Attenuation

Attenuation

How To Improve your Attenuation

Those that know me know that I have a knack of brewing outside the box. A few of my beers are under 4% abv, Those I call Starters, They usually have real big flavor and have even won awards, but a disproportionate number of my beers are big beers, 7-8% seems to be a “normal” gravity and very frequently (about 1 out of every 3) make what I call “Century Beers” or beers over 10% abv or over 1.100 OG.

Why do we even care about attenuation? Attenuation is a measure of how much of the sugar in the wort is converted into alcohol. The lower the attenuation, the more sugars are not fermented and the sweeter the resulting beer though we definitely want to avoid the dreaded cloyingly sweet beer. In a small to normal strength beer fairly big swings in attenuation, while noticeable, are not going to push the beer into what many would consider an undrinkable category. The same percentage change will have a significantly larger impact of a big to monster beer. To get the beer we truly want we must control attenuation to hit a desirable, and targeted, FG.

These are guidelines, intended only to aide you in your recipe design and brewing process. It is important to see how your system and your procedures react to what I suggest below. We are about to enter the Art of Brewing because where science stops, Art begins.

When you brew a large number of “Century Beers” it is important to have some concept of how to predict your Final Gravity. The caveats, There are many variables that impact FG, and thus attenuation, (which we will discuss later) and very little is written on how to do this. None of the brewing software packages do this and no literature that I have found really goes into the prediction of FG. I intend to present a common sense approach to predicting FG, especially for big beers.

As with most things with brewing I am relying on consistency to keep many of the factors the same. Certainly by not being consistent repeatability suffers. Each of us brews on our own system and that system, including the procedures we follow, determines the characteristics of the beer we produce. By maintaining that consistency and altering specific parameters we can manipulate results. Below is a graph from Noonan’s book.

Every strain of yeast will perform differently, and that yeast will react somewhat differently to different systems, but by graphing our results in a similar fashion we can learn to predict what attenuation we will get under a given set of circumstances. Is it fool-proof? No, but over time you will learn produce beer much closer to what you predict than you do now.

The first step is to look at your grain bill, or rather just the grain portion of the grain bill, no sugars or extracts as we will address them later. Let’s assume that these grains give us an estimated 1.080 contribution to our OG. We will also assume that our selected yeast and mash profile will yield an attenuation of 75%. Given this, the contribution the FG contribution would be 1.020, [((1-.75)*(1.080-1))+1]. We could decrease this attenuation by about 10% by raising the mash temp from 149°F to 158°F. This would give us a predicted FG of 1.028, [((1-.65)*(1.080-1))+1] These calculations are based on numbers contained in Noonan’s book.

This chart is an interpretation of attenuation in an infusion mash from Noonan’s book. With a single infusion mash at 149°F Noonan says in New Brewing Lager Beer an attenuation of 75-80% usually results.

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I also find that if I step mash a normal grist (the same 1.080 OG used above), that is one without a lot of carapils, crystal or dark malts, a 146°/156° F step mash gives me about a 10% increase in attenuation. This would give me a 1.013 predicted FG, [((1-.85)*(1.080-1))+1]. I would suggest that you verify this with your own brewing setup.

One important factor is that as the beers get bigger, your attenuation must improve to keep your beers in balance. Attenuation and fermentability go hand in hand.

There are four main areas where we can impact our attenuation. The Grain Bill, The Mash, The Yeast, and the Fermentation. By manipulating these portions of our process we can alter the attenuation we get.

Grain Bill

• Grain Bill: Keep highly dextrinous malts such as Carapils, Crystal, and Roasted grains low, keep low fermentable extracts (Laaglanders) low.
• Use Highly Fermentable Sugars: such as corn sugar, table sugar, brown sugar, raw sugar, candi sugar, honey, maple syrup, molasses, etc. These sugars boost alcohol without increasing FG. Estimate your FG without any sugar added.

