Boil-off rate vs boil intensity & time to get to boil

[cnotts]

In my continued efforts to completely understand my system I've reached a new roadblock I was wondering if any had any experience of.

So - I have been calculating my boil-off rate based on the difference between volumes going into the kettle & into the fermenter (accounting for kettle dead space & hop absorption). However, the difference between my pre-boil OG & my post-boil OG (both temperature adjusted) is pretty different to what my pre-boil & fermenter volumes would imply.

My real questions are;

- Does the time to get to boil affect amount of volume lost without affecting OG, i.e. doesnt concentrate the wort?
- Does the intensity of the boil effect how much of the volume loss contributes to OG increase, or does all volume loss always cause increase in OG?
- Does volume loss during cooling contribute to increased OG?

Appreciate any advice

c

 

[dyqik]

There'll be some evaporation of water before the boil is reached - you can see steam rising before the boil is reached. But that should be pretty minor compared to the boil-off after reaching a full boil.

What you are actually interested in measuring with SG measurements is concentration, not density. To increase concentration, you have to remove water from the solution, or add sugars. Pedantically, volume loss during cooling does technically increase the specific gravity (even of pure water), but what cooling doesn't do is increase the concentration of the wort. Since all your gravity measurements should be done at one temperature, thermal contraction shouldn't show up in your measurements, and cooling does not affect temperature corrected SG. Thermal corrections can be a bit off though, so it's best to actually cool your samples.

Boil off rate should not affect the concentration, only the total amount of water boiled off matters. Although if you boil so hard that you caramelize sugars on the bottom of the kettle (or on the element in an electric system), then that will affect (reduce) the concentration.

Measuring pre-boil (and post-boil) SG accurately can be fairly hard, as wort tends to stratify, with denser wort at the bottom and lighter wort at the top. Stirring a lot helps, as does taking samples while the kettle is at a rolling boil.

 

[kh54s10]

My real questions are;

1)- Does the time to get to boil affect amount of volume lost without affecting OG, i.e. doesnt concentrate the wort?
2)- Does the intensity of the boil effect how much of the volume loss contributes to OG increase, or does all volume loss always cause increase in OG?
3)- Does volume loss during cooling contribute to increased OG?

Appreciate any advice

c

Added numbers to your questions so I could address them.

1) There will be some evaporation while getting to a boil.
2) a strong boil will evaporate more than a weak boil.

Evaporation means less water so a more concentrated wort (higher OG)

3) cooling will not change the gravity. At least measurably. The actual amount of wort is not different. It is just less volume when cool. Like heating a nut to make it expand to loosen it from a bolt. When it cools it goes back to the original size.

 

[Silver_Is_Money]

In my experience a 60 minute rolling boil can and will (when combined with the noticeable effect of cooling post the boil) drop your wort volume by 20%. About 4% of this being from the cooling, leaving a 16% loss in volume due to the boil alone. That extrapolates to ~0.267% loss of volume per minute of boiling.

Martin Bruingard just recently convinced me that a mild boil is more beneficial, and a covered mild boil is even better yet. Much less loss. Much lower Maillard reaction induced wort darkening. And perhaps other benefits as well (hope he will chime in here),

 

[kh54s10]

A 60 minute rolling boil can and will (when combined with the noticeable effect of cooling) drop your wort volume by 20%. About 4% of this being from the cooling, leaving 16% due to the boil alone.

Martin Bruingard just recently convinced me that a mild boil is more beneficial, and a covered mild boil is even better yet. Much less loss.

A covered boil is not a good idea. DMS (Dimethyl Sulfide, I think) in the wort condenses on the top and drips back into the wort. Steam will drive this off.

How much is boiled off is of no real concern as long as it is accounted for. If it is inconsistent it will be hard to account for. So once you find a good boil vigor, stick with that.

 

[Silver_Is_Money]

A covered boil is not a good idea. DMS (Dimethyl Sulfide, I think) in the wort condenses on the top and drips back into the wort. Steam will drive this off.

Martin and Brulosophy have both nixed this concern.

 

[cnotts]

Cool, I guessed as much. So here's my confusion.

Going into the boil I have 30L. Through some combination of boil-off/evaporation/volume shrink from cooling/kettle loss I end up with somewhere a little south of 20L going into my fermenter.

In my last batch I went from a pre boil OG of 1036 to OG of 1045 after using a 75 minute boil, if I'm right, this implies a boil-off rate of something like 2L an hour? So I'm somehow losing ~7L through hop absoprtion & kettle deadspace and I'm sure it's not that high, probably more like ~2/3L. Is my boil-off volume calc completely off - I have been using BrewCipher so I thought this would be feeding in properly?

c

 

[Silver_Is_Money]

Cool, I guessed as much. So here's my confusion.

Going into the boil I have 30L. Through some combination of boil-off/evaporation/volume shrink from cooling/kettle loss I end up with somewhere a little south of 20L going into my fermenter.

