How important is the "float test"

Coming right back - if used - means not enough. Enjoy!

When you say it bounces right back, do you mean the baked bread, or the proofed loaf?

I would expect to see larger bubbles in the starter, but it more than doubles so it sounds all right. I've never used the float test per se, but when I mix water with starter at the start of a new dough, it does seem to float.  Hard to tell since I add a small amount of water first and mix that in first, much like mixing a little corn starch with water first before adding more. Whether the starter will float also depends on whether it gets degassed as you get it out of its container, so I wouldn't get too attached to the idea it needs to float.

Underproofing the shaped loaf could contribute to a tight texture, and using bread flour instead of all purpose flour would make for a more resilient (possibly rubbery) crumb. I don't know your steaming arrangements, but if the crust sets too early it would reduce the final dough volume. If the loaves that seem "rubbery" also have a good open crumb, then I'd try using AP flour.

TomP

i don’t put much stock in the float test, particularly if you are using whole grains. do you use a stone mill or an impact mill? i ask because my stone mill produces noticeably coarser flour than my MIL’s impact mill. with a slightly coarser whole grain making up half of the flour, i can definitely imagine that even a good healthy starter might not pass the float test. my starter is maintained on AP flour, but maybe someone with experience with maintaining theirs with part whole grains will chime in on the float test and the kinds of bubble sizes they see in their starters.

i’m not sure if i’m correctly diagnosing the “rubbery” crumb you’re describing, but i wonder if your bread is slightly underfermented? yet you say you have varied your bulk fermentation time… but have you pushed a loaf far enough to be sure you’ve overproofed it? until i did that, i didn’t realize i had been chronically underproofing my loaves. great oven spring but dense texture. a pic of a recent bake might help.

the only other thing i notice is that your fermentation temperature of 78-80 degrees seems pretty high. is that just your ambient temperature or are you using a proofer? whole grains and high temps make me nervous, things will go real fast ;) if you’re using a proofer it might be interesting to lower that to 72-74 and see if anything changes about your results. of course you’d then need to establish the timing for peak, etc for keeping your starter at a lower temp and maybe that would not be worth the trouble. there are users on here who live in tropical climates and work with temps higher than yours, so i’m not saying it’s necessarily a problem!

hope this helps!

-uvc

If your starter is doubling reliably and rising good bread, I would look at other components to decrease rubbery texture. I second Tom's recommendation to use AP instead of (or to partially replace some) bread flour to see if that solves the problem somewhat.  

Bread flour does give a lot of benefits, among them reliably supporting a long BF with whole grains mixed in and ensuring excellent rise. If you do stick with bread flour, rubbery texture can be reduced by 1) substantially lengthening BF by using less starter or reducing dough temperature, and 2) developing the gluten more (stretch and folds, or whichever method you use).

I don't myself use the float test anymore and I wouldn't be too concerned if your starter looks healthy. You might even find that lowering the hydration of your starter would give you bigger bubbles and help it float! But that might not mean that it has comparatively better rising power in the final dough. 

Lin 

I think it is simply the gluten that imparts the rubbery texture to the bread.

So, the simplest way to get a less rubbery texture would be to use an AP flour with less gluten. Of course, the gluten brings benefits such as dough strength and oven spring that you may see less of if you choose a flour with less gluten.

-Jon

Faering, how often do you feed your starter? Do you mix it until you see signs of gluten formation and  development? Feeding it 1:5, as you do, it should not be too often, right?

My starter is 150% hydration, fed 1:1 every 6-12 hours at 78-80F, and it floats, the entire mass of the starter sits above the water as sturdy foam. One hour after I feed it, I mix it with a fork or handheld blender vigorously until I see it coming together, visible gluten formation and development. Then I let it ferment until mature and feed it again.

My flour is very dry, so my starter's 150% hydration is about equivalent to your starter's  107% hydration.

To me, the starter floating test is important, it indicates that the right balance of yeast and bacteria has been achieved. After refrigeration, my starter eventually floats after a series of three feedings 1:1, i.e. it takes about 24 hours total for it to recover its ability to float after sitting in the fridge for several days or weeks. The first two feedings, it rises, more than doubling each time, but does not float, after the third feeding, it floats.

I rely on the doubling time of the starter and how "fluffy" it is (this is probably the equivalent of the float test).  I only use AP (90%) and dark rye (10%) flour with a hydration of 72%.  It sounds as though there is retained moisture in your bread if it is rubbery.  What temperature do you bake at and for how long?