Any amateur wine maker will tell you that producing a decent batch is a balancing act between yeasts and sugar to produce the right kind of reaction and the best result.
It’s a ‘live’ product that must be controlled. Any residual yeast remaining after fermentation can cause unwanted refermentation while residual sugar can produce carbonation. The undesired presence of bacteria such as acetobacter can be disastrous by turning wine into vinegar.
Drew Horton, Enology Specialist at the University of Minnesota, said: “If a volume of wine has any residual sugar – and you’re not diligent about removing all the bacteria, and more importantly, the yeast
cells – the wine can referment in the bottle.
“It’s a disaster because it causes the wine to get bubbly or cloudy, or the cork pushes up, or in the worst scenario, the bottles start exploding.”
Microbiological stabilisation
The solution lies with filtration throughout the process to produce wine with the required quality, flavour and aroma while microbiological stabilisation eliminates yeasts and bacteria that can destroy the taste. Several methods are available. Common techniques include flat sheet filtration, a traditional technique still used by small wineries. This method has more recently been adapted into lenticular modules assembled in an enclosed housing which avoid drip losses and provide additional flexibility, hygiene and ease of use.
Diatomaceous earth filtration which uses skeletons of microscopic water plants called diatoms has now largely been replaced by crossflow filtration, a separation method where a particle-containing fluid passes tangentially along the surface of a membrane filter.
Media smaller than the pores of the membrane pass through the filter while larger components are retained and move along the surface before being swept away. Advantages include a reduction in wine loss, less waste and lower labour costs.
Most crossflow filter technologies use polymeric membranes made of polypropylene, polysulfone, polyvinylidene fluoride or other typical membrane materials.
As such, the operating environment of the crossflow technology may be limited by the temperature tolerance or material compatibility. Filtration process Companies such as US-based Graver Technologies have developed a range of products for each stage of the filtration process in wine making.
These include polypropylene and microfiber glass filters such as the QMC which has been tested to prove the reliable removal of larger organisms during primary clarification. During storage or transport ongoing fermentation can occur while other contamination is possible for example through tank vents. Carbonation gas impurities can also negatively affect the consistency of sparkling wines. Graver Technologies’ TefTEC filter effectively sterilizes gases and removes sub-micron contaminants. At the end of the process, final membrane filters such as the ZTEC-B remove organisms such as Dekkera intermedia, Lactobacillus brevis, and Leuconostoc oenos.
Higher temperatures
Crossflow filtration requires technology that can withstand the higher temperatures and aggressive chemicals use in wine production. Graver Technologies’ Scepter range features membrane tubes welded together into all-stainless steel module assemblies with no gaskets, O-rings or polymeric components. This enables ease of cleaning, durability and compatibility.
Other companies such as US-based Donaldson take a different route by offering one kind of filter. Its LifeTec Absolute filter includes elements with 20% more media than comparable filters with a triangular shape designed to stay intact under high flow rates. While designed to remove organisms in one filtration step, pre-filtration is usually necessary to save costs. The LifeTec filter is reusable and its strong cage structure is made to withstand the rigors of steam sterilization, again reducing costs.
Colter Marcks, lead engineer for Process Filtration at Donaldson, said: “Filter one is capturing the bulk of the contaminant and making sure the final one doesn’t get blocked up as quickly. Because a membrane filter is more expensive, you try to do most of the work with the first one. “Once you’ve worked in a winery and 200 cases of wine are either cloudy or refermenting and you have to pull in a crew of extra people to pull every cork, dump the wine back into a tank and restabilize, refilter, and rebottle them, you swear you’ll never let it happen again.”
