Category Archive

I recently sent out an email the KROC mailing group regarding “preboil gravities” that are computed in ProMash, which is a good piece of software with lots of features.  Unfortunately it is getting dated (the website shows 2003 as the last update) and I have never heard of an ingredient update.

There was a lot of good advice regarding checking the grain crush, mixing the wort in the kettle, cooling the wort sample, taking hydrometer readings among other recommendations.  I won’t repeat the entire discussion thread here, please ensure you are signed up to get KROC emails if you missed it.  I want to actually introduce a means to predict what the gravity of the wort you will have in your fermenter based on what you start with.  It might get geeky, and as our friends in the UK say – there might be some maths involved.

First off – what do brewers mean when the talk about gravity?  The acceleration of objects on the surface of the earth towards the center at 32 feet per second squared?  No.  We are discussing specific gravity.

Specific gravity is the ratio of the density of a substance to the density (mass of the same unit volume) of a reference substance.  Said another way, SG is the ratio of the density of wort to the density of water.

Specific gravity, as it is a ratio of densities, is a dimensionless quantity. Specific gravity varies with temperature and pressure; reference and sample must be compared at the same temperature and pressure, or corrected to a standard reference temperature and pressure.

Specific gravity can be measured using a hydrometer.  Operation of the hydrometer is based on Archimedes’ principle that a solid suspended in a fluid will be buoyed up by a force equal to the weight of the fluid displaced by the submerged part of the suspended solid. Thus, the lower the density of the substance, the farther the hydrometer will sink.

The “Plato scale” is an empirically derived hydrometer scale to measure density of beer wort in terms of percentage of extract by weight. It was developed in 1843 by Bohemian scientist Karl Balling as well as Simon Ack, and improved by German Fritz Plato. The scale expresses the density as the percentage of sucrose by weight (grams of sugar per 100 grams of wort), so a wort measured at 12° Plato has the same density as a water−sucrose solution containing 12% sucrose by weight, denoted as 12% Brix. For the brewer, it has an advantage over specific gravity in that it expresses the measurement in terms of the amount of fermentable materials. Degrees Plato are more popular in central European brewing, and occasionally feature in beer names.

Given that background information, the questions remain – given a pre-boil sample of wort, can I predict what my Original Gravity will be in the fermenter?  What is the 60 minute mark for hop additions?  Will I need to add water or boil longer?  These are knowable details, but we need to take a few measurements first.

What is the volume of wort collected in the kettle?

What is the “density” – or the percentage of “sucrose” by weight (% Brix)?

A couple of points to consider:

• the collected wort will be hot, usually around 165F, so the density will be lower.

• the wort in the fermenter will be cool, usually around 68F, so the density will be higher.

• the boil will condense the wort by boiling off the water (somewhat obvious.)

Useful formulas:

SG -> Brix Equation:

    Brix = (((182.4601 * SG -775.6821) * SG +1262.7794) * SG -669.5622)

(Source: http://en.wikipedia.org/wiki/Brix)

Brix -> SG Equation:

    SG = (Brix / (258.6-((Brix / 258.2)*227.1))) + 1

(Source: Brew Your Own Magazine)   

Gravity Units

Ray Daniels introduces the concept of Gravity units.  They’re pretty easy to use, so I’ll follow his lead.  If you have a hydrometer, it’s easy – the gravity units are the last two digits of the SG – e.g. 1.050 is 50 GU, or mathematically GU = (SG – 1) * 1000.  If you are using a Brix refractometer, plug the Brix to SG equation into a spreadsheet or just look for a calculator online that will do the conversion, then use the GU formula (hint: it’s the last two digits).

So lets say a brewer named Rick decides to brew a nice ESB one day.  He reads a recipe in the Brewing Basic Styles, plugs the numbers into ProMash, buys his grains and gets set for a brew day.  Because I’m “batch sparging” (which Bob Z rightly points out is a misnomer) I have been adding a couple extra pounds of base malt to grind.  I ended up with some wild numbers – about 8 gallons of wort collected for a 5 gallon batch and measurement of about 11 Brix.

Assuming a boil loss of 15%, you will lose 1.2 gallons per hour, or 0.02 gallons per minute.  Using  (GU*original volume)/(original volume – time in minutes * loss per minute) you can estimate the GU’s at any point in time.  Obviously these measurements would have to be tested for accuracy!

