If a blender is only used for cold items, and kept extremely clean, could it be used with dairy ingredients (like a smoothie), and also for pareve items that will be served with meat (like hummus served at a Shabbat meal)? Thanks!
There's a standard procedure established for cleaning materials and surfaces for proper Kosher kitchens.
While you are logically consistent by believing that there is no issue mixing a parve item with a dairy item, the issue gets complicated when we are discussing food surfaces and preparation.
You stated at the end that you use this dairy blender to create parve food items which will be served with meat. This means there is a possibility that dairy materials may be mixed in with the parve products to be served with your meat. It's a problem in terms of Kosher standards.
Chabad has created a comprehensive explanation for proper Kosher care in your kitchen. They break down the process of proper surface and utensil care and give you detailed explanations for different items.
Their explanation for ensuring Kosher mixers and blenders is quite simple.
- Small Appliances: An electric mixer, blender or grinder do not require a separate motor in order to be used for meat and dairy. However, one must buy separate attachments if the appliance is to be used for more than one food type (meat, dairy, or pareve). Even when using separate attachments, the machine should be cleaned well on all sides after each use.
You can read more on their website. They cover most kitchen surface/appliance related concerns.