Declining Extract Efficiency at Higher Original Gravities

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A 15-gallon mash/lauter tun.

You will frequently hear homebrewers complain of losing extract efficiency when brewing higher gravity beers. The reason for this is not widely understood in homebrewing circles and not incorporated into recipe formulation software. A loss of extract efficiency at higher original gravities is not inevitable. When it occurs, it is the result of the techniques chosen by the brewer.  It is of particular relevance to brew-in-a-bag (BIAB) brewers, but affects any homebrewer who collects and boils the same amount of wort regardless of the size of his or her grain bill.  In this article, I’ll explain the problem and how to fix it. And tomorrow, I’ll show you one to account for it if you chose not to fix it.

Let’s start by stepping through the relevant portions of wort production when brewing a normal gravity beer (say, around OG 1.048, 12 ° Plato, for an alcohol content of approximately 5% ABV). Let’s say a brewer typically gets around 70% extract efficiency and so mashes around 9 lb. of grain for his 12 °Plato beer. (The exact numbers aren’t important, just the relative differences compared to later examples.) Let’s say he collects about 6 gallons of wort — for a pre-boil volume around 10 °Plato — and boils it down to 5 gallons to hit his target OG.

Now lets take a second example. This time the same brewer is trying to brew a barleywine. He wants the OG to be 22 °Plato, so he mashes 17 lb. of grain. At 70% extract efficiency — which he achieved with the 12 °Plato beer — he should hit this target. He collects 6 gallons of wort, boils it down to 5 gallons and . . . his OG is lower than expected. Why?

The reason his OG is lower is simple — he did not fully sparge the grain bed (as he did with the 12 °Plato beer). In the case of the 12 °Plato beer, his grain bed weighed 9 lb. and he collected 6 gallons of wort from it. In the case of the 22 °Plato beer, his grain bed weighed 17 lb. — nearly twice the weight as before — yet he only collected the same 6 gallons of wort from it. Had he collected an equivalent amount of wort per unit of grain, his efficiency would have been the same (assuming all other variables are equal.) Specifically, if he had collected a little over 11 gallons of wort and boiled it down to 5 gallons, his extract efficiency would not have suffered. In this case, the pre-boil gravity of his wort would have been around 10 °Plato. In the case in which he only collected 6 gallons, it would have been higher. However,  the total amount of sugar the brewer yielded would have been less because he left sugar behind by not fully sparging (rinsing) the grain bed.

Sometimes it is good to look at things from more than one angle, so here’s another way to visualize the problem. If you mash at the same thickness for every brew, but collect the same volume of wort (regardless of the weight of your grains), the volume of strike water goes up for bigger brews, but your volume of sparge water actually decreases. This is because — with larger mashes — you collect more first wort. As such, you need less sparged wort to hit the same kettle volume. But of course, less sparge water means the grain bed is not rinsed as thoroughly.

The solution to this problem is that the volume of your pre-boil wort should scale with the weight of your grain bed. If you have more malt in your mash tun, you’ll need correspondingly more strike water to mash with and also more sparge water to rinse the grain bed. If you collect the same amount of wort per unit of grain every time (and don’t oversparge), your pre-boil wort gravity will be the same for every brew (around 10–11 °Plato). You will then boil it down to the correct volume and gravity. When I brew, I find that my grain bed is fully sparged when I collect around 0.65 gallons per pound (5.8 L/kg) of grain. Your number might be different — depending on your crush and other variables — but that’s a good place to start. When the grain bed is fully sparged, the brewer has rinsed out all of the sugars possible before excess tannin extraction begins.

So, the solution to the problem is conceptually simple, but you can see why many homebrewers don’t scale up their pre-wort boil volume accordingly. In some cases, the limitations of their equipment won’t let them. In others, they wish to avoid the excessively long boil times associated with bigger beers and simply compensate by adding more grain or supplementing their wort with malt extract. Tomorrow, I’ll show you one way to anticipate the degree your extract efficiency will drop so you can compensate for it during recipe formulation.

 

Related Articles

Barleywine (All-Grain Wort Production)

Extract Efficiency Tradeoffs

Comments

  1. Reminds me of an old Don O. Youtube video!

    https://www.youtube.com/watch?v=94Oe-YZVbGg

  2. I find this discussion useful, as I am a BIABrewer who likes big beers, and this keeps biting me in the butt. It seems this is the real reason for partiglye brewing, as then you can make use of the extra sugars.

  3. Herb Meowing says:

    If a grain bed is fully fly-sparged when the pH hits 1.008 (IIRC) then when is a grain bed fully batched-sparged?

    • Chris Colby says:

      For fly sparging, a grain bed is fully sparged when the specific gravity of the final runnings drops to 1.008 or (as will happen at the same time, in most cases) the pH rises to 5.8. At this point, if you try to rinse out more sugars, you’ll get excess amounts of tannins along with them. For batch sparging, it’s when you hit the same wort-collected-to-grain-used ratio. For me, on my system,. it’s around 0.65 gallons of wort collected per pound of grain.

  4. Little Boy Brew says:

    Herb, it seems the logical answer would be to add enough water to the second batch sparge such that the gravity of the wort in the mash tun is 1.008. You may have to do a third batch sparge, depending on the size of the mash tun. Either way you will spend time and energy boiling that water away. I would rather calculate my expected efficiency before I mash and size the grain bill accordingly.

  5. Looking forward to the followup!! I think this is something a lot of brewers deal with, but don’t know how to properly account for.

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