Sparge yield of 8 gallons (use a measuring stick customized for your kettle if you don’t have a liquid level indicator).  Preboil density measured at 11 Brix.  Target ~5.5g-6.0g at 1.060.

Using the GU -> SG -> Brix calculations, we have a OG in the fermenter of 14.76904% Brix

Well, perhaps throwing your stir-plate away is a bit drastic. Recycle it in an earth friendly manner. No, keep it – you might still need it someday.

I’m moving to a Lab Mixer for yeast propagation.

Read the article here.

I’ve had a March 809 pump for some time now. I haven’t been using it because it cavitates when pumping hot water. During a KROC homebrew club meeting I over heard a guy talking about mounting his pump in a tool box. He showed me a few pictures and viola – here I am with a similar setup.

The nice features of this arrangement are – I added a 30A 2 pole on/off switch (which is upside down at the moment), a nice junction box for the wiring, a 6″ pine board for mounting the motor. I mounted the pump head before mounting the motor so I was only able to get one bolt to secure the motor mounting – if you attempt this, make sure you drill your motor mount holes in advance. When attaching the pump head to the motor I needed to buy longer 8/32 machine screws – 1/2″ worked well. To locate the spot to drill for the screws I followed another websites recommendation to put the screws in without the pump head, then put toothpaste on the screw heads and lined it up. The walls of the tool box were angled, which is not ideal, so I did have to expand the size of the holes to get be able to line them up.

Lot’s of close work getting everything mounted in a small box – but I think the results were worth it. It adds a large amount of “cool factor” to the pump and should make it much more usable.

Apparently if you haven’t been living on the west coast you are probably missing out on a popular regional food – smoked tri-tip! A friend sent a bunch of us some of his custom dry rub and challenged us to come up with a photo journal – this was my submission (I came in second place on this one).

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A beautiful hymn sung during the mass for the feast of the Epiphany today – http://www.youtube.com/watch?v=mEkdr62eVMY

This was one of my earlier brewdays. I was experimenting steam injection to do a step mash and using a paint mixer to oxygenate the wort. I was also using a light bulb in my fermentation chest freezer and a bucket. When I moved to glass carboys I switched to a fermwrap to heat the carboy. Reposted from BigFoamyHead.com.

Pics! 🙂

mashing in

Infusion mash

Steam Injection Step Mash

God Bless Freight and Harbor! Cheap steam cleaner.

Iodine Tincture test to check for mash conversion

Three tier gravity based sparge

Ooooh Wooow - laser drilled sparge arm!

Collecting sweet wort

Time to boil

straining out whole hops - they did their job.

Aeration with power tools and a paint mixer!

In the fermenter with a blow-off tube in sanitizer

It’s been too long since I’ve updated my blog. This is a good one though – Boulder Beer had it’s second “rave” – this one during the day and featuring mostly Colorado beers.

Highlights from the Beer Score Card
Avery Brewing Company – Moloch (fantastic strong malty beer)
Blue Moon Brewing Company – Peanut Butter Ale (downright yummy!!)
Coopersmith Brewing – Chai Stout (this is always excellent)
Dillon Dam Brewery – Oktoberfest and Dunkelweiss
Estes Park Brewery – 9 hop pale ale! 🙂
Gordon Biersch Brewery – Blonde Bock
Great Divide Brewing – Year old Old Ruffian Barleywine (need I say more?)
Left Hand Brewing – St Vrain Trippel
Mountain Sun Brewing – Superkind 🙂
New Belgium Brewing Company – Tart Lychee (awesome sour beer)
ODell Brewing Company – Bourbon Stout (nice bourbon character!)
Oskar Blues – Barrel Aged Pilsner (another awesome beer!)
Pumphouse Brewery – Cherry Bomb Saison (YUM!!)
Sam Adams – Belgian Red (meh)
Trinity Brewing Company – Farmhouse Provisional (don’t remember it)

Not on the score card, but I enjoyed numerous Sierra Nevada Big Foot Barleywines! Fresh, strong and hoppy!
What was particularly cool about this event is that Boulder beer is celebrating 30 years so they had the breweries lined up by years in business.

They also opened up the brewery so there was plenty of room and snacks.

I am glad I took the bus to this event and got there a little late – this was not an event to drive away from. I’m still mad at my designated driver for bailing out on me, but it’s good to know how to use public transportation if needs be.