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.
|
Brix reading of Wort |
11 |
||
|
Specific Gravity of Wort |
1.044190027 |
||
|
Gravity Units |
44.19002739 |
||
|
Volume of Wort Collected |
8 |
||
|
Total Gravity Units Collected |
353.5202191 |
||
|
Loss from Boiling – gallons per hour (~15% per hour) |
1.2 |
||
|
Loss from Boiling – gallons per minute |
0.02 |
||
|
Minutes |
Volume |
GU’s |
|
|
Time of Boil |
0 |
8 |
44.190 |
|
15 |
7.7 |
45.912 |
|
|
30 |
7.4 |
47.773 |
|
|
60 Minute Hop Addition |
46 |
7.08 |
49.932 |
|
60 |
6.8 |
51.988 |
|
|
75 |
6.5 |
54.388 |
|
|
90 |
6.2 |
57.019 |
|
|
105 |
5.9 |
59.919 |
|
|
Flame Out |
106 |
5.88 |
60.122 |
Using the GU -> SG -> Brix calculations, we have a OG in the fermenter of 14.76904% Brix
Kettle Shopping
I’ve been shopping kettles recently – actually I’m in the process of a brewery upgrade. I already have a really great kettle for boiling – a 15 gallon stainless steel Megapot. The marketing spiel on the Northern Brewer site describes it like this –
Northern Brewer’s famous Megapots are a homebrewing standard. These are high quality Stainless Steel kettles with a thick three layer bottom – an aluminum layer is sandwiched between two stainless steel layers for superior heat dissipation. This protects against scorching and hot spots when heating a mash or boiling wort. The 15 Gallon pot is 15″ tall and 19″ in diameter. Wall thickness is 1.2 mm.
It’s great. I couldn’t be happier. It’s very wide which is perfect for boiling off volume and the width makes it very stable on the burner (which is an important feature with scalding hot liquids!) It doesn’t retain heat well thought. There is too much exposed surface area. I’m looking for other options for a mashtun/lautertun application.
I looked at the Blichmann BoilerMaker™. They have a great website – lots and lots of sizing and volume information. One of the notes is “the height to diameter ratio is the ideal 1.2 to minimize boil-off and also prevent boil-overs.” Which is an interesting point, but I’m not looking for a boil kettle.
For a mashtun, my Rubbermaid “Gott” coolers have served me well for years. I have come to appreciate the height-width ratio and their ability to retain heat. This started me looking for a kettle that was taller than wide for my mashtun. The main reason I didn’t buy the BoilerMaker™ is this comment from their website… “While the clad bottoms look impressive, they add cost, but no real benefit to the brewer.” I call B.S. on that one – I know for a fact if you are adding direct heat to a kettle without a clad bottom you get hot spots and localized scorching. The tri-clad bottom is important to me.
After kettle geometry, the next important factor is the metal the kettle is made from. I won’t go into a discussion on the suitability of aluminum kettles, just suffice it to say I won’t use one. Call it a personal preference. Stainless steel resists corrosion, is passive and can be cleaned with all the caustics or oxygenated cleaners you want.
Regarding tri-clad (tri-ply) bottoms, it turns out there are several types of wafers used in different kettles – from copper to aluminum to iron core. A quick reference of “thermal conductivity” ratings (measured in Watts per Kelvin Meter) for different metals shows one of the worst heat conductors is Stainless Steel, followed closely by Carbon Steel. Copper, not surprisingly, is the best by far.
Copper: 401 W/m*K
Aluminum: 237 W/m*K
Cast Iron: 80 W/m*K
Carbon steel: 51 W/m*K
Stainless steel: 16 W/m*K
There are some ratings for stainless steel that you will see if you go shopping online. You might see a rating of 304 SS. This refers to the alloys and additives used in the steel – 304 contains 18% chromium and 8% nickel. 316 contain’s 16% chromium, 10% nickel and 2% molybdenum. The “moly” is added to help resist corrosion to chlorides. Similarly, if you see 18/8, the first number is the amount of chromium that is contained in the stainless – 18% chromium, 8% nickel. 18/10 is 18% chromium and 10% nickel. The higher the numbers, the more corrosion resistant the material.
You will also see mm, inch and gauge ratings. These all refer to the thickness. Thinner kettles heat quicker and are easier to move and clean. Thicker kettles maintain heat, distribute heat more evenly and are more durable. It’s a matter of preference and the intended application.
gauge inches mm
16 0.063 1.6002
18 0.050 1.27
20 0.038 0.9652
I’m still looking for the perfect kettle. I think the best I can do in the 50-60qt range with a tri-clad bottom is equal height/width. A word of warning – if you’re buying online, watch out for restocking fees. Vollrath wants a 25% restocking fee! And you have to pay for return shipping. It’s an unexpected hidden hazard of online shopping.
Update – the kettle(s) I settled on are as follows:
Vollrath 47725 Intrigue 53 qt. Stock Pot.
Thanks to its 18-8 stainless steel construction and 1/4″ thick stainless steel clad aluminum base, this Vollrath 47725 Intrigue 53 qt. stock pot heats evenly and can stand up to years of heavy use.
A stock pot’s tall, narrow profile also helps preserve liquids longer and forces them to bubble up through the ingredients in the pot, maximizing flavor transfer. The Vollrath Intrigue stainless steel induction 53 qt. stock pot is NSF Listed, and oven and dishwasher safe. See Companion Items for a compatible cover.
Dimensions:
Inside Diameter: 15 5/8″
Inside Depth: 15 5/8″
Gauge: 16
Vollrath 47778 Intrigue 15 23/32″ Stainless Steel Cover with Loop Handle
This Vollrath 47778 Intrigue 15 23/32″ stainless steel pot / pan cover features a satin finished outside, and a mirror polished interior. A durable welded loop handle is comfortable to grasp and enables easy hanging. NSF Listed. See Companion Items for Intrigue cookware that this cover fits.
Dimensions:
Nominal Diameter: 15 23/32″
Gauge: 16
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.
Epiphany Brewing (tm) 