Republished from BrewingTechniques' September/October 1996.

Is Copper Toxic?

Copper is not leached out unless the cooking medium is acidic. Water is not acidic, which is why copper supply pipes can be used safely. However, beer wort is acidic, perhaps not as much as tomato sauce, but acidic nevertheless. And corroded copper should definitely be avoided in all cases.

A: I don't think I ever said "unequivocally" that copper is not toxic. What I did say is that using copper brewing equipment does not pose a health hazard. I will add here that copper in very high concentrations is toxic, especially to lower organisms such as fungi (including yeast) and algae. Certain copper compounds have found wide use as fungicides. On the other hand, human beings require about 2 mg of copper per day for good health. Copper forms a part of some enzymes that are essential to normal cellular function. Yeast also requires trace amounts of copper for its metabolism, and some modern all-stainless steel breweries have had to add copper to prevent hung fermentations. In this respect, copper is no different from many other substances, where a high concentration is toxic but the correct amount is essential.

Copper is considerably more resistant to attack by acids than the writer believes. Diluted nonoxidizing acids, including hydrochloric and sulfuric acid, have no effect on it in the absence of an oxidizing agent. It is only oxidizing acids (for example, nitric) that are capable of attacking it in dilute concentrations. In practical brewing situations, the use of copper equipment will increase the copper content of the wort slightly, but not to the point where it would damage the health of the yeast or the human consumer.

Copper has been used in brewing for centuries all over the beer-drinking world. And copper brew kettles, unlike copper saucepans and frying pans, have never been tinned. The tinning of copper saucepans is applied mainly to give a very smooth surface and to prevent the discoloration of certain foods that can interact with copper. Beer wort is not one of these.

One of the most famous examples of an all-copper brewery is the Pilsner Urquell facility in the Czech Republic. Brew kettles, mash mixers, decoction kettles, and lauter tuns are all built from copper. The triple decoction schedule and very long boil time result in considerable copper pick-up. Nonetheless, the yeast suffers no apparent harm, and if the yeast doesn't, neither will the consumer.

Cleaning Copper

A: First of all, don't worry about copper interacting with wort (see the previous question and answer). Second, copper doesn't need a protective coating. It sounds like you are describing stainless steel, which does require an oxide layer.

As far as basic versus acid reactions with copper, in my experience a weakly acidic solution such as beer wort does not form any sort of coating on copper. My immersion cooler always came out of the kettle as bright and shiny as if I had scrubbed it with a Brillo pad. An oxidizing acid such as nitric will form a layer of copper oxide on the surface of copper, but this is not "protective"; it does not form an impervious layer that inhibits further oxidation of the metal underneath. Copper oxide is easily penetrated and removed from the surface of the metal.

A nonoxidizing acid, such as phosphoric or hydrochloric, will leave copper bright and shiny and remove any corrosion from the surface. If your B-Brite causes the copper of your wort chiller to tarnish, you might want to follow it up with an acid cleaner.

A number of acid cleaners are available on the market; your homebrew supply shop should be able to order some for you. Just make sure the cleaner you choose does not contain an oxidizing acid such as nitric - you or your shop may have to double-check this with the manufacturer. On the other hand, for cleaning or acid-rinsing stainless steel, a formulation that includes nitric acid is a good idea, because it will help maintain the oxide layer on the surface.

Calculating Strike Water Temperatures

A: There is a way of calculating the numbers you want, but you have to choose one or the other - volume or temperature. When you decide how hot the water will be, you can then calculate the amount to be added to raise the mash a specific number of degrees. It's trickier to calculate a decoction, because it is hard to determine the specific heat of the decoction. In general, you try to pull the stiffest portion of the mash for the decoction, but you can't separate the water from the grist to determine the exact proportions.

I learned the following basic formula for figuring the temperature of a mixture from Dan Carey in a talk he gave at the 1988 AHA conference:
Aa + Bb = Cc
The capital letters A, B, and C stand for the specific heats of grain, water, and the mash, respectively, and the lower case letters stand for temperatures of the same variables. What the formula says is that the product of the temperature and specific heat of a mixture will be equal to the sum of the products of the specific heat and temperature of the two substances that make up the mixture - in this case, water and grist.

I use this formula to calculate the strike temperature of my water for making a mash. For example, suppose my recipe calls for 825 lb of malt, and I want to use 285 gal of water to make up the mash, which should have a temperature of 153°F (67°C). To avoid a lot of extra calculations, I assign a value - 1 - to the specific heat of 1 gal of water. I assign the correct relative value - 0.05 - to the specific heat of 1 lb of grain (0.05 is correct for barley malt; it may not be exactly right for flakes, but it's close enough). If I then measure the temperature of the grain as 70°F (21°C), for example, I can calculate the correct strike temperature for the water.

First, I calculate the specific heat of the grain (A): 825 X 0.05, or 41.25. The specific heat of the water (B) is 285. And the specific heat of the mash (C) will be the sum of those two, or 326.25. The temperature of the grain (a) is 70°F (21°C), the temperature of the mash (c) should be 153°F (67°C), and the temperature of the strike water (b) is the unknown.

To solve for b, we simply work out the calculations:

Aa = 41.25 X 70 = 2887.5
Cc = 326.25 X 153 = 49916.25
Bb = 285b
2887.5 + 285b = 49916.25
285b = 49916.25 - 2887.5 = 47028.75
b = 47028.75/285 = 165.013°F (~74°C)

You can use the same formula to calculate the effect of adding hot water, or a boiling decoction, to an existing mash. Just multiply the specific heat by the temperature of the existing mash and use for Aa. As I mentioned before, the only problem is knowing the amount of grist and water in your decoction so you can get an accurate figure. In practice, you will have to learn by trial and error how big a decoction is needed for a desired temperature rise.

