Extract brewing shares many similarities with all-grain brewing, but it has its own set of challenges as well. Many of these challenges have been ignored or given only trivial consideration in homebrewing literature. With that in mind, I've written some articles over the past few years dealing with challenges in extract brewing, especially stovetop extract brewing. These articles include, "The Texas Two-Step" (October 2003), "Extract Experiments" (October 2004), "Steeping" (May-June 2005) and "10 Steps to Better Extract Beer" (October 2005). Two other useful BYO articles include "Boil the Hops Not the Extract," by Steve Bader (October 2002) and the October, 2004 Tips from the Pros column. In this issue, I continue in that series with a look at hopping procedures for extract brewers.
One of the biggest complaints of beginning extract brewers is that their beers do not turn out hoppy enough. Many homebrewers became interested in homebrewing after tasting hoppy pale ales or IPAs. However, their attempts to replicate these hoppy beers on their stovetop often end in disappointment.
Limits to Bitterness
The amount of bitterness in extract beer is primarily limited by two factors. The first is the inherent solubility limit of bittering compounds in wort. Alpha acids are compounds in hops that lend bitterness to beer. When you buy hops, their strength (measured in the percentage of alpha acids) should be given on the package. In the boil, alpha acids are extracted from the hops and the heat of the boil alters their confirmation (isomerizes them). The isomerized alpha acids are primarily what adds bitterness to beer, although similar compounds called beta acids also play a role. Only 20–30% of the alpha acids in hops are extracted and isomerized under typical wort boiling conditions.
There is a limit to the amount of bitterness that can be imparted by boiling hops. Estimates of maximum hop bitterness range from 100–120 International Bittering Units (IBUs). Above this level, adding more hops in the boil does not result in more bitter beer. However, more bitterness could theoretically be obtained by adding hop extracts.
The solubility of (isomerized) alpha acids also varies with wort density — the denser the wort, the less alpha acids will dissolve into it. Given that most stovetop brewers boil a concentrated wort, wort density (measured by most homebrewers as specific gravity) frequently limits the amount of bitterness in their beers.
The second variable influencing bitterness in extract beers is the dilution factor. When stovetop brewers are done boiling their wort, they dilute it with water in their fermenter. The water dilutes not only the sugars in the wort (lowering the specific gravity to its target), but the alpha acids as well. So, if you want to brew 5 gallons (19 L) of beer with 30 IBUs and your post-boil volume is 2.5 gallons (9.5 L), your boiled wort will need to measure 60 IBUs.
The Best Solution
The best solution to increasing the amount of hop bitterness in a stovetop beer is boiling a larger volume of wort. With regards to hopping, there are two benefits to doing this:
First, with a larger volume, you add less dilution water — and consequently experience less dilution of the bittering compounds. Secondly, boiling the extract in more water results in a less dense wort. With a lower density wort, you extract more bitterness from your hops. Other factors, such as boil vigor and if the hops are bagged or not also influence hop bitterness, but not to the degree that wort volume does.
If your limitation to boiling a larger volume is brewpot size, there are a couple options to consider. As you boil, the volume of your wort decreases as water evaporates. If you are already dealing with a small amount of wort, you should consider topping up with boiling water as you boil. Keep a smaller pot of boiling water next to your brewpot and add water to the wort to replace any water lost to evaporation every 10 minutes or so.
Two better options are to boil your wort in more than one pot, thus boiling a larger volume, or make your wort in stages — for example by splitting your wort preparation into two separate boils. If you boil in multiple pots, spread the hops amongst the pots evenly, taking into consideration the size of the pots.
Boiling a larger volume of wort has other benefits as well, most notably limiting the amount of wort darkening that occurs during the boil. The only drawbacks to boiling a larger wort volume are that you need to cool more wort (and you have less dilution water to help you) and you may have trouble maintaining a good rolling boil.
It's fairly easy to cool up to 2.5 gallons (9.5 L) of wort in a sink. Just put the lid on your brewpot after the boil and place the pot in a sink of cold water. Change the water several times, then add ice when the side of the pot feels neither hot nor cold (i.e. when it's around body temperature). A bathtub can be a convenient water bath for holding multiple pots.
