Brew Theory

Easy Gravity Adjustments for All-Grain Brewers

As I’ve said before, I’m a very analog person when it comes to taking notes and making adjustments while brewing. This runs contrary to the rest of my life, which is lived in front of a computer, but brewing is a chance for me to escape to the garage for several hours and read the Sunday paper while I sip a cup of hot coffee.

While my strike water heats, I typically draft up a sheet like this:

Brew Day Sheet

Typically, the only adjustment I need to make is to gravity or volume. I’m not sure if I just don’t brew often enough to have my boiloff rate pegged, or if the humidity really makes such a drastic difference, but the variability seems high with my crappy burner, so I often find myself doing some napkin calculations on whether or not I need to add some DME or boil longer in order to reach the desired specific gravity for a given batch. The calculations are really simple, but perhaps not obvious:

Let’s say for a given recipe, we’re trying to reach a post-boil gravity of 1.060 with a volume of 6 gallons.Our target points is the product of the number of gallons and the desired points:

6 gallons * 60 points per gallon = 360 total points

Now let’s say we ran off 7.5 gallons of 1.046 wort, and compute how many points we yielded:

7.5 gallons * 46 points per gallon = 345 total points

So we were 15 points short overall. We have two options at this point: boil longer, ending up with less than 6 gallons of wort, but reaching the correct gravity, or add some dry malt extract (DME) to make up for the lower-than-expected efficiency and keep our 6 gallon post-boil volume target.

Figuring out the required post-boil volume is simple division:

345 points / 60 points per gallon = 5.75 gallons

This is useful, because boiling off an extra quart might be just fine depending on your system. The DME route is a bit more complicated, but if one pound of DME yields 43 points per gallon (Briess Golden Light) and we need to add 15 total points:

 15 points / 43 points per gallon per pound = 
    0.34 pounds (about 5.5 ounces)

Hopefully this takes some of the mystery out of doing gravity corrections on the fly. There’s surely dozens of smartphone apps to help out with problems like this, but for those of us that enjoy a more unplugged brew day, it’s great to know how to just hammer things out on paper.

Wort Stability Test

I stumbled across an old post over at the Fledgling Brewer blog a couple weeks ago that piqued my interest. Titled, Homebrewer, Heal Thyself: The Wort Stability Test, it introduced a simple sanitation test that I’d actually done in the past, but hadn’t considered as being a thing with a name to itself.

A couple years ago, I fought with some off-flavors after bottling. In trying to find the source of the off-flavors, I bottled some wort from various stages of the cool side and tested how they tasted 4 or 5 days later. All of them were fine, until I got to the bottling end of things, and through process of elimination, I eventually narrowed things down to the bottling bucket or spigot (I replaced both).

As it happens, a simpler version of this test is discussed on the commercial side of the Wyeast Labs site:

It is important that a brewer regularly check the stability of the wort produced. A very simple and effective method is a wort stability test. This test can be performed by any brewery with or without a lab. The wort stability test consists of aseptically pulling a wort sample (post heat-exchanger) into a sterile sample container and holding that sample for 3 days in a warm area. If the sample remains clear and no CO2 is formed, the wort is stable. If the wort clouds up, CO2 is formed, a film develops on the surface, or off aromas are detected, then you know that you have a problem.

Wort Stability Sample This is such a simple sanity check, it seems worthwhile to do at least once or twice a year, so I pulled about 8 ounces of wort on it’s way to the fermenter into a sanitized beer bottle this Sunday when I was brewing what I’m calling the Freezer Burner APA.

This was especially timely because I’m planning on harvesting and rinsing the yeast from this batch of beer to repitch into an IPA I’m making in a few weeks, so I’d like to make sure it’s reasonably free from bacteria and other spoilers.

You can see the sample isn’t brilliantly clear, but it tasted and smelled exactly like the fresh wort going to the fermenter 3 days prior, and I believe some of the cloudiness was due to my less-than-careful pouring from the bottle into the sample jar.

I’ve never repitched yeast before, but knowing the initial batch had a nice healthy starter, controller fermentation temperatures, and the wort was essentially as sanitary as we can hope for going into the fermenter gives me a little extra piece of mind that I won’t be ruining 10 gallons of wort in a couple weeks by pitching less than clean yeast slurry.


Brewhouse Efficiency Primer

Having about 15 all-grain batches under my belt, I have a pretty solid grasp of my equipment and I’ve done well at hitting my brew-day numbers with one nagging exception: original gravity.

In all-grain brewing, OG is a product of brewhouse efficiency, a simple calculation using the amount and type of grains and volume of wort produced. It essentially describes how well brewers are able to extract sugars from a grain bill, measured against the theoretical maximum gravity that might be obtained from said grains.  A oft-used rule used by homebrewers is to aim for 75% if you’re unsure what to expect. As an example, if we apply that to a grain bill like the following…

  • 8# Marris Otter
  • 1# Crystal 40L
  • 8oz Carapils
…we can expect our OG to be 1.053 for 5 gallons of wort. If your pre-boil gravity is 6.5 gallons, you should expect that wort to be 1.041 before it’s boiled down. So having glossed over the math entirely, the point I’m really getting at is this:

Brewer’s Axiom #17: In order to craft recipes and make an informed expectation about the kind of beer a given grain bill will produce, a brewer must know his expected brewhouse efficiency

I made that up just now, but that doesn’t make it any less true.

At the homebrew scale, grain crush is a primary driving factor in one’s brewhouse efficiency, and it’s the first thing to look at if you’re getting consistently low or sporadic numbers (people mess with the mill gap at homebrew shops constantly).  I started to realize just how big of a problem this has been for me while cleaning up from my New Years Day brew, which was Northern Brewer’s Extra Pale Ale kit. They list an expected OG of 1.045, which is about 70% efficiency based on a final volume of 5 gallons and the grain bill they list. I hit that volume dead on, but my gravity was a paltry 1.038, or 61% efficiency. The beer is drinkable, but only just. It tastes overly sweet  given the low alcohol level in the final beer (3.68% vs 4.59% expected). I dubbed it the Extra Mild Ale.

Just before mash-in, I looked at the crushed grains and thought, “That is waaay too course”, but there was little I could do at that point but brew, so brew I did. I thought this was an isolated incident, but after the brew was in the fermenter, I pulled out my brew sheets and found my efficiency has ranged anywhere from 59% to 78%, which is too wide a gap to base any recipes on. It’d be better to be be consistently at 60% than all over the board, so I set about to solving the issue the best way that I could: buying a mill.

I wanted something that would last me, made by a company that would stand behind their product if it didn’t. I settled on the mill that Rebel Brewer is having manufactured under their name. It arrived a couple weeks ago, and I was able to use it for the latest round of my India Rye Ale.

I’ll have a full writeup coming this week covering the unboxing and crush in-depth, along with some numbers to go along with it, but my initial impressions are nothing but good. This thing is built to last, and I’m excited to put it through it’s paces this spring with some more batches.

Stay tuned!

Rebel Mill