Technical Yearbook 2023

JANUARY/FEBRUARY

Filtration choices By Charl Theron

Consumers do not like bottled wines containing hazes, turbidity, sediments or crystals; as such processes need to be applied to remove these before bottling. Filtration is one of the processes that can be used to ensure clarity. Unfortunately, no single filtration technology can be used for all purposes. A choice must be made as to which technology will be the most suitable. Different factors like the stage of winemaking, the nature of the solids that must be removed, the required filtration rate, the volume of product to be filtered and the purpose of filtration can influence this choice. To make the decision, the different filtration technologies need to be understood. Diatomaceous earth Diatomaceous earth (DE) filtration removes coarse gelatinous and deformable material. Diatomaceous earth is a sedimentary product consisting mainly of silica. It is mined as the fossilised remains of diatoms. It is usually used in the beginning phases of winemaking. Various solids like yeast, bacteria, suspended solids and colloids can be removed. Due to the irregular packing of the diatoms, a complex matrix with high porosity is created. Pores within and between the DE cells are so tiny that even small particles can be removed. DE filtration can be used on its own or as a second filtration phase. Screens or pre-filters can be used to eliminate larger particles before DE filtration. For brilliant clarity, it is recommended that filter aids are used together with DE. Mineral filter aids like diatomite and perlite are preferred for removing gross solids, like yeasts and proteins. Crossflow filtration Crossflow filtration (CFF) uses internal pressure when the wine is pumped into a membrane element at a high linear speed to force water, dissolved compounds and solvent through the membrane layer. This is a clear, transparent filtrate called the permeate. The insoluble suspended material, bacteria, yeast and macromolecular compounds cannot pass through the membrane and are called the retentate. The retentate circulates back to the membrane element. By selecting the pore size, specific particles can be removed. The CFF membrane is made of highly stable oxides. It has excellent chemical stability, high reliability and economic advantages and is considered green technology.

The different pore sizes can be used for microfiltration, ultrafiltration or nanofiltration. Ceramic membranes have pore sizes ranging from 50 - 1 200 nanometres (nm) for microfiltration, 10 - 50 nm for ultrafiltration and 1 - 10 nm for nanofiltration (1 nm = 10 -9 metre). Ceramics have many advantages, including strong acids and alkali resistance, excellent oxidation stability, high solvent stability and thermal stability up to 500°C. It has a long work life, easy regeneration and stable performance. It is possible that the latest ceramic technology could replace centrifugation.

Crossflow filtration.

Titanium membranes Titanium membranes have established a good reception for fine filtration. Trials showed that titanium membranes could run 24 hours daily for a week compared to polymeric or ceramic filters, which may need up to 30% in cleaning modes. Titanium membranes can be cleaned with hot water in minutes, and larger titanium filters can run at a filtration rate of 35 000 - 40 000 L per hour. Titanium membranes have an adjustable micron rating ranging from 0.1 micron for E. coli or bacteria removal, 0.2 micron for white wines and 0.4 - 0.45 microns for red wines. The titanium membrane technology is suitable for the wine industry but is also transferable to other industries. In conclusion, different filtration types are available to remove particles of macro size down to the molecular level.  Reference https://www.wineland.co.za/filtration-choices/

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TECHNICAL YEARBOOK 2023