Wine Filtration
Filter Performance
Given the wide array of products available on the market, it is important to understand filter removal performance to ensure their effective and economical use in winery applications. Common terms used to loosely define filter particle removal performance are nominal and absolute. These terms refer to the removal solely of particles and should not be used to describe filters used for bacteria and yeast removal. However, these terms are also extremely relative, and do not specify true particle removal performance. Instead, filter removal efficiency based on particle counts, or the beta-ratio can be used to quantify and compare filter performance.
Nominal
A nominal pore size rating describes the ability of the filter media to retain the majority of particulate at (usually 50-90%) the rated pore size in microns. In other words, a filter that is rated as a 5-micron at 85 percent can be expected to remove 85 percent of the particles that are 5 microns or larger from the wine that passes through it.
Absolute
Absolute filters receive their name from the fact that the filtration is absolute since any particle that is larger than their pore size will be retained on the surface of the filters. Absolute filters have a specific rating of membrane efficiency independent of flow rate and pressure differential. This is a much more reliable means of assessing a filter for an application as its performance is more repeatable.
Beta Ratio
Beta ratio is often used when expressing filter efficiency for a given particulate size. This, in simple terms, is the number of particles in the upstream (before filtration) divided by the number of particles downstream (after filtration). For example, if a 3-micron filter element has 5,000 particles upstream and allows 5 particles through its media, it's beta-ratio would be calculated as 5,000 (upstream) / 5 (downstream) = beta1000.
Log Reduction Value
A log reduction value (LRV) is another term used for expressing filter efficiency at reducing yeast and bacteria. The log reduction value equals the number of organisms in the influent divided by the number of organisms in the effluent (filtrate). For example, if the number of colonyforming units (CFU) in the control was found to be 1,000,000 (or 106) and the end result using the product was only 1,000 (103), that would be a log reduction value of 3 or a reduction of 99.9%.
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