Ask the Troubleshooter
Dave Miller on...
Mashing and Protein Rests, Dry Hopping, False Bottom Materials, and Single-Infusion vs. Step and Decoction Mashing

by Dave Miller
Republished from BrewingTechniques' September/October 1994.

Malts, mashing, dry-hopping, and equipment design, the Troubleshooter has something to say about them all.


Q:I have two questions for which I can't get good answers from local homebrew supply stores.

I am a new full-mash brewer. I have been using highly modified two-row pale malt with 10% adjuncts. When mashing on cooler days, I find it hard to keep a steady mash temperature in my plastic mash tun. Typically it drops to about 135 °F (57 °C) after 30 min. I wonder if I am performing a protein rest by accident? Is a protein rest for highly modified two-row malt beneficial, even though it is technically not required? Will I help the mash if I add a higher percentage of adjuncts such as Carapils or crystal?

DM: I doubt that you are getting much of a protein rest with your mash procedure. Most of the protein-converting enzymes in malt are active between 113 °F and 140 °F (45 °C and 60 °C). At higher temperatures, they are deactivated (a fancy chemical term for cooked). I assume you are starting your mash at around 150 °F (66 °C) - it sounds like you are trying to do a single-temperature infusion mash - so most of the protein-converting enzymes will be out of commission before the temperature drops back to protein rest range.

If you get any protein conversion, it certainly won't hurt anything. The only problem you can have from a protein rest is that, if you let it go on too long, you may get so much protein breakdown that you don't have enough large and medium-sized protein molecules in your wort, to the detriment of body and foam retention. For the reasons I mentioned in the previous paragraph, though, I doubt this could happen to you.

If I were you, I would be more concerned about the starch conversion. The speed and efficiency of the starch-to-sugar breakdown depends very much on temperature, and I would be leery of any process that did not give the mash at least 0.5 h at 150 °F (66 °C) or higher. I know that the big commercial breweries often show conversion in 10 min, but their malt is crushed a lot better than ours. They use multistep mashes that allow the grain interiors to absorb water and soften before they hit the critical temperature.

One indicator of whether you are getting full conversion is the extract yield of your grain; however, problems in other areas, including sparging, can also produce low yields. Another possible indicator is starch haze and a starchy taste in the finished beers.

You would almost certainly get better results if you did your mashes in a kettle that can be heated on the stove, which would allow you to maintain starch conversion temperature for 1 h. If you can't use a kettle, at least wrap some insulation around your plastic bucket mash tun. I bet if you think about it you can find a way to redeploy your brewing vessels so you can heat the mash. Such an arrangement would even enable you to run a step mash deliberately, if you want.

A quibble: products like Carapils (dextrin malt) and crystal malt are not really adjuncts. Adjunct is a specific technical term in brewing and refers to unmalted cereals, such as corn, which are used to augment the starches contained in barley malt. Adjuncts must be cooked before being added to the mash tun. The best form of adjuncts for home brewers is flakes, which have been precooked during the manufacturing process.

The grains you refer to are called specialty malts, which are made by modifying the malting process in various ways. They require no cooking. The specialty malts you mention are little affected by protein-degrading enzymes, though some others, such as rye malt or wheat malt, do contain considerable protein and would be affected. When using such high-protein specialty malts, or high-protein adjuncts like oat or barley flakes, a protein rest is a good idea. In such cases, the protein rest must precede the starch conversion rest. For more discussion of this issue, see the last question in this article.


Q: I have dry hopped at least five batches with success. I mostly use whole hop flowers in a gauze cloth bag that I steam sterilize in my pressure cooker. On my last batch, two days after adding the hops, I noticed a funny smell. I think my beer developed an infection. Could this be from the hops? Do breweries like Anchor and Sierra Nevada sterilize their hops?

When I put the hops in, I also added an extra dose of good yeast slurry to carbonate the beer in the keg and produce a well-attenuated ale. Could this have been the source of the infection? The slurry was produced by a local homebrew supply store and smelled healthy when I pitched it.

DM: I don't know of any brewery that sterilizes their dry hops. The only ways to sterilize something are with heat - which will drastically affect the hops' aroma - and with sterilizing chemicals, such as chlorine, which will affect the beer and the hops as well.

Actually, you might be able to sterilize hops without wrecking them by using irradiation. Although legal and approved for use on herbs and spices (including hops, presumably), no one uses it because it is an elaborate, expensive, dangerous process that has met strong consumer resistance for both health and environmental reasons. Only one commercial irradiator is currently in operation (in Florida).

