For me, the taste of summer is a absolutely fresh Eastern WA Bing cherry bought from a popup roadside stand.
You start seeing strawberry stands in early June, but by late June the cherries are ripening and from the end of June to the middle of July it's time to gorge on them until your mouth is stained red from the juice.
Of course Bings aren't the only kind of cherry at those stands; but when I was a kid you rarely saw any other variety. (Sometimes Rainiers.)
http://treefruit.wsu.edu/web-article/cherry-varieties/
[contd]
Nowadays a roadside stand might have Rainier, Chelan, Tieton, Lambert, Index, and (of course) Bing cherries. And all of them have their own unique taste and texture.
And I love all of them. I actually have to watch myself because I will literally eat them until I get sick. (Too many cherries do bad things to your lower digestive tract.)
But, as I said, when I was a kid it was mostly Bings, thus why they are 'the taste of summer' to me.
Go buy some cherries!
