One of the most common applications of membrane filtration in the dairy industry is the treatment of whey from cheese manufacturers.
Cross flow ultrafiltration (UF) is the filtration technology most commonly used for processing of whey into high-value whey protein concentrates (WPC). The idea is to separate lactose and minerals from the protein, at the same time concentrating the protein by selecting a membrane which is permeable for lactose and which rejects protein. The more the whey is concentrated the higher the ratio of protein to dry matter (WPC) will be. The highest grade WPC achievable by concentration is approx. WPC70, meaning 70 % protein/dry matter. If higher-grade WPC is required, special techniques like diafiltration are needed to wash the protein, removing more lactose and minerals.
Fat and cheese fines are a natural part of whey; their presence sets a limit to the grade of WPC achievable. In order to produce a pure and almost fat-free WPC, the whey must be processed by microfiltration (MF). The purpose of MF is to separate native proteins, lactose and minerals from fat and very small particles (cheese fines).
By means of the MF step, the whey is separated into a low-fat/high-quality whey fraction, which can be processed by UF to produce high-quality WPC, WPI, and a fat fraction. The fat fraction also contains protein, which – together with the lactose – should be handled as a product in order to maximise the value of the whey.
In whey processing, the 94% water content is an obvious factor to consider, water being a crucial and limited resource in the dairy industry almost everywhere. The reverse osmosis (RO) technology has become widely used to remove water from whey. The water removed can be used for cleaning or other process steps. Apart from reducing the need of drinking water for production, this considerable volume reduction of the whey stream provides an obvious cut in transportation costs and environmental load, if the product is transported to another production site.