A tale of two Brewzilla's

[hoppyscotty]

Just thought I'd close out this thread for future prosperity, unfortunately with no hard or firm conclusions, with reporting that recently we did a side by side brew of the two Brewzillas with exactly the same grain bill weighed out to the nearest gram, all grains from the same batch so identical grain crush, the same water (RO that was dosed in one batch with brewing salts before splitting into the two vessels), same mash temps and same mash times, using the same refractometer to measure gravity...absolutely identical process between the two...even plugged into the same electrical supply and still ended up with about 5 point difference in the gravity readings at all stages...post mash, post sparge/preboil and OG.

In fact if anything the vessel that consistently outperforms the other one, and did so here, bunged up with grain as a load of grain got down the central overflow tube and clogged the pump a few times during the mash so if there was a problem with any one of the two vessels you'd thought it would have been that one. So it will remain a mystery...like where your odd socks go on wash day, why wheatabix becomes the hardest substance known to man if you leave it in your bowl to dry and why the amazon delivery guy always arrives just as you're getting into the shower.

Oh well at least the difference between the two vessels is consistent so can compensate for it.

 

[Sadfield]

Given the random nature of your results, I'd be drawn to channeling through the grain bed.

If all measurements were performed in the same way. I still thinking this is the issue, the better performing machine channels less, or flows slower, during mashing. I feel, the intermittently stopped mash being better only confirms this further. Can the flow rate of the two pumps be measured?

 

[Vinylwasp]

As a suggestion - have you checked the mash temperature using an independent thermometer on both setups?

I suspect this may be the right place to look too.
I'd imagine that one way to lower the cost of the Brewzilla is to use less expensive and less accurate temperature probes. If you look at an inkbird 308 for example I'm pretty they use an analog LM35 sensor which has an accuracy +/- 1c. If Brewzilla are using the LM35 too, two systems could conceivably have 2 degrees C variation between which may account for differences in conversion.

 

[hoppyscotty]

Any temp difference between the two was our first throught but not sure of the relationship between mash temp and mash efficiency if there is one, certainly within the narrow range of a few degrees - we only ever mash between 65 and 69 degrees. Of course there is a bit of overshooting according to the Brewzilla display, but when you check with a separate thermoprobe that high temp spike is usually a spurious reading - certainly not representative of the malt temp...this is why I like to run an overflow because I think these spurious temperature spikes are due to hot spots under the malt pipe around the area of the thermoprobe from stagnation of the wort, especially at low recirculation rates as you have with a thick mash, and having some overflow helps to keep the wort in this area moving preventing any deadspots of hot wort. I though about getting a whirlpool nozzle and pulling wort for the recirculation from that via a separate pump so that the wort being pulled through the whirlpool port creates a circular motion of the wort under the malt pipe...but what you actually want is turbulent flow not a nice laminar circular flow...and I cant be bothered modifying the units to that extent.

Maybe I could test this with brew father software to see if grain weight changes with mash temp for the same gravity. It was a double IPA, which is why we were using both vessels to achieve a half decent batch size, so mashed in two vessels then combined the wort and boiled in one.

On channeling...maybe that could be the one area of difference between the two process wise on two counts....we didn't use the top plate in either vessel as we wanted to stir through the mash to try to maximise efficiency, so differences in channeling is a potential difference. Also we added rice hulls to both vessels independently as we were doughing in...a couple of handfuls into each vessel and our handfuls are not calibrated in accordance with any international standard, and one vessel might have received an extra handful so there could be a difference in the amount of rice hulls in each vessel.

....but despite that the results here are consistent with results from all previous brews across the two units. We share the same Brewfather account so use the same recipes across both units with the same equipment profiles and one unit hits the numbers every time without fail, and the other is always around 5 gravity points low every time. Maybe.....

 

[Vinylwasp]

Well I've always thought the sparge is the weak point with these AIO systems because you can't control the sparge rate, which is an important parameter...it just runs through the grain at whatever speed it likes under gravity depending on how thick your mash is. So we have the top plate in place and maintain a quarter to half inch of water on top of the grain to avoid risk of channeling, so just topping up the level of water above the top plate. Having said that with some grain bills the water just runs through straight away the grist is so loose so you can't really build up that quarter to half inch of water above the top plate. I just use a litre jug to keep topping up the level.

The temp of the water is variable. I know not to have sparge water warmer than about 80 degrees, and has to have some temp in it to improve its impact so aim for the mash out temp of 75 degrees but in reality could be cooler than that or a few degrees warmer.

Another couple of ideas:
Doe's your friend stir his mash?
Do you both use the same grain:water ratios?