Membrane separation processes in the wine industry: Recovery of caustic cleaning solutions and juice preservation

Formulated caustic cleaning solutions are used in wineries for clean-in-place (CIP) purposes. Presently, spent cleaning solutions are disposed of after only a single use. This is a waste of potentially reusable cleaning solutions. The present work investigated the effectiveness of using membrane separation processes to recycle spent formulated cleaning solutions. The membranes tested were 30,000 molecular weight cut off (MWCO) ultrafiltration membranes, 10,000 MWCO ultrafiltration membranes, and 2,000 MWCO nanofiltration membranes. To simulate the fouled surfaces in a commercial winery, a mock wine solution was used to foul stainless steel tanks. The solution contained 500 mL of wine lees, 1.26 L of ethanol, 55 g of KOH pelletes, 88 g of tartaric acid, and approximately 7 L of de-ionized water. Spent cleaning solutions were subjected to ultrafiltration or nanofiltration. The permeates from the filtration process were used to clean fouled tanks. Relative Light Units (RLU) counts, which are a measure of adenosine tri-phosphate (ATP), were used as the main criterion for determining the effectiveness of the recycled cleaner. An instrument, Biotrace Unilite Xcel, in conjunction with swabs, was used for the RLU test. Tanks cleaned by recycled cleaning solutions were swabbed for RLU. The threshold for cleanliness was RLU 800. Any number below this threshold was considered clean; whereas any number above this threshold was considered dirty. Besides RLU data, Chemical Oxygen Demand (COD) and Total Suspended Solids (TSS) for each membrane were also measured. The results for RLU were inconclusive in the present work because the RLU counts for the fouled tanks were low to begin with. The COD and TSS data were then used to determine the most effective membrane in recycling formulated caustic cleaning solutions. Based on COD rejections, nanofiltration was determined to be the most effective membrane process with an average rejection of 0.33 compared to 0.075 for 10,000 MWCO ultrafiltration. 30,000 MWCO ultrafiltration was not effective in rejecting COD.; The ability to preserve grape juice so that fermentation could be delayed would benefit wineries as they could initiate fermentation throughout the year rather than only during harvest. Ultrafiltration was used to filter yeasts, molds, and bacteria from grape juice. The present work was to analyze the microbial growth, free SO2, residual sugar, and pH of the grape juice that had been stored for 6 months. The present work found that there was no yeast or mold growth in the filtered juice, but there could have been bacteria growth. The properties of the grape juice were found to have stabilized and were ideal for making a quality wine: free SO2 had an average of 25 ppm for the samples tested, residual sugar had an average of 22 0Brix, and the pH of samples was approximately 3.5.