Most glass jars, including common commercial food jars and standardized canning jars, are safe to clean in an automatic dishwasher. The annealed glass used in their construction generally tolerates the heat and water exposure of standard wash cycles. Ensuring the jar’s longevity and the appliance’s functionality requires understanding specific conditions and preparatory steps.
Glass Integrity and Thermal Shock
The primary risk to glass containers during the dishwashing process is a phenomenon called thermal shock. This occurs when a material experiences a rapid, uneven temperature change, causing differential expansion or contraction across its structure. If the resulting internal tensile stress exceeds the glass’s fracture limit, micro-cracks form and propagate, resulting in eventual breakage.
Standardized canning jars, often made from specialized tempered glass, are engineered to withstand the extreme temperature fluctuations involved in home pressure canning. These containers have thicker, more uniform walls and a specific annealing process that minimizes internal stresses. This makes them highly resilient to the dishwasher’s typical heat cycles, which rarely exceed 160 degrees Fahrenheit. Conversely, thin-walled decorative or inexpensive commercial jars may possess higher residual internal stress from manufacturing.
Less robust containers are susceptible to failure, particularly if loaded while cold from refrigeration and immediately subjected to a hot wash or heated dry cycle. To mitigate thermal failure, containers should stabilize to room temperature (ideally 68 to 72 degrees Fahrenheit) before being placed into the machine. Slow heating allows the glass structure to adjust uniformly, preventing the rapid localized stress accumulation that leads to failure.
Non-Glass Components: Lids, Labels, and Seals
While the glass itself is generally robust, non-glass components pose different challenges within the appliance’s high-pressure, high-heat environment. Paper labels and adhesives represent a significant risk to the machine’s internal mechanisms. As hot water and detergent dissolve the paper, small fragments can detach and flow through the system. These loose particles are prone to clogging the dishwasher’s filter screen or spray arm nozzles, compromising cleaning performance. Before washing, all paper labels and adhesive residue should be completely scrubbed away using hot water and a suitable solvent or abrasive pad.
Lids and sealing components also require careful consideration, especially those made from metal. Many standard jar lids are made from tin-plated steel, which is highly susceptible to oxidation and rust when exposed to prolonged moisture and aggressive detergents. This corrosion can weaken the lid and contaminate the wash load with rust flakes.
Rubber gaskets or plastic seals, often found inside two-piece canning lids, can degrade or warp when subjected to the prolonged high temperatures of a heated dry cycle. These materials lose their elasticity, compromising their ability to form an airtight seal necessary for long-term food storage. It is often recommended to hand wash these metal and rubber components in warm, soapy water to preserve their structural integrity and sealing capacity.
Preparing and Loading Jars for Optimal Cleaning
Maximizing cleaning effectiveness begins with proper preparation and placement of empty containers. All glass jars, especially those that held viscous or oily foods, should be thoroughly pre-rinsed or scraped to remove large food particles and residue. Pre-rinsing prevents heavy soil loads from exhausting the detergent’s capacity and prevents organic matter from forming blockages in the drain filter.
Proper loading technique is necessary to ensure the containers are thoroughly cleaned and remain stable throughout the wash cycle. Jars must be placed upside down, or inverted, on the bottom rack to allow the pressurized water jets to effectively reach the entire interior surface. Placing them on the bottom rack, rather than the top, also provides a greater margin against high heat and better secures the lighter items against the force of the spray arms.
Position the containers securely between the tines of the rack, preventing them from tipping over and blocking the spray pattern. Once the wash cycle is complete, promptly removing the containers is advised. Glass is prone to retaining heat and moisture. Allowing the jars to air dry completely, or wiping them with a clean towel, prevents hard water spots and reduces the risk of mildew growth before storage.