Another method proposed in the course of my research is oxygen deprivation through saturation with carbon dioxide. Placing herbs in an environment flooded with carbon dioxide and leaving them for a few days will kill bugs; presumably it will also kill aerobic bacteria. Perhaps some enterprising individual can follow up with some careful research on the use of this technique for hops.

The only real way to ensure the "clean" addition of hop essences is through the use of hop extracts. They are free of not only contaminating bacteria but of pesticide residues as well. This option is favored by some of the larger breweries because of severity of loss if even one batch goes bad. Solvent-based extracts are particularly user-friendly because they can be added at any stage in the process.

In any case, the widespread successful use of dry hopping both in this country and abroad is a pretty compelling argument that the procedure is safe. Your own previous successful experience with it also seems to indicate that it was not the source of your infection.

Although I hesitate to blame your homebrew shop, it seems likely that the yeast slurry was the source of your problem, despite the fact that it smelled OK when you put it in the keg. Where did the slurry come from? If the original source was a dried yeast, it was almost certainly contaminated to some degree, and some contaminants (wild yeasts, for example) grow rather slowly, often taking a few repitchings before they multiply sufficiently to make their presence felt - or tasted - in the finished beer.

The other possibility is that your keg was not clean enough and was the source of the infection. It might just be a coincidence that inadequate cleaning procedures caught up with you on the very same batch that you decided to try a fresh yeast slurry.

In any case, the next step is to thoroughly clean and sanitize your keg. This means removing and disassembling the poppet valves and cleaning them by hand, along with everything else that you can reach. The spear is a problem; the best you can do is to pump cleaning solution through it. All told, a pain in the neck, but the alternative - more spoiled beer - is worse.

Unless your beer is quite old at kegging, you don't need a new yeast slurry to get a second (carbonation) fermentation in the keg. Unless it is a wild superattenuative strain, it won't do any more attenuating than your pitching yeast did. But you should consider artificial carbonation, which has the advantage of leaving much less yeast in the keg and giving you finished beer much sooner.


Q: I am having a hard time finding an appropriate material to fabricate a false bottom for my half-keg gravity brewing setup. Should I go to a brewing equipment manufacturer, or is there a material I can find at a non-brewing specific source? I have tried a heavy-gauge stainless steel screen, but the holes-to-surface-area ratio was too high (disaster).

DM: I suggest a manifold or ring of copper tubing with slots cut in the bottom side. Rings are easiest. Get a length of flexible copper tubing at a hardware or plumbing supply store. Also get a cap to close one end. Bend the ring to fit in the bottom of your lauter tun. Then use a hacksaw and cut the slots 1 in. apart. That should give enough drainage. The ring can be attached to your lauter tun tap with a compression fitting.

Although removable false bottoms are easier to clean, drainage rings or manifolds are much easier and cheaper to make. And because you use them on the hot side of the process, a sparkling-like-new cleaning job is not necessary. Just backflush the ring with water through the tap after each use to remove the trapped pieces of husk and grits.

If you really want a false bottom, use a sheet of copper and cut slots in it about 2-3 in. long, in parallel rows, 0.5 in. apart. The false bottom must be a very close fit to the sides of the lauter tun. Use short lengths of copper pipe to hold the false bottom up above the tap.


Q: I am confused. I am a beginning all-grain home brewer and have learned a lot from friends at a local homebrew shop. One thing they all agree on is that single-infusion mashing is the way to go. Most of the books I have, particularly yours and Papazian's, use mostly step mashes (except for ales), so I have been eager to try them. But in a previous issue of BrewingTechniques, you state that you now use single infusion. What are the advantages/disadvantages of step mashing? What do you recommend? I am under the impression that step mashing is required for six-row malts and German and Belgium malts, and that six-row malts are desirable if you use many adjuncts because of their high enzyme content. What's the scoop?

DM: Sorry to confuse you, but live and learn, as they say. I was dragged down the single-infusion path kicking and screaming, and nothing but money could have done it. When you work in a brewpub, you work with equipment that, although very flexible and refined in some ways, is in other respects more limited than the average home brewery. Our brewing system uses a combination mash/lauter tun which has some insulation but no means of being heated. It is therefore limited to single-infusion mashing. To fit it with steam coils or jackets would have added many thousands of dollars to the price. We went with the basic design, which is similar to what you will find in the majority of pub breweries.

