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| Topping off & Brewing with Oats |
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Dear Mr. Wizard:
I have seen a lot of recipes in your magazine described as "5 gallons." How then, if a collection of 5.75 gallons of wort and a 90-minute boil are called for, can you end up with 5 gallons? As a rule, I boil 7 gallons of wort for 90 minutes and rarely end up with 5 gallons in the primary. In fact, my last effort netted me 4 gallons of wort and probably a gallon of trub. Is topping off the answer?
Rick Rocheleauvia
e-mail
Mr. Wizard replies: This is a good question. All brewing recipes give a volume of wort to collect before boiling as a guideline. But the volume that really matters is the wort volume after boiling. Wort volume is very important because it directly affects the concentration of everything dissolved in the wort. Specific gravity, bitterness and color are all affected by changes in volume.
All brew kettles are different with respect to their evaporation rate during boiling. Evaporation rate varies with the shape of the kettle, the material of construction (stainless, aluminum, copper) the thickness of the material and the heat source.
Most commercial brewers try to evaporate about eight percent of the wort volume during the boil. In a large brewery this figure is critical, because excessive evaporation wastes energy, is expensive, and does not add anything to beer quality. It sounds like you have a pretty aggressive boil! I would take a vigorous boil over a wimpy boil any day.
Now for the practical advice. I try to nail my wort gravity coming out of the kettle. The easiest way that I've found to hit a target gravity is to measure the specific gravity after the boil and add hot water to the wort to adjust the gravity. The wort gravity must be a little higher than the target gravity for this method to work. If the wort volume after adjustment is much different than the target volume for the recipe, the bitterness may be higher or lower than projected, but you can't worry about nailing every parameter. In most cases the adjusted wort volume is close enough to the target batch size and bitterness is not significantly changed.
To apply this technique you must:
1. accurately measure the volume of your wort.
2. calculate how much extract is dissolved in the wort.
3. calculate the adjusted wort volume.
4. add hot water to the brew kettle.
The easiest way to measure wort volume in a kettle is by using a calibrated dipstick made of hardwood. I like to cut notches in the stick at convenient intervals, for example every 250 ml (metric is much easier to use in the brewing calculations).
Here's an example: Suppose you have a recipe that should yield 5 gallons (18.9 liters) of 1.048 (12° Plato) wort and you determine that you actually have 4.3 gallons (16.3 liters) of 1.055 (13.5° Plato) after the boil.
Step One:
How much extract is present?Kg extract present = (liters of wort) x (specific gravity) x (°Plato) = (16.3) x (1.055) x (0.135) = 2.32 kg
Step Two:
What is the adjusted wort volume?Adjusted volume =(kg extract present) ÷ {(target SG) x (target °Plato)} = (2.32) ÷ {(1.048) x (0.12)} = 18.45 liters
After crunching a few numbers you can simply top your kettle up to 18.45 liters by adding 2.15 liters of boiled water. There are a few notable details in the calculation shown above. Plato must be expressed in decimal form because degrees Plato is a weight/weight percentage (12° Plato means the wort contains 12 grams of solids per 100 grams of wort).
A rough conversion between degrees Plato and specific gravity can be made by dividing the specific gravity number behind the decimal (often called points of gravity) by four. A specific gravity of 1.048 has 48 gravity points and 48÷4 = 12° Plato. This approximation is pretty good up to about 1.070. After this the approximation begins to deviate from the actual conversion. A conversion table between specific gravity and degrees Plato can easily be made in a spreadsheet using the following formula. An example converting 12° Plato to specific gravity is shown (the order of operations is little confusing at first glance).
Specific gravity = 1 + [Plato ÷ {258.6 - (Plato x 0.88)}] = 1 + [12 ÷ {258.6 - (12 x 0.88)}] = 1 + [12 ÷ {258.6 - 10.6}]= 1 + [12 ÷ {248}] = 1 + [0.048]= 1.048
Dear Mr.Wizard:
I am an extract brewer and recently brewed an oatmeal stout. When it finished aging, I tried a glass. The taste was good but I have some concerns. What can I do to increase head retention? When steeping crushed grains, what is a good method to keep the husks from escaping from the steeping bag? I worry these are going to cause off-flavors but it never fails that some of them slip through the steeping bag.
Lastly, when using oatmeal, I was confused if I should put it in a steeping bag or add it to the pot. I added it directly to the pot and I had a heck of a time siphoning my wort.
Aaron SongerHuntingburg
Indiana
Mr. Wizard replies: This question touches on several good brewing topics. For starters, oatmeal must be mashed to convert the starch into fermentable sugars. If the oatmeal is simply steeped, you will extract starch and viscous gums (beta-glucans) from the oatmeal. The only grains I would use for steeping are crystal malts and dark roasted grains like roasted barley, black patent malt and chocolate malt. All other grains should be mashed in order to convert the starches contained in the grain to fermentable sugars.
Oatmeal is added to beers, especially stouts, because it is believed to enhance the foam stability and body of the brew. Some brewers believe that the beta-glucans increase beer viscosity enough to increase foam stability. Although many brewers share this view, this benefit is arguable. Furthermore, oats are rich in lipids (oil) and lipids are not good for foam. Oatmeal is also well known for making wort separation difficult because of the viscous beta-glucans. Brewers using oatmeal often use it sparingly so that wort separation is not an absolute nightmare.
I believe the proteins found in unmalted grains, like oatmeal and raw barley, are responsible for improved beer foam. When grain is malted these proteins are reduced in size and have different foaming properties compared to the proteins in unmalted grain.
As far as steeping methods go, all grains used for steeping should be placed in a bag unless you plan on straining the steeping grain and water mixture prior to adding your extract, be it DME or liquid extract. I would not worry too much about a few pieces of husk escaping from the steeping bag, but if you are getting a large amount of leakage you may want to find a bag that has a finer mesh.
If I'm reading your question correctly, it sounds like you boiled the oatmeal with the wort. Whether steeping crystal malt, roasted barley or oatmeal, I would not boil the grain, especially without a steeping bag. Many brewers find that boiling grains gives beer an astringent flavor and, as you describe, boiled grain that is not in a steeping bag makes siphoning extremely difficult. Steeping should be performed between 150° and 170° F. |
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