If this is occuring on random drupelets and more where they are facing the midday/afternoon sun--nothing for it. It is UV (sunlight) damage. Common on certain blackberry varieties also. You might try shadecloth, or even a sheet of plywood if practical.

Berries that mature after the intense heat goes away will likely be normal.

wow -- who knew? that has puzzled me for years as it shows up toward the end of the crop season and thus the warmer days...makes perfect sense -- thanks for the tip

if its UV damage, i would assume late june would be the time where the damage would be most intense... that damage should not relate to temperature, but intensity of light.

perhaps there is a window reflecting the heat in august?

Actually, in Portland June is cloudier on average than May!

I haven't seen UV damage on raspberries in my neighborhood, but on blackberries, it only begins when the blackberries are in the red phase, and this phase doesn't occur until July in this region. Of course many raspberries ripen earlier than this.

I was skeptical of the UV cause, the damage also coincides with stinkbug activity, but after the heat spell (=>90 degrees for 10 days and counting, max 105) this year, I am convinced. An expert at the Caneberry Open House on 8 July near Aurora was also certain of UV as a cause.

The angle of incidence of the UV light may also be critical to cause damage and a somewhat lower sun angle could be more harmful, depending on leaf shading and berry geometry, etc.

UV bleaching pigment would happen when the pigment (DUH) is actually IN THE BERRY. so green june plants might escape trouble- despite the peak of UV. its kinda obvious on second thought!

i suppose there could also be a mechanism that makes the plants more vulnerable to UV damage after intense heat as well. heck, drooping foliage could do it.

thirdly, may with clearer skies than june? count me as suprised!

But raspberries, that were the original complaint, can be red in June.

Yes, actually more clear May days in Portland that June. Average temperature continues to rise in a linear fashion, mostly due to longer daylight, warmer nights when influx of marine air stops temperature drop by 2 A.M. Rainfall drops only slightly, and marine air persists until evening on many June days here.

The whole UV damage thing can be confounding due to the random drupelet damage; one turns white and the adjacent ones remain red/black. Heat is likely a factor as some white damage occurs in very shaded berries. And only on certain varieties. A brief tour of the Aurora caneberry test field after a considerable spell of sunny weather did not show any white damage even though there were many thousands of ripe berries by 8 July.

I don't see this UV problem on my black raspberries; peak harvest this year was 4 July.