In fact, even for calculating the strike temperature of an infusion mash, the formula is not the last word. Real mashes take place inside a mash tun, and the mash tun, unless you preheat it, will absorb heat and lower the temperature of the mash considerably below its calculated value.

You can compensate for this heat loss, however. For home brewers using a mash tun that cannot be exposed to heat, such as your picnic cooler, I suggest making some test runs to determine how much heat the walls of the vessel absorb. Make up a quantity of water at your usual mash temperature, with a specific heat equal to that of your average mash. For example, a 5-gal batch using 8 lb of malt would have a specific heat of (5 X 1) + (8 X 0.05) = 5.4. Therefore, you'd use 5.4 gal of water heated to, say, 153°F (67°C) for the test run. Put this in your mash tun and let it stand, covered, for 5 minutes. Stir well. Then check the temperature. Most of the drop during the first few minutes will be from heat losses to the cold walls and bottom of the mash tun.

The easiest way to deal with heat absorption by the mash tun is to determine the heat loss in this way, then use mash water that has been overheated to compensate. For example, you need 165°F (74°C) mash water to make a 153°F (67°C) mash. But your mash tun, you discover, will soak up about 5°F (3 °C) in the first few minutes. This means you need to use 170°F (77°C) water, and let it sit in the mash tun for 5 minutes before adding your grain.

As an alternative, you can preheat your mash tun with superheated water, which you then return to your kettle and use for mashing in. This is the way we do it at my brewpub. We pump 12 bbl of very hot (190°F [88°C]) water into the mash tun, then return it to the hot liquor tank before mashing in. This enables us to use a strike temperature close to the theoretical value calculated by the Aa + Bb = Cc formula. If we didn't preheat, we would have to use a strike temperature about 10°F (6 °C) higher than that.

Why is it worth bothering with preheating? Mainly because I am scared to death of scalding the malt enzymes. Our grist is mixed with hot water as it falls into the mash tun. When you are making up a mash with 800 lb of grain and 9 bbl of water, this type of mixing is a lot easier than bringing in the water and then stirring the grain in by hand. (Of course, if we had motor-driven rakes . . .) And if we did not preheat the mash tun, we would have to use a strike temperature that would make a mash hot enough to scald the amylase enzymes, especially the beta-amylase, which cannot survive very long at temperatures in the high 150s °F (68-70 °C). No matter how hard we stirred, it would take 10 minutes or so for the superheated mash to settle into the desired temperature, and during that time a lot of beta-amylase would be lost.

I guess you can see that this all boils down to a trade-off. I don't want to kill enzymes, and I don't want to stir the mash any more than I have to. We also have large seasonal variations in ambient temperature, a problem solved by preheating. So I spend half an hour preheating the mash tun. For home brewers, I don't think this is necessary. You can just bring the hot water into the mash tun and let it settle down before you stir in the crushed malt.

Pitching and Lag Times

A: Our airlock sometimes starts bubbling almost as soon as we get the wort into the fermentor, but it usually takes 6-8 hours before you see the kind of strong, continuous bubbling that says the fermentation is going full blast. This is true with ales. For lagers, it could take as long as 12-16 hours. And even then, "full blast" is not quite as full as it is for an ale. I would say that if you don't see kräusen (thick layer of foam at the surface of the wort) at least beginning to form within those time limits, your fermentation is going to be weak and problematic.

There has been a lot of discussion about cold trub in BrewingTechniques recently (see reference 2 and pages 14-19 of this issue), but I welcome the opportunity to restate my belief that you should pitch the yeast as soon as the wort is cool. If you choose to try to separate the cold trub from the wort, do it after pitching. That way, the yeast will get the benefit of the trub lipids during the first stages of growth.

How Important is pH?

A: In some places, it may be possible to get away with this. Most water supplies, however, are better suited to one type of beer than another. For example, here in the middle of Tennessee our surface water is moderately alkaline - about 60 ppm total alkalinity. You can brew just about any kind of beer using this water, and even with very light beers the mash pH will not be so far off that you don't get conversion. For maximum extract, however, adding calcium chloride to the mash (which lowers the pH) definitely helps. Also, the beer will be smoother if you adjust the sparge water pH with acid. I have been to brewpubs that make no attempt to control pH, and in almost every case I found that some of their beers - usually the darker ones - were better than others.

My experience agrees with what George Fix pointed out in a talk at the 1995 IBS National Microbrewers and Pubbrewers Conference in Austin, Texas. He said that what he often finds is not that beers with a high pH (the most common deviation) are undrinkable, but that they are not as good as they could be.

pH measurement and adjustment are time-consuming, especially for the first few batches. Nevertheless, I think all-grain home brewers who take the time and trouble will find it worthwhile. A batch of all-grain beer takes at least 6 or 7 hours to make. An extra 15 minutes is not that big a deal. As far as cost goes, a bargain-basement pH meter or even a box of Merck pH strips is accurate enough if used carefully. Again, compared to the value of your time and the cost of your whole brewing kit, it's not that big a deal, and you may find it worth the effort.

References

(2) Dave Miller, "Q&A with the Troubleshooter," BrewingTechniques 4 (1), pp. 36-40 (January/February 1996).

Correction The last installment of The Troubleshooter included an illustration of a manometer setup used to monitor lautering progress in terms of suction on the grain bed. Some information shown in the drawing may be misleading. The water level shown in the drawing is the level at the beginning of recirculation; as the wort clarifies and the grain bed pulls together, the level in the tube will drop gradually. A rise in the water level can alert you to a possible blockage that needs to be flushed out.