In my last batch I went from a pre boil OG of 1036 to OG of 1045 after using a 75 minute boil, if I'm right, this implies a boil-off rate of something like 2L an hour? So I'm somehow losing ~7L through hop absoprtion & kettle deadspace and I'm sure it's not that high, probably more like ~2/3L. Is my boil-off volume calc completely off - I have been using BrewCipher so I thought this would be feeding in properly?

c

I calculate that you are losing about 2.8L to combined trub and hops removal and system dead space, and not 7L.

If 2/3L is due to system deadspace, then you are losing roughly 2.1L to trub and hops removal.

 

[kh54s10]

Martin and Brulosophy have both nixed this concern.

Maybe... But that is 2 against many. Why risk it when it doesn't matter whether you boil off some volume.

 

[Hwk-I-St8]

If you're just looking at the difference between the amount pre-boil to the amount in the fermentor, you're ignoring equipment losses that are not a concentrating factor. For example, if you boil off a gallon, but lose 1.6 quarts to trub loss and wort left in the hoses/pump/chiller etc., then you're going to calculate a higher level and wort concetraition than really occurs.

You need to take pre-boil volume, subtract trub and equipment losses, then take the resulting volume compared to volume into the ferm. That's your actual boil off amount.

 

[oujens]

Maybe... But that is 2 against many. Why risk it when it doesn't matter whether you boil off some volume.

This all goes back to the low oxygen discussion where texts suggest that heat stress is a concern and can have negative impact on your final product if your boil-off exceeds 10%. Reducing your boil vigor and partitally covering the kettle helps to reduce the boil-off and allow DMS to escape. There are more than 2 people reporting no DMS using this method. I have not experienced an issue either. Here is a quick article on the subject:

http://www.********************/uncategorized/low-oxygen-boiling/

Let's not turn this into a debate, but understand there is information and experience out there that indicates we can boil off too much wort and partially covering a kettle should not be a concern for DMS. However, we could not boil-off enough and DMS can be an issue. Partially covering a kettle is really no different than a brewhouse where the kettle is covered and steam escapes through a pipe out the brewery, is it? Hard to compare home brew equipment vs. brewery though.

 

[kh54s10]

This all goes back to the low oxygen discussion where texts suggest that heat stress is a concern and can have negative impact on your final product if your boil-off exceeds 10%. Reducing your boil vigor and partitally covering the kettle helps to reduce the boil-off and allow DMS to escape. There are more than 2 people reporting no DMS using this method. I have not experienced an issue either. Here is a quick article on the subject:

http://www.********************/uncategorized/low-oxygen-boiling/

Let's not turn this into a debate, but understand there is information and experience out there that indicates we can boil off too much wort and partially covering a kettle should not be a concern for DMS. However, we could not boil-off enough and DMS can be an issue. Partially covering a kettle is really no different than a brewhouse where the kettle is covered and steam escapes through a pipe out the brewery, is it? Hard to compare home brew equipment vs. brewery though.

OK. Well there is a big difference between a partially covered pot and a fully covered pot. What I replied to was a "covered" pot.....

 

[oujens]

OK. Well there is a big difference between a partially covered pot and a fully covered pot. What I replied to was a "covered" pot.....

Agree, I was just trying to clarify what Martin had actually suggested. He doesn't recommend a fully covered pot. I should have been more clear myself. I believe he covers the kettle so it makes a crescent moon shape.

 

[Silver_Is_Money]

Brulosophy assuredly left the lid fully on, as can be seen in the brief video at the link below. They boiled at a level that just permitted steam to escape from around the perimeter of the lid, but not sufficiently enough to cause boil over.

http://brulosophy.com/2016/10/31/the-boil-lid-on-vs-lid-off-exbeeriment-results/

 

[doug293cz]

Cool, I guessed as much. So here's my confusion.

Going into the boil I have 30L. Through some combination of boil-off/evaporation/volume shrink from cooling/kettle loss I end up with somewhere a little south of 20L going into my fermenter.

In my last batch I went from a pre boil OG of 1036 to OG of 1045 after using a 75 minute boil, if I'm right, this implies a boil-off rate of something like 2L an hour? So I'm somehow losing ~7L through hop absoprtion & kettle deadspace and I'm sure it's not that high, probably more like ~2/3L. Is my boil-off volume calc completely off - I have been using BrewCipher so I thought this would be feeding in properly?

c

30L @ SG 1.036 corresponds to 24L @ 1.045. That implies a total boil off of 6L, or 6 * 60 / 75 = 4.8 L/hr. 24L post-boil going to 20L in the fermenter implies a total of 4L in trub plus plumbing losses.

Brew on

 

[kh54s10]

I don't do any calculating to determine boil off. You will need to estimate for your first couple of brew days. This is where you would use a calculator. I forget how I determined how much to use in my first full batch.

After a few I found that with small differences due to temperature I need 7 gallons to end up with 5 going into the fermenter. So it is 2 gallons per hour. It is all measurements - no calculations.

 

[cnotts]

Thanks all - I wasn't necessarily worried about losing too much volume (and from the sounds of it the volume saving from leaving the lid on isnt worth the risk [even though it isnt a risk...?]). Was more concerned that even though i was nailing my conversion & lauter efficiency, I was missing on my target OG somehow. I'll just bump up my initial grain bill....