Boiling down wort to achieve desired OG impact on hop characteristics

Here's a question that came from performing my first all-grain batch this last Sunday:

Perhaps my mash efficiency was low, or perhaps I had an inaccurate measure of water that I collected for the boil, but when I was finished boiling (per my hops schedule), I found my OG to be a little lower than I'd prefer for the beer I was brewing. Ideally, I would have boiled off more water before I started my hops addition.

My question is: If I continue to boil the wort but have removed the hops, would this additional boiling affect the aroma characteristics from the hops boiled for about a minute or two? Or do the aroma characteristics depend more so on how long the actual hops remain in the wort? (I put my hops in a bag that contains nearly all of them when I boil, so they're easy to remove from the wort.)

Thanks in advanced!

Quick Answer: Continuing to boil wort with the hops removed will drive off volatile (read 'aroma') compounds in the beer. In fact, continuing to boil with hops will drive off these compounds. That's why very little flavor is gained from a 60 minute addition. More bitterness is gained in the later example.

Longer thoughts:

Perhaps my mash efficiency was low, or perhaps I had an inaccurate measure of water that I collected for the boil

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I think you're on track with that. I always had trouble with 'lower than expected' gravity at the end of boil - 'till I got realistic in BeerSmith (the software I use) with the losses and efficiency of my system. Something to consider on future brews.

Even with that, things happen, efficiency fluctuate (to some degree) based on recipe and other variables, but you can always adjust the boil time after your mash. Do a quick calculation at the beginning of the boil: (Pre-boil Gravity)*(Pre-boil volume)=(Post-boil gravity)*(post-boil volume)

You would be solving for post boil volume. Finally, you need to know the hourly rate at which your system evaporates water. Then [(pre-boil volume)-(post-boil volume)]/(hourly boil off rate).

Then just boil that long. If you calculate you need a 75 minute boil, but your hops are scheduled around a 60 minute boil, no worries. You most likely calculated hop additions from the end of the boil, so just add them when you'd planned (i.e. not at the start of boil, but 60 minutes from the end, 20 minutes, 10, etc.)

... I know Promash does this for you, not sure if BeerSmith does. Oh and don't forget an accurate way to measure volume. A calibrated stick works great, and so do sight gauges.

hakedr said:

My question is: If I continue to boil the wort but have removed the hops, would this additional boiling affect the aroma characteristics from the hops boiled for about a minute or two?

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Yes, lengthening the boil will drive off aroma.

Best scenario would be to determine preboil gravity and make adjustments before the hop schedule starts, but that's easier said than done if your low OG is due to boil off rate fluctuations.

hakedr said:

My question is: If I continue to boil the wort but have removed the hops, would this additional boiling affect the aroma characteristics from the hops boiled for about a minute or two? Or do the aroma characteristics depend more so on how long the actual hops remain in the wort? (I put my hops in a bag that contains nearly all of them when I boil, so they're easy to remove from the wort.)

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You would lose most of your aroma from the hops. The aroma would be "boiled off".

Couldn't you add some malt extract to make up those extra points of gravity? That is, if you had some.

That answers my question well. Thanks all. I unfortunately forgot the BTUs of my burner, and this time around I made a 6 gallon batch instead of what I'm used to doing, 5 gallons. I misjudged how much water would boil off. I think I'll figure out the variables as I do it a few more times.

I've considered adding some LME to the fermenting beer. I've seen on other posts that this is acceptable. However, I'm more likely going to just let it go and see how it turns out.

One thing to do before you begin your boil - take a gravity reading, a Boil Gravity. Obviously you will need to correct for temperature. But the amount of sugar you have will not change from this point on.

The gravity will be directly related to the volume. For example, if you have 7.0 gallons of 1042 wort in your pot, you can calculate that at 5.5 gallons your wort will have a gravity of 1053. The sugars do not evaporate, they remain in the pot.

Here is where you as a brewer need to decide your course of action. At 60 minutes of boiling, will you have 5.5 gallons or 6.0 or 6.5? This is why its a good idea to take notes of EVERYTHING. I use my stove and I always have it turned to 8.5 on the dial for consistency reasons. I have calculated my evaporation rate. So if I ever end up with too much wort, I can adjust the amount of hops up or down according to my calculated OG. Or I can boil for some calculated amount of time before I add my 60 minute hops. Or I can add a certain amount of water.

But don't extend your boil once you've begun adding hops, it will change the characteristics of the hops you've added - flavors turn into bitterness, aroma turns into flavor, you lose aroma, etc.