Sunday, August 1, 2010

Wish I could remember the awesome title I had for this post

I guess it's a sign of the times. I was getting in the car to go run (and no, the irony of that is not lost on me) and I had a great idea for the title for a blog entry for Fork and Hay. Now I can't recall what it was. I suppose I'll just have to wing it.

Today we're going to talk about basics. I've written before about a strange flavor change I have detected in my batches of late. I don't know how to classify the taste, but whatever it is it is wrong for the styles I have been making. As I was pondering the latest unusual situation that resulted in an unexpected flavor component in a batch, some pieces of information I had encountered in my seemingly endless web browsing over the last couple of years started to congeal into a possible explanation.

At first, I was all set to blame my 10-gallon batch setup for the problem, because all the faulty brews had been 10 gallon batches. I have noted issues with getting the correct mash temperature before, which has prompted me to pursue designing a RIMS system (which I will hopefully finish this fall). My initial thoughts were that I either had trouble measuring the temperature correctly in the first place, or that the mash tun was doing a poor job of holding the temperature required.

In an attempt to eliminate variables, I made the last four batches (including two I'm going to talk about later which are still fermenting) using the five gallon setup. Two of these were Honey Half-Wit recipes, and I have already chronicled the success of the one that's been kegged and consumed. The other finished batch deviated from expectations, and it was the manner of this deviation that finally helped the light bulb come on, because it told me the problem was not limited to the 10 gallon equipment.

100703 Hook Me Up finished high, a full .007 above the predicted level, and it had a sweeter, thicker taste than I expected it to have. Recalling that the Por Favor and Geordie-Boy batches that weren't successful also tasted thicker and a touch sweeter, I noted that a couple of them had higher than expected finishes as well. As I read more, I learned that what I've been characterizing as "sweet" is really "malty," which is a way of stating that there were a lot non-maltose sugars in the wort, sugars that the yeast could not convert to alcohol. The presence of unfermented sugar in the finished beer helps explain the sweet, thick taste, and it also explains the high finish gravities (because sugar that the yeast can't eat continues to affect specific gravity). What could cause this excess maltiness as a shared characteristic of batches that span yeasts, grain bills, and equipment?

Sacch-re bleu!

There are numerous sources around that describe how mashing works, including a highly informative wiki entry at and this chapter of John Palmer's outstanding book "How To Brew." The essence of the process, as far as the maltiness problem is concerned, is the relative activity of two key enzymes during "saccharification" (the period during the mash where starch converts to sugar): beta amylase and alpha amylase. Beta amylase is the most effective agent in the conversion of mash starches to maltose. Alpha amylase converts some starch to maltose, but it also produces other sugars from starch as well.

Palmer's discussion of saccharification is particularly understandable and suggests the cause of my problem: if  my worts have excess non-fermentable sugar, there is too much alpha amylase action going on and not enough beta amylase activity. The two enzymes work at different temperature ranges, with beta amylase ramping down at about 152 F and alpha amylase picking up at 154 F. The conclusion, therefore, is that if there's too much non-fermentable sugar in the wort, the mash temperature was higher than it should be, because it left the saccharification mostly in the hands of alpha amylase.

So why am I mashing too high? In every batch so far, I have hit the strike water temperatures required by BeerSmith, and I am pretty sure I can eliminate problems with the software as a factor. To investigate further, I opened up BeerSmith to see what components influence the way the equation is solved, but before I describe what I found maybe I should backtrack a little and explain exactly what BeerSmith is doing for me.

Warning: physics content

The basic problem is simple in concept: heat a quantity of water and grain to a specific temperature. If you could do it in a way as simple as it sounds, for instance adding the grain to the water and then heating the result, everything would be ready to go as soon as the whole mash volume hit the temperature target. Doing it that way, you don't have to worry about how much water you're using and how much grain is involved - as long as the mash is fluid enough to allow you to stir it, it will all get to the right temperature at the same time. Of course the problem isn't that simple. I don't have a powerful enough agitator to be able to roll over a suspension of 8-plus pounds of grain in 3 or so gallons of water so that it doesn't scorch.

It's far more practical to heat the water separately and then add the grain into it, stirring to make sure all the grain is well saturated and in suspension. However, if you've ever cooked pasta  (or grits, but of course never instant) you know what happens when you add pasta to boiling water: the boil stops. That's because adding the room-temperature solids to the hot water lowered the overall temperature of the suspension as the pasta took heat out of the water until the whole mass reached thermal equilibrium.