Mash

• Single Infusion Mash at a low temp (i.e. 149°F): This is the temp where starch is100% soluble and the enzymes have complete access. For that reason it is the minimum temperature that Noonan recommends for a mash.
• Mash longer (up to 2+ hours): It doesn’t necessarily take this long to “convert” the starches to sugars, but by continuing the mash beyond “conversion” some of the non-fermentable complex sugars will be broken down by the enzymes into fermentable sugars resulting in a more fermentable wort.
• Step Mash (i.e. 146°/156°F): This puts the enzymes into their optimum performance temperatures, and usually results in a longer mash. I have gotten up to a 10% boost in attenuation doing this.
• Use a Thinner Mash: A thin mash (>2 quarts/pound) results in a more fermentable mash because the sugars are less concentrated and thus there is less inhibitation on the enzymes. If you are performing a multi-rest mash a thicker mash is better because the enzymes are not denatured as quickly when you step the temperature up. This is because of the lower heat capacity of grain as compared to water.

Yeast

• Yeast Choice: Yeasts are normally chosen because of flavor characteristics for the style of beer to be brewed. Additionally we need to look at attenuation. One key characteristic of yeast is their ability to ferment Maltotriose. Many studies have indicated that this is the primary factor in attenuation. Maltotriose is a trisachride and the second most common sugar in wort (13-19% of fermentables). Most yeast can consume about half the Maltotriose present. Interestingly Lager yeast does a better job of utilizing Maltotriose than does Ale yeast. In general, use a yeast rated for the degree of attenuation that you require.
• Yeast Quantity: Use a Starter, better, use a yeast cake. Per George Fix for an ale, you want to pitch around 0.75 million cells of viable yeast, for every milliliter of wort, for every degree Plato, lagers double that. Under pitching can result in “tired” yeast that is unable to finish the job. It is difficult to over-pitch a Big Beer.
• develops strong yeast during their growth phase allowing them to completely consume all the fermentable sugars. Oxygen is necessary for yeast to produce lipids which act as a growth factor in the growth stage of the fermentation and protect the yeast from alcohol toxicity near the end of the fermentation. Perform this step at the start and at 12-14 hours for very big beers.
• Yeast Nutrients: Now that we have oxygenated the yeast, does the yeast have everything they need to grow and multiply before they start fermentation and alcohol production? Adding yeast nutrients ensures that they do. This may be important, depending on wort composition, to maximize attenuation.

Fermentation

• Ferment Temp: We do not want to ferment at temperature that are optimum for the yeast, we want to ferment at temperatures that are optimum for the beer that we wish to produce. The yeast will be much “happier” at higher temperatures. Too low a temperature will cause the yeast to slow down, go dormant, flocculate out of solution. Near the end of fermentation the character of the beer, esters and phenolics that are characteristic of the beer will have been formed. We can raise the temperature of the wort toward the high end of the band. Danstar Nottingham is “rated” 57° to 70°F for beer production, we would raise the wort temp in this case to approach 70°F to help the yeast through the last few points.
• Ferment Time: A big beer will frequently, not always, drop its last few points over a period of months. That is why we will frequently say “when the beer is ready it will be done”. There are a lot of things that may hinder fermentation especially at the later stages of brewing a big beer. Many of these are issues are addressed here. All I can say is that when all else fails, be patient.
• Rouse the Yeast: Lets try to keep as much yeast in suspension as we can to ferment the remaining sugars, especially with highly flocculent yeast strains. Lacking continuous agitation I like to rouse my yeast 3 times a day. When I get up, when I come home from work, and when I go to bed.
• Supplemental Yeast: A way of restarting a stuck fermentation, or helping out a weakening one is to all an active starter of either the same strain or a different strain of yeast. Since we perform this step frequently when we perceive that the fermentation is in need of help, the alcohol levels are elevated, etc. and so on, we want to pitch active working healthy yeast. Resist the urge to mage the starter wort over 1.060 “so the yeast gets used to the high alcohol levels” because this will actually slow down and/or hurt the yeast culture. For the same reason I do not recommend directly pitching dry yeast. Carefully re-hydrate dry yeast and make a starter, pitch the starter at high krausen, the peak of activity, 12-18 hours after you make it.
• Beano: aka enzyme additions, the “ultimate” solution is to generally be avoided if at all possible. This product breaks down, and continues to break down complex, non-fermentable sugars in your wort into simple fermentable sugars thus increasing attenuation. There is no problem adding enzymes to your mash, just make sure you understand the results you get. But if you are trying to correct a situation such as you mashed too high and you discover this when fermentation stops well before you wanted it to and add it to your “Secondary”, the problem is stopping it. Nuff said!!

See Also

• Technical
• Alcohol By Weight
• Alcohol By Volume