Canning 101: Fruit Float

Recently one of our readers asked us, “When canning strawberries or peaches in syrup, or even tomatoes packed in water, why do they float in your jars?”   We thought this was a great question that required an explanation.

Many of us have experienced fruit float when canning whole fruits and some vegetables.  It’s not attractive and if given a choice we’d probably all prefer if our fruit co-operated and did as it’s told…that is sink to the bottom, submerged in liquid.  But, sometimes this just doesn’t happen and we are left wondering “Why?  Is it safe to eat?  And, what could we have done to prevent it?’ 

Firstly, the good news, it is perfectly safe to eat.  Fruit float will not affect the taste or the shelf life of the preserve (as long as proper canning practices were followed).  But, don’t you still wonder why it happens and if there is anything that can be done to prevent it? 

Here are a few suggestions that may help to prevent future buoyancy problems.

1. Select fruit that is fresh, firm, unblemished, and ripe.  A few years back, we purchased multiple boxes of peaches that were seconds.  At half the price we thought it was a steal but they caused us 10 times more grief and ended up floating like crazy. They were all at different stages of ripeness with bruised areas which made it challenging to slip off the skins.  Plus, over ripe fruit does not absorb enough sugar causing them to float in the jars. 
2. Use the hot pack method.  While both the hot pack and cold pack methods are used to can whole fruits and vegetables, the hot pack method may help to prevent fruit float.  The hot pack method requires the fruit to be heated through before packing into hot sterilized jars.  This method helps to expel the air that all fruits contain, making them more dense and less likely to float to the surface.  Heating them through also shrinks the fruit (slightly) allowing jars to be packed tightly; again, helping to prevent the fruit from floating.  The cold pack or raw pack method of preservation allows fruits and vegetables to be packed without heating but it requires a longer processing time.  During processing, the air in the fruit or vegetables will be cooked out causing them to shrink in size and create more room in the jars which allows them to float to the surface.
3. Packing jars.  Be sure to pack the fruit tightly in each jar without crushing the pieces.    Remove all air bubbles and top up with additional fruit and/or liquid.  Some shrinkage will occur during processing so fruit that is well packed in each jar is less likely to have the space and/or room to float.
4. Sugar content.  Some fruits like apricots, rhubarb, and berries naturally have more air in their cells which makes them more buoyant.  Coating these fruits in sugar and setting aside allows the fruit to absorb the sugar and expel some of the water to make the fruit more dense.   Heavier, more sugary syrups may cause fruit to float.  Why?  Light syrup, juice syrups, or water packed fruits/vegetables are in an environment where the fruit/vegetables are equally as dense as the liquid, diminishing buoyancy.  Fruit in a heavier syrup  is lighter than the liquid and therefore may float.  Note: We pack 90% of our fruits in a very light syrup and will still occasionally experience fruit float. 
5. Follow processing times carefully.  Over processing fruits and vegetables will destroy cell structure, making fruit lighter and more likely to float.

Although, it may be impossible to prevent fruit float every time, the above suggestions should help.  And, sometimes understanding why something is happening is enough.

The peaches on the left are fine but both the strawberries (center) and the plums (left) have fruit float.  But, we guarantee they all taste yummy!