What we're doing in the mash tun is essentially the same thing, but with a slightly different approach. With a single-infusion mash (one where there's only one charge of strike water), we need to know what temperature the water has to be in order to source enough heat to bring the whole volume into equilibrium right at our desired mash temperature. Mathematically, it's simple - all you need to know is the volume of the water you're using, the mass of the grain you're adding, and the grain's starting temperature so you'll know how much heat it's already harboring. (You'd think you could do the same thing with pasta, but there's a catch: you can't heat water to over 212 F because the result isn't water, it's steam, and it's not helping cook your penne to al dente when it rises out of the pot.)

That's pretty basic high-school level physics and chemistry, and as I said before it seemed unlikely to me that BeerSmith could screw the calculations up. As it turns out, BeerSmith has a far more sophisticated model in place that factors in several variables, including:

  • The material used in the mash tun and its weight - because the mash tun itself is not a perfect insulator and will suck heat from the mash both initially and over time. Different materials will have different specific heat values, where specific heat is a measure of how much energy is required to raise the temperature of a gram of the material 1 C. Knowing the material gives you a reasonable ballpark on its specific heat; knowing its mass lets you then calculate how much heat it's going to need as it joins the mash in reaching thermal equilibrium.
  • The starting temperature of the mash tun.
  • The volume of water to be used in the mash (which is internally converted to mass for another specific heat calculation).
  • The weight of the grain bill to be used (but not its specific heat: BeerSmith uses a constant).
  • The starting temperature of the grain.
When you create a batch sheet in BeerSmith it automatically pulls in the grain bill weight from the recipe and the strike water volume from the recipe's mash profile. (It can actually do a lot more than that, but I only use single infusion mashing so there are no other steps.) The mash tun material and weight are defined in the equipment profile for your recipe.

The starting temperature of the mash tun and the starting temperature of the grain are given default values of 72 F by the software.

Now we're getting somewhere...I think

My problem batches were created over a fairly long span of time (from November through May), and the grain storage area in the garage varied from being in the 40's to the 70's during that time. That means that the grain and mash tun temperatures varied that much as well, and you know what? I never changed the values in the software to reflect the current conditions.

Aha! I thought. Let me adjust the grain temperature of a Geordie-Boy batch and see what effect that has on the strike water temperature BeerSmith calculates to hit the target 154 F:

  • 50 F grain: 173 F water
  • 72 F grain: 169.8 F water
These numbers seem to indicate that I should have had lower mash temperatures when the grain was colder than the calculation allowed for, because I used 169 F water instead of the 173 F that was required. Clearly that's not the case, because lower mashing would favor beta amylase activity (as long is it wasn't too low, like below 131 F) and the production of maltose instead of unfermentable sugars. When you add in the fact that I didn't adjust the mash tun temperature either, the "too cold" disparity becomes even greater, with the strike water requirement moving up to 174.1 F when the grain and tun were at 50 F.

The analysis left me puzzled for a while, and then it hit me: it was about the time of the first weird batch that I started heating the strike water directly in the mash tun with my heat sticks. I first did that all the way back in November with 091103 Por Favor, and I've continued that way ever since. You've doubtless spotted the issue by now, and it goes all the way back to the beginning of the physics lesson above. If you heat the water in the mash tun, the mash tun and water are the same temperature all the way along.

Rather than starting with a 50 F or 72 F mash tun, I was starting with a tun at the strike water temperature of 169 F. There's no doubt that having all that extra heat available influenced the mash temperature upward, which could explain the apparent preference for alpha amylase, but what was the real effect? Could it really have been enough to push the mash clear out of the beta amylase range and lead to an excess of unfermentable sugar?

Going back to BeerSmith's calculator, I started doing a little iterative solving, holding the grain temperature constant while changing the mash tun temperature until it and the calculated strike water temperature converged. What I found was startling. The strike water temperature I had been using was up to 5 F too hot, because the number I converged on was around 164 F.

To figure out the effect on the mash temperature, I did a little more iterative solving by changing the mash temperature desired and the tun temperature until the strike water and tun temperatures were both at 169 F. The calculated mash temperature under those conditions was 157.5 F - pretty dramatically above the top of the beta amylase range. No wonder those beers were too malty!

The moral of the story

If anything, this exercise has taught me the value of paying attention to details (again, but if you're a regular reader here you know I'm a slow learner). By not fully understanding what all the factors were that went into the strike water temperature calculation, I wasn't able to adjust for a process change that affected its computational basis. This translated into a probable error of up to 4 F in the mash temperature of several batches, which I now know results in an increase in the ratio of unfermentables to maltose in the wort. Unplanned non-fermentable sugars lead to higher than expected finishing gravities and a maltier taste which, if not properly balanced, might not be desirable.

In short, if you don't know what you're doing, you'll screw up. And that truly is a lesson I keep learning.

Next time (soon, I promise) we'll meet the first post-revelation batch of Geordie-Boy and check in on another batch of Honey Half-Wit.

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