Many current home canning recommendations suggest a 5 to 10 minute wait at the end of the canning process prior to removing jars from the canner. Why is this wait time now included in some canning recipes and it is necessary for safety?Some home canning recipes, such as the Ball (Fresh Preserving) recipe for Classic Strawberry Jam, include as a final step these instructions: "Process jars 10 minutes, adjusting for altitude. Turn off heat, remove lid, let jars stand 5 minutes. Remove jars and cool 12-24 hours. Check lids for seal, they should not flex when center is pressed." Or, in the Ball Pressure Canning Guide, these instructions:  "Maintain the recommended pressure for the time indicated in tested preserving recipe, adjusting for altitude. Turn off heat. Let canner stand undisturbed (do not remove the weighted gauge) until pressure returns to zero. Wait 10 minutes, remove weight and unlock the lid, tilting away from yourself. Allow jars to cool for an additional 10 minutes. Remove jars and sit upright on a towel…."

This 5 to 10-minute weight time is not related to the safety of the process. Ball added this recommendation a number of years ago to their branded instructions (Ball, Kerr, Bernardin and Golden Harvest) because the company said that the waiting time increased the success rate or probability of lid sealing. The waiting time is designed to let the jar contents begin to settle as the heating rate starts to drop. The wait time may also help prevent jar breakage due to thermal shock.

Other sources have started to include the wait time in recipes to be consistent with Ball recommendations, for example (from the National Center for Home Food Preservation):

When the jars have been processed in boiling water for the recommended time, turn off the heat and remove the canner lid. Wait 5 minutes before removing jars to allow the canner contents to settle. This waiting period is not required for safety of the food when using USDA or University of Georgia processing times, however.

The 5- or 10-minute wait time is not included in print or online copies of the Wisconsin Safe Food Preservation Series bulletins; consumers may add this step, but it is not required. Use of the 5-minute wait time is not included in the Wisconsin Steam Canner Guidelines.

Here are some tips for increasing the success rate of jar sealing:

  • Use new, 2-piece lids. Lids that have sat in the cupboard for months (or years) are more likely to fail. Lids are 'one trip', they should never be reused.
  • Follow instructions for handling lids. Several years ago, major manufacturers stopped recommending a heat pre-treatment for lids. Pre-boiling these newer lids or even heating them to too high a temperature may be a cause of seal failure.
  • Apply 2-piece lids 'finger tip' tight. Do not over-tighten the screw band on 2-piece lids. Apply the band just until you meet resistance or 'finger tip tight.' A screw band that is too tight prevents air from leaving the jar and causes lids to buckle and fail to seal.
  • Manage canner temperature. Fluctuations in temperature within a canner, or keeping a canner temperature too high, may cause excess bubbling inside the jar, with food residue more likely to be deposited on the jar rim – a common cause of seal failure.

Even if you take all these precautions and your jars fail to seal, you may wish to contact the lid manufacturer.  Stay well and safe preserving. Barb