Ask the Experts

Homebrew expert Brad Smith, author of the Beersmith homebrewing software and the voice behind the Beersmith podcast, tackles questions about predicting original gravity, measuring ph, and separating hops from wort.

I recently tried to brew a high-gravity imperial stout using all grain, but my original gravity came in much lower than predicted, and I don’t know why.

Brewing a high-gravity all-grain beer can be a challenge, and getting it right requires some forethought and planning. These beers typically involve original gravities of 1.080 or higher, which means you may be using double the amount of grain (or more) that you typically brew with. Not only does this push the limited capacity of your mash tun, but it also lowers the efficiency of your brewing system. Lower efficiency means lower gravities and even more grain to reach your target.

If we look at a normal lautering process, we see that the gravity coming out of the mash tun during the early runnings is quite high, and then it tapers off as we run more wort through the grain bed. In fact, it is not uncommon to get two-thirds of the gravity points extracted in the first half of the runnings and only one-third of the gravity points in the second half of the runnings. There is a method called “parti-gyle” brewing that does exactly this—makes one high-gravity beer from the first runnings and another low-gravity beer from the second half. (For more information about parti-gyle, see “Practical Parti-gyle Brewing” in the February/march 2015 issue.)

Lets consider a 1.040 beer brewed on a 10-gallon (38 l) system. At 72 percent brewhouse efficiency, it would take about 15 pounds (6.8 kg) of grain to reach 1.040 original gravity assuming just over 13 gallons (49 l) of wort is produced pre-boil.

If we up that to a 1.080 beer, we now need 30 pounds (13.6 kg), or double the amount of grain, to reach the higher gravity assuming the same efficiency. The problem is that we’re still producing only 13 gallons (49 l) of wort from the mash, so we’ve doubled the amount of grain but are making the same amount of wort.

Comparing the two cases of normal vs. big beer, we can see that doubling the amount of grain to produce the same amount of wort is much the same as the parti-gyle method above. When we make a normal beer, we have enough water running through the grain bed to get good extraction, but when we double the grain used, we’re

taking the high-gravity runnings (the first two thirds of gravity) but discarding the tail end (the last one third), so mashing a big beer is much less efficient.

The bottom line is that when you brew a big beer, you will get lower efficiency. For an extreme case like this where we’ve doubled the grain used, it could be as much as 25–33 percent lower, which means our 72 percent brewhouse efficiency could drop as low as 50–60 percent. This means we would need another 10 pounds (4.5 kg) of grain to reach our 1.080 target! In practice, it may not be quite that bad, but even using a 60 percent efficiency number means an extra 6 pounds (2.7 kg) or 36 pounds total (16.3 kg) is needed for our 1.080 beer.

I’ve bought lactic acid to adjust my mash ph, but when is the best time to measure my ph and then add the lactic acid?

Mash ph is most critical during the main conversion step, when the complex sugars in the crushed grains are being converted to simpler sugar chains that yeast can consume. This occurs in the temperature range of roughly 148–156°F (64–69°C), which is where most brewers mash in when doing a single-infusion mash. This is the phase when you need to get the ph right.

Today, we use highly modified malts that have a lot of enzymes to facilitate this sugar conversion, which means the conversion can happen very rapidly. In some cases, the mash conversion can be complete in as little as 20 minutes. So in an ideal world, you would add your lactic acid before you mash in so you can precisely hit your target mash ph (typically the 5.2–5.6 range) up front.

The reality is that this can be difficult to achieve. You can’t measure your mash ph until 5–10 minutes after you’ve mashed in, and an accurate ph reading is needed to calculate the lactic acid needed as an adjustment. However, you can predict the mash ph using software, although the prediction may not be perfect.

So the compromise I’ve reached is that I estimate my mash ph from the grain bill and water profile using software up front, and use that to estimate how much lactic acid I need to get myself into the 5.2–5.6 ph range. Then after I’ve had a chance to mash in and let the ph settle, I take a ph reading and verify that I’ve reached the target ph I was shooting for. If I’m off substantially at this point, I can make a second lactic-acid addition to reach the target level.

This compromise lets me hit my target range up front to cover cases where the mash conversion may complete quickly and then adjust it if needed after I’ve mashed in.

I’m finding it difficult to separate the hops from the wort after the boil, and I’m concerned spent hops will clog up my chiller. What do you recommend?

There are basically three different types of devices that contain hops matter and separate it from the wort. Each has its advantages and disadvantages. First, you can bag your hops in a nylon or muslin bag. Second, you can consider a hop basket, which is usually made of a fine screen that typically hangs from the top of the boil pot. Finally, you can consider a screen/ device that attaches to the output from the kettle that filters wort as it is drained from the kettle after the boil.

Using a hop bag is probably the simplest

method and the first one many brewers use when learning to brew. A hop bag can be quite effective at containing hops trub, and if you use a large-enough bag, it should have minimal impact on hops utilization. Some bags can even be cleaned and reused. The only limitations to this method are that it doesn’t easily allow for multiple boil additions, unless you use a lot of bags, and it won’t filter out grain trub—the little bits of grain left after the boil.

A hop basket, typically made from a fine metal screen or mesh, behaves much like a grain bag that hangs off the edge of the pot but allows multiple hops additions. Obviously, you need to select one with enough depth/capacity for your planned usage, and you need to pick the right screen size to prevent clogging. When making highly hopped beers, clogging of the screen during use can be a problem, and in some cases, it can be difficult to get the fine screen perfectly clean.

The last type of device is similar to a hop basket, but it sits at the bottom of the kettle and filters the outlet used to drain the kettle. In this case, loose hops are pitched right into the kettle and filtered as the wort is drained at the end of the boil. One advantage is that the filter will usually trap a lot of the grain trub along with the hops trub as both can potentially clog your chiller. Depending on the design, these filters can also clog during use or be hard to clean. At the moment on my own system, I’m using an Anvil Kettle Strainer, which is made from a fine stainless-steel braid instead of a screen. It attaches directly to the kettle drain tube. It has worked well for me and is easy to clean, though I know some people have had issues with clogging.

As you can see, none of these devices is perfect, but they do help reduce trub going into your chiller and fermentor. I do recommend that after you use your plate or counter-flow chiller, you immediately backflush it as this is probably the best ensurance against clogging.

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