter in measuring economic efficiency.
- BUCO plates have the highest normalised coefficient k (W/(K.mbar)) in relation to pressure loss per unit area (mbar/m²) in the whole flow range, especially at low flow rates, which are the most interesting economically.
- Controlled fermentation has the least negative impact on the environment.
- The refrigeration plant can be operated either by absorption or by compression, depending on the types of energy available and the needs of the customer.
In contrast to warm climate countries such as South Africa, Australia, France, Chile, Argentina, etc., where temperature-controlled fermentation has been standard practice for several decades, the subject of controlled fermentation in oenology has only been an issue in Europe for two decades. The reasons for this were the low autumn temperatures and the low tank capacity in many small, family-run wineries, as well as the initial solutions of surface irrigation of the fermentation tanks used here. Controlled fermentation maximises aroma formation and positively influences fermentation metabolism (e.g. loss of aroma due to release of dissolved gases such as carbon dioxide – stripping effect. It is internationally recognised that lowering the fermentation temperature to 20°C leads to a great increase in quality. Another aspect to consider with active cooling is the ecological aspect.
The transfer surface for lowering the fermentation temperature can be provided by external heat exchangers, double-shell tanks or exchange surfaces within the tank (e.g. inserted heat exchanger plates). External heat exchangers are not suitable for the fermentation phase as the wort must be pumped through the heat exchanger. Double-jacket heat exchangers are rarely used because it is not always possible to modify the existing tanks due to the thin walls. In addition, the ambient temperature must be close to the temperature of the water circuit.
With double shells, the exchange area is very limited. In practice, with small tanks only the upper half of the tank is available for cooling, which is thus strongly dependent on the fill level of the tanks. In addition, a temperature gradient forms depending on the radius and height of the tank. The advantage of this technique is that the inside of the tank is not clogged by equipment, making cleaning quick and easy. Considering all these arguments, the heat exchanger plates in the tank are the best alternative. In the past, a number of measurements were carried out with some types of plates. These measurements were carried out in a tank with a square cross-section containing alternating fermenting wort and water, under the action of a reel stirrer.
It turned out that the values achieved with water were 2 to 3 times higher than those achieved with fermenting wort. The reason for this was that the flow conditions were too good due to the use of an agitator. Taking previous experience into account, an attempt was made to simulate the typical flow conditions of the fermentation phase. Nevertheless, compared to the previous results, the reference plate achieved values that were about 15 % higher than could be expected when using fermenting wort. The BUCO heat exchange plate has the best transfer coefficient, but also the highest pressure loss per unit area Dp/A. This shows the importance of the given coefficient k as a function of the pressure loss normalised to the area Dp/A, as it indicates how much kW of heat power can be transferred per kW of mechanical power in the pump.
Heat exchanger plates can be produced in almost all possible geometries and stainless steels used in wine production. The first tests for cleaning dirty plates showed that electropolished plates are the easiest to clean. The surface finish closest to electropolishing can have good cleaning performance, while the surface finish of cold rolled plates is not recommended. The welding processes for heat exchanger plates are either laser or resistance welding. Here, laser-welded seams have a rougher surface than resistance-welded seams and are therefore more difficult to clean, with the risk of bacterial growth.
Our evaluation of the economic efficiency of a controlled fermentation system shows that its costs are about 2.5 times higher than those of a system with surface irrigation of the tanks. The starting points for this evaluation were a small plant with 12 kW cooling capacity, a 10-year depreciation and a simple control system. Only the savings in wastewater costs were considered, i.e. the increase in profit due to the higher product quality was not taken into account in this analysis; this is where the real incentive for implementing controlled fermentation lies.
The savings in fresh and waste water costs as well as the increase in wine quality justify the use of a cooling system for controlled fermentation. The selection of the various components of a controlled fermentation system is determined by the individual circumstances of each winery.
We have always assimilated engineering science and thermodynamics optimally in the various manufacturing processes.
Thermodynamicists,mechanical engineers and welding engineers define the dimensioning, design and construction of customised heat exchanger panels and systems in materials ranging from mild and austenitic steels through to titanium, and ensure successful distribution of their work worldwide.
In doing so they fall back on production engineering expertise and calculations developed in the course of the past hundred years that are still being continuously optimised in an ongoing process.
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