Wine Wizard replies: The short answer to your question is: 0.45 micron nominal filter pads are the industry standard for “sterile” filtration. These pads prevent all yeast and bacteria from getting through. So, if you want to be as certain as possible, it’s best to filter with a 0.45 micron nominal pad. This will ensure that you take out the maximum amount of unwanted material. The 0.5 micron filter sheet is a little bit “looser” than the 0.45 micron sheet and would most likely allow some microbes to pass through. If I was a winery with 50,000 gallons of 1% RS (residual sugar) Chardonnay that I wanted to bottle and put into the market, I would certainly make sure to final-filter with the tightest pads possible. Ruining thousands of customers’ opinions about your products due to one little yeast cell is a scary prospect. However, as you might imagine, I’ve got a longer answer for you and you can choose what option best suits you. You’re a home winemaker with only 65 gallons of the 1% RS Chardonnay, not 50,000
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