Since I began working at the pub, I have run across a lot of discussion about the merits of step vs. infusion mashing. Dr. Lewis at UC-Davis, long a proponent of single infusion, now seems to believe that the advantage of step mashing is that it allows one to get a higher extract yield without resorting to high mash temperatures (such as 158 °F [70 °C]) (1). Such high temperatures give the best yield in single-infusion mashing but have the undesirable side effect of producing a wort high in unfermentable carbohydrates.

Other research suggests that mash thickness is a critical parameter. Most infusion mashes (single or step) are run pretty thin, which is appropriate for starch conversion. For protein conversion, however, the mash must be stiff. George Fix has suggested that what he calls a "homebrew mash" - running the protein rest thick, then infusing with boiling water to raise the temperature to starch conversion range. This may be the ideal method because it creates optimum conditions for both sets of enzymes (proteases and amylases).

Now, back to your specific questions: First, two-row malt is preferred for single-infusion mashes because it is lower in protein than six-row malt and generally causes fewer problems with colloidal (haze) stability. Two-row malt is also lower in enzymes (hence the preference for six-row when using adjuncts).

We use domestic two-row malt as the basis for all our recipes. This choice is based on a number of factors, including cost and suitability to our brewing system.

American two-row malt stands somewhere between six-row and European two-row in its properties. Its protein content is higher than the best European two-row malt but lower than six-row malt; conversely, American two-row malt's enzymes are lower than in six-row malt, but much higher than in many European two-row malts. Price is a bit higher than six-row, but considerably lower than that of imported malts.

Does it work? Well, our beers are good. I think that we might be able to get more colloidal stability by using the European pale malts, or, alternatively, by using a step mash process. I have done a few batches with imported pale malts, but not enough to draw any definite conclusions about how much difference they would make. Step mashing is impossible with our mash/lauter tun. But stability is not that critical for a brewpub. The beer is always drunk quickly, and it is not subjected to cycles of warming and cooling. It is pretty hazy coming out of the unitank, but Celite 512 covers a multitude of sins.

One other advantage sometimes touted for step mashing is that it increases the amino acid content of the wort. Although this is true, in practice beers made from all-malt grists will always have plenty of amino acids for the yeast to use, if one is using modern, fully modified malt.

I guess I've answered your question about the advantages of step mashing. Disadvantages? Lower foam stability, primarily. Possibly less body, if the rest goes on too long. Other than that, time and trouble - and money, in a commercial operation. Again, the lower foam stability is most obvious in beers of low gravity or in those brewed with a high proportion of corn or rice.

Step-mashing is certainly preferable for six-row malts, because of their high protein content. Nonetheless, I have a sneaking suspicion that you could probably do without it, at least in a brewpub or home brewing situation.

The more important question is, why use six-row malt? Its only advantages are price and enzymes. Price is not that big an issue for small-scale brewers; six-row malt costs only a few cents a pound less than two-row, which is not that significant for us. Its enzyme content is not that much higher than domestic two-row. Although you may run into trouble if you try to convert 30% adjuncts with British pale ale malt, Harrington or Klages pale two-row will work fine.

As far as mashing German and Belgian malts, I can tell you from first-hand experience that Belgian malts definitely do not require step mashing. Also, a growing number of German breweries are using single-infusion mashing to produce their pale lagers, mostly because single infusion is the quickest mash method and has the lowest energy costs. Even in Germany, money talks. Again, the uniform modification of modern malt is what makes this feasible.

As far as I can see, the big issue these days is not step vs. single-infusion mashing. It is infusion vs. decoction. Although it is possible to brew the majority of beer styles successfully using an infusion mash, there are some styles for which decoction is preferable. Examples include German wheat beers and dark German lager styles including bocks, dunkels, and Marzen beers.

Reasons for the advantage all center on the boiling of the mash, which liberates undermodified starches (this helps a lot with wheat malt) and extracts more of the flavor and color from dark malts such as Munich and caramel malts. Although I have been able to brew good Marzen and Doppelbock at my brewery, the beers lack the utter smoothness of the best German examples. I believe that the reason is that, in order to get the color, flavor, and aroma of the style, I have to use relatively high proportions of dark grains such as Munich, Aromatic, and dark caramel. Using a decoction mash, I would be able to get the characteristics I want with lower proportions, and avoid the roughness these grains can impart. It also seems to be the case that, given a similar grist, decoction will usually give a smoother finish than infusion mashing. This seems counterintuitive - you would think that boiling the mash would extract more tannins and rough, sharp flavors from the husks - but the opposite appears to be the case.

I welcome comments on this issue from brewers with more decoction experience than I have.


(1) Michael Lewis, The New Brewer 10 (4), 31-35 (1993).

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