Low "boil" contributing to low OGs? Other issues?

I recently upgraded my brewkettle from a plain stainless steel 5 gal pot to an 8-gallon polarware. It makes brewing a lot easier, however my stove is having a tougher time getting 6 gallons to a boil than I expected. In fact, unless I leave the lid on for at least 5 minutes (bad idea), I can never reach nor maintain much more than a strong simmer. I didn't think much of this until I also noticed that my switch to a larger pot also correlated with consistently under-shooting my target OG... usually by 5-10 points (I've replaced my hydrometer, so that's not an issue). So my questions...

1) will the inability to maintain a strong boil for extended time reduce the amount of sugars that dissolve in the wort?

2) can extending my "boil" time to 70 or 80 minutes help to mitigate any negative side effects of not coming to a true boil for 60 minutes?

3) is it possible for sugars to coagulate with other solids during the cold break, such that if draining from a spigot they get left behind in the brewkettle?

I'm already taking steps to address these two of these (I just bought an outdoor propane burner for easier boiling, and I plan to strain the wort just to see if that gives me a little bit of an OG bump), but I'm interested if any of you out there have any thoughts on the science behind NOT maintaining a boil and how that may (or may not) affect gravity readings.
Thanks!

saxman1036 said:

I didn't think much of this until I also noticed that my switch to a larger pot also correlated with consistently under-shooting my target OG... usually by 5-10 points (I've replaced my hydrometer, so that's not an issue).

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This is likely b/c you are not boiling off as much water was the recipe expects you to boil off.

1) will the inability to maintain a strong boil for extended time reduce the amount of sugars that dissolve in the wort?

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No. sugars will also be dissolved in non boiling wort. If you stir and there is no sugar at the bottom of the pot (assuming that this is extract brewing) you are fine.

2) can extending my "boil" time to 70 or 80 minutes help to mitigate any negative side effects of not coming to a true boil for 60 minutes?

Click to expand...

No. I'll get to this later

3) is it possible for sugars to coagulate with other solids during the cold break, such that if draining from a spigot they get left behind in the brewkettle?

Click to expand...

No. Sugars don't coagulate with anything. They may bind to amino acids to form Maillard products (How I love the remembering "lard in the mail" to spell this ). But that only happens to a tiny fraction of the sugars.

In boiling we are looking for 5 "-ations" to be done:

- sterilization - you are getting this as long as the wort comes to a boil for a few minutes. It's not sterilization in the truest meaning, but you get the idea.

- volatilization - this is the removal of unwanted flavor compounds, most notably DMS (cooked corn smell). You don't get this with a simmer. At least ~10% evaporation is needed for this on the home brew scale. Big breweries may be able to do this with additional equipment that forces evaporation w/o boiling.

- evaporation - this removes water and increases the gravity of the wort. you are looking for 10-15% of the starting volume

- isomerization - this creates bitterness and you get this even if the wort only simmers

- coagulation - precipitates proteins from the wort. You also get this with a simple simmer but the moving action of a good boil will allow for larger flocks to form.


So yes, use that outdoor burner for your wort boil. But remember more is not always better. Too much heat can also burn you wort. You want 10-15% evaporation per hour.

Kai

Kaiser said:

This is likely b/c you are not boiling off as much water was the recipe expects you to boil off.



No. sugars will also be dissolved in non boiling wort. If you stir and there is no sugar at the bottom of the pot (assuming that this is extract brewing) you are fine.



No. I'll get to this later



No. Sugars don't coagulate with anything. They may bind to amino acids to form Maillard products (How I love the remembering "lard in the mail" to spell this ). But that only happens to a tiny fraction of the sugars.

In boiling we are looking for 5 "-ations" to be done:

- sterilization - you are getting this as long as the wort comes to a boil for a few minutes. It's not sterilization in the truest meaning, but you get the idea.

- volatilization - this is the removal of unwanted flavor compounds, most notably DMS (cooked corn smell). You don't get this with a simmer. At least ~10% evaporation is needed for this on the home brew scale. Big breweries may be able to do this with additional equipment that forces evaporation w/o boiling.

- evaporation - this removes water and increases the gravity of the wort. you are looking for 10-15% of the starting volume

- isomerization - this creates bitterness and you get this even if the wort only simmers

- coagulation - precipitates proteins from the wort. You also get this with a simple simmer but the moving action of a good boil will allow for larger flocks to form.


So yes, use that outdoor burner for your wort boil. But remember more is not always better. Too much heat can also burn you wort. You want 10-15% evaporation per hour.

Kai

Click to expand...

^ what an awesome response! And you have a burner on the way so you're good to go. One thing I do indoors is straddle two burners on my stove to get a better boil but that depends on your stove. I also leave the lid on part way. There is plenty of room for steam/unwanted badness to escape. Especially if I'm boiling more of it off to begin with.

Since this is the science forum, let me comment further on the issue of low boil intensity.

When you boil on a stove top you could boil with the lid partially on as long as you have a way to evaporate a sufficient amount of water at the end of the boil or after. In commercial brewing there systems that pass the boiled hot wort through a “thin film evaporator”. This allows energy efficient boiling with low evaporation while stripping the undesirable volatiles before the wort is cooled. In some cases the wort is merely held at ~100 C for 60 min instead of actually being boiled.

Homebrewers that want to brew on the stove top or want to brew with a heat source that is not capable of sufficient boil-off could build a device that runs a thin film of hot wort over a large surface into a different vessel. The neat thing is that this would also cool the wort somewhat. If the wort temp remains above 60C you should not have to worry about contamination through contact with air. You should also not worry about hot side aeration. Anheuser Bush has a similar system and they don’t have problems with HAS either. The thin film of wort and its heat should provide enough evaporation to strip the undesirable DMS from the wort. You can easily check the evaporation by measuring the gravity before and after the evaporator.

I haven’t tried this myself but it would be an interesting experiment. Finding a suitable evaporator is the challenge. HVAC sheet metal is not a good idea since it will be attacked by the slightly acidic wort. Some zinc is good for the yeast but you may get too much. A stainless steel sheet would be nice, but that’s not cheap.

You’ll need to cool the wort further to pitching temps.

Kai

So, in controlling your evaporation to, say 1-1.5%.. do you think spanning the boil kettle with a large strainer or ss screening material would allow volatiles to burn off while condensing some of the steam and returning back to the boil water..? Is it even worth it? When I brew in the summer, I boil off a lot more than in the winter. So, when I try to figure what my boil off rate is.. it's tougher.. at least for me.

Typically, I leave a lid on the BK with a good crack/opening to allow a bunch of vapor to escape.. but still allow some condensed vapor to return. I may be wrong, but I'm guessing the DMS is like a volitile "gas" that is not necessarily part of the steam evaporating???

I usually do a partial mash with a partial boil + late extracts. Because my electrical induction heater stove is not very strong, I need to cover the pot when I boil 12 L (~ 3 gallons) of wort because it won't boil if I don't. The first 5 - 10 min of boiling needs very careful watching because of risk of spillovers but other than that i don't get any DMS or the like in any of my beers.

So I guess we are fine with covering the pot.

This is why I love HBT. You guys rock.

The propane burner is already on it's way, and it sounds like I shouldn't give up on my brew kettle lid just yet. Although the former may not be as relevant yet because I live in Minnesota... and it's winter.

Thanks!