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We pulled about two gallons of grapes off the vine. I ran them through a juicer and put the juice into gallon jars, sealed them and put them in the refrigerator. The next morning, we opened the fridge and found that it had fermented and ran all over. Can I still make jelly out of this or do I throw it away? Why did this happen? What did I do wrong?

It appears that your grapes did what grapes have been doing naturally for as long as anyone knows – fermenting. Even at refrigerated temperatures the wild-type yeasts that are naturally present on almost all grapes can grow and convert the sugar in the grape juice to alcohol. You may also have added yeasts or other microorganisms to the juice from the juicer, or in the jugs. Here are some suggestions for preventing this in the future:

Pay careful attention to the cleaning and sanitizing of the juicer and jugs you use to store the juice. Wash all equipment with warm soapy water, then soak the washed equipment in a sanitizing solution such as sulfite (see below) or one tablespoon household bleach in one gallon of water. Allow the equipment to soak for at least one minute. Do not leave metal parts in the bleach solution for much longer than one minute, since bleach water is somewhat corrosive. It is also a good idea to use gloves to protect your hands from the bleach water. Allow the equipment to air-dry and use within about one hour of sanitizing.

Most modern winemakers use sulfite to sanitize equipment and inhibit the growth of these wild-type yeasts in juice. Sulfite can be purchased at stores specializing in home winemaking or brewing, or on the Internet. The sulfite will come with instructions for its use.

Another way to prevent fermentation would be to heat the juice to about 165F for 15 seconds (bringing the juice just to a simmer would accomplish the same thing) and then put in sanitized jars. This is something like the process of pasteurization used commercially for juices and milk products.

As for using the juice to make jelly, there is no safety reason that would prevent you from making jelly out of the juice. In fact, it is possible to make jelly out of fully fermented grape juice (wine). (I frequently make wine jelly at Christmas time. You can put the finished jelly in cheap wine glasses, seal with paraffin, tie a ribbon around the stem of the glass and have a great impromptu gift.) However, the flavor will be different than you might expect. If you want to try this, follow the directions for the type of pectin you like best. I might add just slightly more sugar than the recipe calls for to take in account the sugar that has been lost due to the action of yeasts. The process of cooking the jelly will remove any alcohol from the juice.


Douglas L. Holt, Ph.D., Chair, Food Science and Extension Specialist, University of Missouri-Columbia






Last update: Tuesday, May 05, 2009



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