If I end up with too low of a gravity can I just boil longer?

So I've noticed in Beersmith when I'm doing my small batch BIAB beers it always is telling me to use more water than when I use a strike water calculator (usually use the on the one on BIAB calculator.com) and tells me to make the water substantially hotter. When I use the calculator I hit my mash temp spot on but in the end I end up with a lot less beer in the end. If I use Beersmith's water volume and end up with more wort than expected and/or too low Preboil gravity, can I always just boil longer than an hour to get to the correct OG (I know I still end up with less). I just want to know that if my preboil gravity is too low (which it is half the time) it's easily corrected by boiling a little longer. I may have a follow up question based on the answers I get here. Thanks!

 

Yes, you can control OG by altering the boiling time. The one thing you need to watch for is hop exposure time. A 60 minute addition will become 75 if you extend the boil for 15 minutes. That's not a big deal, as additional bittering from an early addition is probably not perceptible. But a 5 minute addition will become 20, which can alter bitterness and flavor a lot. That's the only real "gotcha" with the technique.

 

I just keep DME on hand and add a little if I miss my numbers.

 

Aha! I knew there was something I wasn't thinking of. So maybe taking a refractometer reading before adding my 15/5 minute additions would be a good idea.

 

I've never done that yet. So if my preboil gravity is low I can just add some DME instead of boiling longer? I'm assuming there's a calculator where you can put in preboil gravity what you want it to be and it gives you how much DME to add? When you do it that way I guess you just have to hope you added the right amount because you can't really add it dry and take another reading before boiling, correct?

 

One thing you can try is to go with a normal bittering addition, say 60 minutes. Halfway through the boil - 30 minutes - take a gravity sample. Make sure it's really well mixed and contains wort from the top, middle, and bottom of the kettle. It will be more or less 50% of the way to OG. You can then judge if you want to extend the boil time, and you can adjust your later hop additions to compensate for the true end-of-boil.

For example, let's say you start with 1.040 pre-boil on the way to 1.052 OG. You'd expect the halfway point to be 1.046.

This necessitates an accurate pre-boil gravity to work (again, really well mixed). That's actually harder than it seems, and can easily result in being misled halfway through. I take my pre-boil sample just near the onset of the boil, and use a ladle to both stir and scoop liquid from different strata of the kettle.

 

I keep records on all my brews and many things are very consistent. For example, the water absorbed by the grains in the mash tun always ends up being 0.12-0.13 gal/lb, and my boil off rate is always right around 2gal/hr. With this info it's pretty easy to make a quite accurate first guess at how much water to add and how long to boil to get a certain volume with a certain OG.

Personally, I'd much prefer to plan for a longer boil than to add DME. I'd rather my gravity miss the Beersmith prediction by a few ticks than to tamper with the recipe by adding additional fermentables.

 

Very interesting point about making sure it contains wort from top,middle and bottom of kettle. I've never even done that when taking my preboil gravity. How would you do that? A turkey baster and taking a little at different levels? Then shake it up , let it cool for a few seconds and use that? I wonder if I am consistently getting preboil gravity so low because I'm just taking a spoonful from the top and using that. I mean it is super low all the time then I do some squeezing and dunking until it's higher. Maybe it's starting off ok but I'm just not getting a good sample. Now I'm itching to brew this Sunday

 

I use a stainless ladle. And I wait til the wort is all in the kettle, and the hot break is forming. I stir in circles, but also lift it up and down, then just scoop a bit from bottom, middle and top. Pre-boil gravity is notoriously difficult to read accurately due to stratification of sugars at this stage (they mix better as boiling progresses).

I also use a refractometer which makes it easier, but the same technique will work with a hydrometer. Just cool down the wort first, obviously!

 

I have had a little too much volume a few times after sparging and I have gone with extra boiling before adding hops.

 

Alternatively, you could also just wait for the wort to boil a minute or two. As long as you haven't just added any extracts, the convection in the boil should be entirely sufficient to homogenize the mixture. Once you take that reading, you can decide whether you are ready to add your 60 minute hops or need to boil down a bit first.

 

Keep in mind that this will make your hop utilization change. You have left wort in the end with the same amount of hops..i.e. your ibu's will increase.

It is the same concept as 1 once of hops in a 5 gallon batch lends 20 ibu's..the same amount in 10 gallons will lend 10 ibu's

 

So you take the preboil gravity after the wort is heated up and the hot break is forming? I usually take it before I even put it on the burner. Never heard to do otherwise. Thanks for the info. That will eliminate me squeezing and dunking the bag until I got to the desired preboil gravity because, once the hot break is forming, that won't be an option any more. At the same time, that reiterates my thought that my preboil gravities may have been ok all along and my squeezing/dunking was going overboard (since most of my OGs are way too high).

 

Yes

 

Just one thought on what might be going on. For BIAB, BeerSmith estimates the absorption loss to grains too high. My loss is much closer to .1 gal/10 lbs so I just reduce the amount of water BeerSmith tells me to use. For a 3 gal batch, I just add a touch more water than I want for pre-boil volume and have been happy with the results.