Dextrin Malts, High Gravity & Filtering Water: Mr. Wizard


I understand that DextraPils® gives body and head, but why? What is the process in making this malt and how does it break down in a mash? What type of sugars or starches does it provide? I do know that DextraPils® grain itself is crunchier and not as sweet as 2-row malt. I did a test and brewed my IPA recipe, but left out the DextraPils® and replaced it with 2-row malt. This was only about 5% of the grain bill. My OG went up 3 points. I have my gear dialed in and have been able to duplicate this recipe with the same numbers several times. So if you could please clear up what the science is behind DextraPils® I would greatly appreciate it.
Justin Burdt
Oakland, California

DextraPils® is a specialty malt produced by the Great Western Malting Company located in Vancouver, Washington. DextraPils® is a type of crystal malt that is often referred to as dextrin malt. Other companies produce similar products, for example Briess Malting produces CaraPils® and Weyermann Malting produces Carafoam®, so for the sake of clarity in my answer I will refer to these malts as dextrin malts. These products are known to increase fullness, increase the final gravity and to enhance foam. These same properties are also associated with other types of crystal malt, but the difference is that dextrin malts are no darker than typical Pilsner malt nor do they add the caramel-like flavors associated with darker crystal malts.

All crystal malts are made by converting the starch in malted barley into what is basically wort before the malt is roasted. This is usually done by beginning with “green malt” or malt that has yet to be kilned. The green malt is heated to conversion temperatures (150-160 °F/66-71 °C) without allowing the grain to dry. This process is known as “stewing” and is usually performed in a roasting drum. Under these warm and moist conditions, the enzymes in green malt convert starch into fermentable and un-fermentable sugars, also known as dextrins. Just like with mashing, the stewing temperature affects wort fermentability. Maltsters who produce these types of malts are protective of their processes, but if I had to wager a bet I would guess that the stewing process is carried out at the upper end of alpha-amylase’s temperature range in an effort to minimize the activity of beta-amylase. These conditions would favor the production of dextrins and minimize the production of maltose, which of course is fermentable.

After the conversion rest, the malt is kiln-dried and roasted to promote the Maillard reaction. This is a reaction involving so-called reducing sugars and amino acids. The reducing sugar involved in the reaction can be the monosaccharide glucose, or it can be the one end of a dextrin polymer that is described as the reducing end. Although starch and dextrins in malt will be converted to fermentable sugars in the mashing process, carbohydrates that participate in the Maillard reaction yield compounds that are not converted to fermentable sugars during mashing. Dextrin malt has very little color, so the process must be controlled to limit color development. The malting and stewing conditions and the kilning and roasting profile are critical to minimizing color and flavor development. Under-modified malts are probably used for dextrin malts to limit protein breakdown during malting. The result of the process is a type of crystal malt containing Maillard reaction products (MRPs) with very little color or flavor.

I do not know the exact reason why these malts improve foam stability. The general explanation is that the types of MRPs associated with dextrin malts contain more foam-positive compounds than pale malt types. Under-modification is certainly one way to improve foam stability. Foam is stabilized by foam-positive proteins and the process used to produce dextrin malts clearly results in a greater concentration of these types of proteins than the process used to produce pale malt. Like other crystal malts, dextrin malts do not have to be mashed and homebrewers using extract with specialty malts added by steeping can add dextrin malts to their beers. This topic is really the “black box” of these products; no companies producing very pale dextrin malts explain their proprietary process and seem to take great pleasure in the air of mystique surrounding their products.

One thing that is simple to answer is the reason your OG increased when you replaced the DextraPils® with pale malt. The pale malt has a higher extract yield, but not enough to account for a 3-point increase. You noted in your question that you noticed that DextraPils® is crunchier than 2-row. This is one way to describe the texture of dextrin malt, the description I would use is hard, almost like a rock! You may not have been milling the DextraPils® fine enough to obtain a very good yield. I hope this has given you a little more insight into dextrin malt.


I am currently brewing a high gravity beer (1.097 OG). after 6 days I noticed there were no bubbles in the airlock. I took a gravity reading of 1.034. I poured the sample back into the fermenter and checked the temperature two hours later. The airlock was busily bubbling away at 5 to 6 second intervals. Two days later there were no bubbles in the airlock. I checked the gravity again and got a reading of 1.026. Same thing, two hours later the airlock was bubbling away. Have I discovered a way of unsticking a stuck fermentation? I did use a yeast starter. Is there a percentage of gravity drop before racking into the secondary fermenter? Also I have read about diacetyl rest, does this take place in the primary or secondary fermenter?
Ben Kalota
Jacksonville, Florida

This is one of the questions that makes me scratch my head, and for more reasons than one. My first response actually has nothing at all to do with the question. And that response is “stop pouring samples back into your fermenter!” Taking a sample from a fermenter to check gravity can easily result in the sample being contaminated with bacteria or wild yeast from your gear, therefor returning it to the fermenter is not a practice I would choose to use. I do advocate taking gravity samples to confirm that fermentation has ended and I understand why homebrewers are tempted to return their samples to the fermenter. If you ferment in glass then you can visually determine when things are slowing down. I prefer watching the airlock and the appearance of the fermenter and then taking two or three samples towards the very end to confirm that the gravity has stopped dropping. But that is a different subject.

