Like I said, I'm doing a lot of taste-testing this week, and so I have tasting protocols on my mind.
People often ask me what coffee tasters do to cleanse their palates. My answer is: usually, not much!
Coffee (especially non-espresso coffee) is heavily water-based... about 98.7% water in most cases. When comparing just a handful of coffees, all you need to cleanse yourself of the last coffee is.... the next coffee. However, over time and many samples, you will develop some build-up. There's nothing wrong with cleansing, especially if you find it helps you.
The best cleanser in life, in all circumstances, of course is water. When I do tasting, no matter if it's cupping, brewed coffee, espresso, or whatever, I always have lots of fresh water on hand. I like the water to be not too cold, as having really cold water can provide a shock to your senses. Also, it's best to use the same water source as is being used to brew your coffee. That means if your brew-station has a water filtration system, it's best to be drinking water that is similarly filtered. But, really, any old water will do.
Swishing water around in your mouth and spitting is a good practice. It's also a good idea to drink plenty of water if you are going to taste a lot of coffees. Even if you are spitting most of your coffee samples, you are going to absorb a lot of caffeine through your mouth. Drinking plenty of water helps ensure your body will be able to handle it.
When I have a lot of coffee to sample, I will use crackers to cleanse my palate. Choose something neutral, like soda crackers or table water crackers. Make sure to rinse with water after to get all the cracker residue out of your mouth.
Pears and apples are also a common way to refresh yourself between sets. I strongly recommend you stay away from this kind of palate cleanser when you are in the middle of tasting. But if you have several sessions planned, having a few slices of a sweet apple can scrub your tongue a little and refresh you. Again, finish with water.
Finally, espresso is a special case because of all the oils involved. I like to serve people sparkling water when hosting an espresso tasting. Stay away from flavored waters. A good, relatively neutral water like Perrier should do the trick. Swish and spit, and swish and drink. Have some still water on hand, too, as always!