Robobrew/Brewzilla Discussion

[doug293cz]

I totally disagree. I have thought about this, and experimented with the settings for a long time to see a significant difference.

What you failed to realize is that there is a constant pool of wort sitting directly over the heating element. This pool quickly gets heated to the target temperature and turns the heater off, until it eventually cools down again. With the pump on full (i.e. 100% setting), the cooler wort is all pulled directly from the mash to the outlet and then recirculated. This cooler wort barely has time to spread out over the heating element and heat up, so it remains realitively cooler. So eventually the wort cools down while the wort pooled over the heating element stays at a higher temperature, closer to the target temperature. When the pump goes on intermitenly, the cooler wort stays over the heating element for a short period of time, during which it can spread out and heat. The the pump swtiches on again, pulls this heated wort through the outlet,and reciculates it back over the wort.

This is the exact reason why they developed the diverter plate. Instead of the wort from the mash getting sucked directly to the outlet in a focused line of transmission, the plate allows the wort to spread out over the outside of the plate and then under, which forces it over directly the entire heating surface before it exits through the outlet.

If you try it you will definitely notice the difference.

Have you ever taken a course that involved thermodynamics? You seem to be confused by the point that I made about more local heating with less flow. The amount of heat transferred to the total volume of wort is the same, for the same power input to the element, regardless of flow. With less flow, you get more local temperature rise, but the same amount of heat transferred to the wort.

Brew on

 

[mashdar]

There might be some non-linear effects of modulated vs constant volume, regarding the dynamics of the flow, but you'd probably need a 5x or higher peak for it to be significant.

More likely is mistaking a probe temperature for an average mass temperature.

 

[Bottoms_Up]

I took Engineering in University so I know all about thermodynamics. My point all along was about heat exchange involving localized flow which you seem unclear about, and which causes significant fluctuations of temperature and extended delays in stabilizing. This is why you stir when you chill your wort and why you stir your mash. The localized temperatures can vary considerably depending on the flow and localized heat/cooling.

The temperature probe in the Brewzilla is situated around the outside circumference. The outlow/drain is in the centre. The pump draws the wort directly to the outlet in the centre and NOT to the probe. Thus the localized wort adjacent to the probe can be many degrees higher than that coming from the mash. If it is still hot enough around the probe, and there is not much localized flow, the heat won't turn on for some time. That is why, when you calibrate the temperature sensor, you measure the temperature immediately adjacent to the probe, and not near the centre. Whenever the heater turns on, it first heats the wort directly above the heater element, which is near the probe. It thus takes a long time for the heat to spread throughout the Brewzilla and stabilize. You should know that.

If you still disagree, contact Kegland and ask them why they bothered designing a plate diverter after many complaints involving this very issue I've been trying to explain (i.e. the sigificant difference between the probe temperature and the mash temperature, measured by a different means, such as the EAPT probe). Over time the temperature may become closer, but during that time there can be significant swings in temperature, so that during the more critical times of the mash (i.e. the first 15-20 minutes) the mash temperature may be significantly different than your desired mash temperature).

There's a long discussion about this on the site somewhere.

 

[Yooper]

I took Engineering in University so I know all about thermodynamics. My point all along was about heat exchange involving localized flow which you seem unclear about, and which causes significant fluctuations of temperature and extended delays in stabilizing. This is why you stir when you chill your wort and why you stir your mash. The localized temperatures can vary considerably depending on the flow and localized heat/cooling.

The temperature probe in the Brewzilla is situated around the outside circumference. The outlow/drain is in the centre. The pump draws the wort directly to the outlet in the centre and NOT to the probe. Thus the localized wort adjacent to the probe can be many degrees higher than that coming from the mash. If it is still hot enough around the probe, and there is not much localized flow, the heat won't turn on for some time. That is why, when you calibrate the temperature sensor, you measure the temperature immediately adjacent to the probe, and not near the centre. Whenever the heater turns on, it first heats the wort directly above the heater element, which is near the probe. It thus takes a long time for the heat to spread throughout the Brewzilla and stabilize. You should know that.

If you still disagree, contact Kegland and ask them why they bothered designing a plate diverter after many complaints involving this very issue I've been trying to explain (i.e. the sigificant difference between the probe temperature and the mash temperature, measured by a different means, such as the EAPT probe). Over time the temperature may become closer, but during that time there can be significant swings in temperature, so that during the more critical times of the mash (i.e. the first 15-20 minutes) the mash temperature may be significantly different than your desired mash temperature).

There's a long discussion about this on the site somewhere.

Right. That's why I bought the optional HED (Heat Exchanger Dish) which should be standard with it.

The center hole is the issue. Even with the HED, using a calibrated RAPT thermometer at the top, the temperature was much higher at the bottom than the middle of the mash, doing constant recirculation. It was a big difference, and may account for my lower attenuation in my pilsner. My desired mash temp was 147. The PID was kicking the heater on, up into the 160s, while the RAPT was reading 146. Constant recirculation with the valve about 1/3 open, stirring, etc- and still the disparity. Even using the 220V, it took a long time for step mashing.

It's ok, and I plan on continuing to use the Brewzilla as it is still more convenient in a lot of ways than my big old 3 vessel. But there are definitely limitations!

 

[Bottoms_Up]

Right. That's why I bought the optional HED (Heat Exchanger Dish) which should be standard with it.

The center hole is the issue. Even with the HED, using a calibrated RAPT thermometer at the top, the temperature was much higher at the bottom than the middle of the mash, doing constant recirculation. It was a big difference, and may account for my lower attenuation in my pilsner. My desired mash temp was 147. The PID was kicking the heater on, up into the 160s, while the RAPT was reading 146. Constant recirculation with the valve about 1/3 open, stirring, etc- and still the disparity. Even using the 220V, it took a long time for step mashing.

It's ok, and I plan on continuing to use the Brewzilla as it is still more convenient in a lot of ways than my big old 3 vessel. But there are definitely limitations!

Thanks for the verification. This is the exact issue I've been trying to explain. I agree that all future Brewzillas should include the heat exchanger dish (diverter) as a standard part of the design. It is almost useless without it.

However, I did try to explain one way in which the Brewzilla could be used, if one doesn't have the HED. And that is by setting the pump to 45% or even less. This allows the wort to momentarily pool along the bottom of the Brewzilla, over the heating elements, during the period the pump is momentarily halted, thereby giving it more chance to heat before it gets recirculated back to the mash. If the pump is on continuously, the wort from the mash gets sucked into the centre hole directly, so that it has little chance of spreading over the heating element and heating. As a result, there will be great fluctuations of temperature and variations between the probe temperature and the mash temperature before the system finally reaches any state of equilibrium, which could take well over 15-20 minutes, which is the critical time for conversion.

There are numerous factors involved in reaching an acceptable state of equilibrium, apart from just simple thermodynamics:

- the location of the temperature sensor
- the location of the drain
- the thickness of the mash (water to grain ratio)
- the crush of the grain
- the types of grains and adjuncts used
- the ambient temperature in which the Brewzilla is located
- whether or not the Brewzilla is insulated
- the strength of the pump
- the amount that the recirculating valve is opened
- the cylcing duration of the pump
- the intensity of heat (% setting)
- whether or not a RAPT probe is inserted in the mash, and is set as the main sensor
- whether or not a HED is used
- whether the PID option is used

All these affect the length of time in which an acceptable stable temperature is reached. The interplay of all these factors involves a sort of art, based on a lot of trial and error, as I have found.