If you're boiling 3 gallons (11 L) or more, you'll probably want to invest in a copper immersion chiller (about $35 at most homebrew shops.) If you buy a larger brewpot, but your stove can't bring the full volume to a rolling boil, experiment with the placement of the lid on the pot. Although you don't want to boil wort in a closed pot, leaving the lid mostly on can help your boil vigor and still provide an outlet for steam. If you still can't bring the full volume to a rolling boil, reduce the wort volume to the point that a rolling boil is possible.
Of course, it's been known for a long time that boiling a larger volume of wort leads to better hop utilization — but how big is the effect? To get some idea, see the table on page 30. The table shows the maximum level of bitterness (in IBUs) you can achieve in an extract wort, given your wort volume at the end of the boil.
Estimates for maximum IBUs in both extract late beers and "standard method" beers are given. For the extract late beers, it is assumed that you boil your wort (whatever its volume) with a boil gravity of less than SG 1.050, then add the remainder of your malt extract at the end of the boil. At that boiling gravity, the wort could contain up to 100 IBUs. The maximum IBUs achievable for 5 gallons (19 L) would then depend only on how much you diluted the wort.
For example, lets say you boiled 3 gallons (11 L) of wort down to 2.5 gallons (9.5 L). If the boil gravity was 1.050 or less, and you added enough hops, you should end up with 2.5 gallons (9.5 L) of wort at 100 IBUs. After dilution, you would have 5 gallons (19 L) of wort at 50 IBUs.
The values in the standard method column are calculated in a similar manner, but also figuring in that the boil gravity will be higher at smaller wort volumes. It's important to note that the values in the table are estimates based on the calculations I just described; they "make sense" — and mesh with my brewing experience — but they have not been experimentally verified. Also, note that the table applies to moderate-gravity beers (around OG .048); for bigger beers the values would be lower as the higher gravities would result in lower hop utilization.
Style Follows Size
So what do the numbers mean? Essentially, they mean that the volume of wort you boil determines the styles of beer you can brew successfully. For example, if you are following the "standard" extract instructions of boiling all your malt extract in 1.5 gallons (5.7 L) of water, then diluting to 5 gallons (19 L) after the boil, you can only get about 17 IBUs of bitterness in your beer. With this limitation, your choice of possible beer styles isn't very wide. Two good candidates for this method are British mild ales or Scottish 60-shilling ales. Both of these styles are lightly hopped (target IBUs less than 20), low gravity (original gravity less than 1.040) ales and are dark enough (SRM values of 20–30 are fine) that moderate amounts of wort carmelization won't detract from the beer's look.
By increasing the amount of wort you boil to 2.5 gallons (9.5 L) and switching to the extract late method, you can brew beers with up to 50 IBUs. This will allow you to brew almost any classic beer style, including most pale ales, porters and stouts.
To brew the newer, hoppier styles of American ales — such as American pale ales, ambers, IPAs and double IPAs — you will need to boil at least
3.5 gallons (13 L) of wort.
There are a few other ways to boost the amount of hop bitterness, or the perception of bitterness, in a beer.
Extract brewers should add their hops loose in kettle. Hop bags are convenient, but they limit the degree of hop utilization. Adding some gypsum in the boil — up to 2 tsp. per 5 gallons (19 L) in soft or distilled water — accentuates hop bitterness. Likewise, adding hop aroma by dry hopping increases the perception of hop bitterness slightly. Use up to 2 oz. (57 g) per 5 gallons (19 L). Finally, hop bitterness is more pronounced in drier beers, so always add enough yeast to properly attenuate your beer — yet another reason for making a yeast starter.
In the end, the amount of hop bitterness in your beer needs to be confirmed by your taste buds. If the numbers say your beer is fine, but your tongue says it still isn't hoppy enough, add more hops and boil more wort until you arrive at the taste you want.
Chris Colby is the editor of BYO.