The inability of your dishwasher to remove tea stains from cups while a simple rub with a dish sponge can do the job is likely due to a combination of factors related to the dishwasher's cleaning process and the nature of tea stains:
Type of Stains: Tea stains can be quite stubborn, especially if they have dried and become more set into the surface of the cup. Dishwashers are generally effective at removing most food residues, but certain stains may require more specialized cleaning.
Water Temperature and Soaking Time: Dishwashers use hot water during their cleaning cycles, but the water might not be as hot or the soaking time as long as when you hand wash dishes. Hotter water and longer soaking times can help break down and loosen tough stains.
Direct Contact and Agitation: When you hand wash dishes, you can directly target the stained areas with a dish sponge and apply more pressure, resulting in better mechanical action to remove the stains. Dishwashers rely on water jets and the circulation of water to clean dishes, which may not have the same targeted cleaning power for specific stains.
Detergent and Cleaning Agents: The type and effectiveness of the dishwasher detergent you use can also play a role. Some detergents are formulated to handle specific stains better than others. Additionally, hand washing often allows you to use more concentrated cleaning agents on stubborn stains, whereas dishwasher detergents are designed for overall cleaning.
Placement and Positioning: The positioning of the cups in the dishwasher's racks can also affect the cleaning efficiency. If the stained areas are not exposed to the water jets properly, the dishwasher might not be able to remove the stains effectively.
To improve the dishwasher's performance in removing tea stains and other tough residues:
Pre-Rinse: If your dishwasher has a history of struggling with certain stains, you can consider giving the dishes a quick pre-rinse before loading them into the dishwasher.
Scrape Off Excess: Remove any large food particles or debris from dishes before loading them into the dishwasher.
Check Water Temperature: Ensure that your dishwasher's water heating element is functioning correctly, as hotter water can improve stain removal.
Use High-Quality Detergent: Invest in a high-quality dishwasher detergent that is known for effective stain removal.
Load Dishes Properly: Arrange dishes so that stained areas are exposed to the water jets for better cleaning.
By making these adjustments and continuing to hand wash tough stains if necessary, you can achieve cleaner dishes and cups overall.