OK, I am still scratching my head about the observation because I am quite sure that taking a sample, checking its gravity and returning the sample to the fermenter has nothing to do with causing the fermentation to pick up activity. Perhaps pouring the sample back in the fermenter caused enough turbulence to release some dissolved carbon dioxide from the beer, resulting in the bubbles. Or the airlock may have a leak between the rubber stopper and the top of the carboy that was sealed by removing and replacing the airlock. Or maybe you somehow aerated the sample and that really did have an effect on the fermentation. None of these answers are very satisfactory. But one thing I am fairly sure about is that you have not discovered a way to remedy a stuck fermentation!

When brewing high gravity batches there are a few things that are very important. While pitching rate and proper aeration are the obvious things to be mindful of, the importance of these two topics cannot be stressed enough. Yeast strain is also something to carefully consider. Some strains do not perform well with high-gravity wort. Yeast suppliers do an excellent job of describing the strains they sell and I suggest choosing a strain that is described as performing well in high-gravity wort. The use of a yeast nutrient containing zinc is also something to be considered.

Knowing the right point in fermentation to rack a beer to the secondary is hard to determine if you have never brewed the beer before, that is; if one chooses to rack to a secondary fermenter. If you have a beer that you want to move off of yeast for prolonged aging I would wait until the fermentation slows and is about 4-6 points above the expected final gravity. This will allow enough carbon dioxide production during secondary fermentation to purge the headspace of the fermenter of air.

If you are brewing a beer that is not being aged in the secondary, but really just being moved prior to bottling I have a different opinion. I would hold my beer in the fermenter until fermentation is complete and the gravity stops dropping. At this point I would hold the beer for an additional four days for the diacetyl rest, remove the airlock and seal the top of the fermenter with plastic wrap and then move the fermenter to a refrigerator that is set to 34-38 °F (1-4 °C) and leave it in the refrigerator for at least two days. This will help clarify the beer prior to racking. If you have a Cornelius keg you can purge the keg with carbon dioxide before racking and either carbonate in the keg for draft dispense or add sugar and yeast before bottling. Or you can rack to another carboy or bottling bucket. In my opinion, there is really no real benefit to racking beer into a secondary fermenter for a short aging duration.



I got a water quality analysis from my local water department. I am wondering, If I filter my water, does it change the analysis in any significant ways?
Craig Collins
Casper, Wyoming

The answer to this question depends on what type of water filtration that you are planning to use. Carbon filtration is the most common type of home water filtration. Carbon filters contain activated carbon (charcoal) and are primarily used to remove heavy metals, chlorine, chloramines and trihalomethanes from drinking water. Heavy metals and trihalomethanes represent health concerns in drinking water and chlorine and chloramines negatively affect water and beer flavor, so all of these compounds can be removed without having any detrimental effects to your brewing. In short, carbon filtration will not significantly change your water chemistry with respect to the analysis prepared by the local water department, so you do not need to worry about that.

If you use something like a salt-based water softener then you will significantly affect your water since water softeners replace calcium and magnesium with sodium. Although some water contains too much calcium and magnesium, salt-based softeners are not ideal for treating brewing water because of the addition of sodium. In fact, the replacement is a two-to-one multiplier since two sodium ions are added to water for every one calcium or magnesium ion removed.

Salt-based water softeners are commonly used as pretreatment before reverse osmosis membranes. Reverse osmosis filtration of water removes almost all dissolved ions from water leaving the water in a state that is very similar to distilled water. Using reverse osmosis filtration does indeed significantly alter brewing water.

I live in Springfield, Missouri where the ground water contains relatively high levels of calcium and carbonate due to the karst topography of our region. At Springfield Brewing Company we use four types of water treatment to prepare water for brewing. The first filter is a pleated filter to trap solids before the water flows to our carbon filter. Incoming water is then softened, pumped through reverse osmosis membranes and the water is then stored in our ambient water tank.

We remineralize this water depending on the beer we are brewing. If you have water with a nice blend of minerals I recommend simply filtering your water with a carbon filter and adding any minerals that may need a boost.

Issue: March-April 2014