Starter suddenly stiffened

[ARenko]

I'm 7 days into activating a starter.  After initial activation I've been feeding every 12 hours 100g flour/ 100g water.  The last feeding the starter stiffened up quite a bit.  I'm pretty sure I measured everything right, and I'm doing two batches (just in case I screwed up one) and both starters stiffened up.  I would've had to screw up twice since I discard/ feed one before the other.  The only difference is I switched from Kroger brand unbleached AP flour to King Arthur unbleached AP flour.  Could this make such a difference? 

[HansB]

The change of flour should not have made a difference. Probably mis measured if there were no other changes.

[ARenko]

Yeah I wouldn't think the flour would make a difference, and maybe I mismeasured, but I would've had to do it twice and in the same way since I deal with one starter completely then the other.  The scale is tared several times during the process.  Yet both batches behaved the same.

[ARenko]

Remembered I had a bit of the Kroger AP in a plastic bag that didn't fit in my container, so did a 100% hydration of each flour as a test (separate from the starter).  The KAAP was noticeably stiffer.  With the Kroger flour my starter would rise and fall.  With the KAAP it rises, but doesn't fall (or barely falls).

[The Dough Doctor]

A number of years ago we did a study on similarity of flour by type from different manufacturers, we found that there was a very high level of similarity between bread, and H&R type flours. The so called "high gluten" flours were somewhat variable with some having a protein content as low as 12% while others were in the 13 to 14+% range. With AP type flours we found even greater variances as some AP flours were made from soft wheat varieties and others were made from hard what varieties with protein content all over the board from a low of 9% to a high of nearly 12%, and remember that there is a significant difference in the gluten characteristics between flours made using hard and soft wheat. Based on this study we developed the recommendation to be very cautious when changing brands of AP flour.
Tom Lehmann/The Dough Doctor

[ARenko]

A number of years ago we did a study on similarity of flour by type from different manufacturers, we found that there was a very high level of similarity between bread, and H&R type flours. The so called "high gluten" flours were somewhat variable with some having a protein content as low as 12% while others were in the 13 to 14+% range. With AP type flours we found even greater variances as some AP flours were made from soft wheat varieties and others were made from hard what varieties with protein content all over the board from a low of 9% to a high of nearly 12%, and remember that there is a significant difference in the gluten characteristics between flours made using hard and soft wheat. Based on this study we developed the recommendation to be very cautious when changing brands of AP flour.
Tom Lehmann/The Dough Doctor

Thanks Tom.  Changing flour was driven by the current shortage on the store shelves (everyone's a baker now).  I'd prefer the less stiff starter.  I assume there wouldn't be an issue for me to switch back at some point.  My starter seems to be pretty active now so I don't think there was any negative effect of the change other than it stiffened my starter.