Ok… Last week I brewed a 5 gal. batch and went over the “target” O.G. by 10 points (at the 5 gallon volume). For that batch, I just went ahead and pitched the yeast, and then had a discussion on here about the changes I might see as a result.
So… On my latest batch (Selair/PaulK 2007 Hefe recipe), I was again over the “target” O.G. at the 5 gallon mark. So on this one, I diluted it down to 6 gallons to hit the “target” O.G.
Any issue with doing that? I did NOT use a yeast starter – I just pitched the WL liquid yeast.
Only issue is that you are diluting out the bitterness as well as the sugar, and so the ratio of the two will no longer be as designed in the recipe. The flip of the issue you had on the last brew. Yeast starter is almost always recommended. Underpitching this beer might result in higher levels of phenols (clove), which I know some people do intentionally. So maybe an issue, maybe not. You’ll find out when you drink the beer.
It sounds like you should be starting to get a bead on your system efficiency, and you should start scaling your grain bill to reflect that. Most brewing software makes that modification easy; make use of it and hit target on future brews.
Two major factors associated with hitting your OG:
Volume measurements. If you don’t know exactly what your volume is at the end of the boil, then your OG will be as random as the waves crashing on the beach.
If you are an all-grain or partial-mash brewer, then the crush of the grains makes a huge difference. It’s possible to crush the grains TOO hard, which increases your OG. Most people don’t have this problem (although I did), for most people they’re not crushing hard enough and need to close the gap on their grain mill.
And then there is also the following which might make sense to advanced brewers only:
Another huge thing with all-grain brewing is that if you always sparge to hit exactly the same pre-boil volume (e.g., for 5.5 gallons you always start with 7 gallons before the boil, then boil off about a gallon, and lose another half gallon to hop material or whatever to end up with your 5.5 gal), then: The higher your intended OG, the lower your extract efficiency will be. And the opposite is true as well. If you want to hit your OG right on every time, then you need to understand how the amount of grist has an effect on efficiency, and thus need to account for slightly different efficiency with every batch. For example, if your average OG is 1.055 but then you want to make a 1.040 beer, your efficiency will skyrocket, maybe even into the 90% range. But if your average OG is 1.055 but then you want to make a 1.090 beer, then unless you do something to rinse more sugars and boil longer, your efficiency is going to suck, probably way down into the 50s. It’s just a matter of physics. If you want to improve or reduce efficiency, then you need to either modify your crush or you need to sparge more or less and boil longer or shorter.
For all-grain brewers who like to sparge to hit exactly the same pre-boil volume every time, there is fortunately a relationship between OG and efficiency that works pretty well. It is this:
GU + Efficiency = constant
So if your average OG is 1.055 and your average efficiency is 75%, then you can add these to get your own personal “constant”, which in this case would be 55 + 75 = 130.
So then taking that constant of 130, I know that if the same brewer wants to make a 1.040 with exactly the same process and pre-boil volume, his efficiency will be about 130 - 40 = 90%. And ditto for the 1.090 beer, it will be around 130 - 90 = 40%. In reality I have never experienced efficiency lower than about 52%, so the constant is not exactly constant for high gravity beers, i.e., there is a limit for the high gravity beers… but you get the idea.
I don’t mean to be an advertisement, but the gravity versus efficiency issue was just discussed on a recent Basic Brewing Radio podcast. Dave’s math is easier, but it was a good discussion.
If you are using all grain kits you will have to try and match your efficiency to that in the recipe. Or use a brewing software to adjust the recipes to your efficiency and order your own ingredients.
Rebuilt… Dang it!!! I didn’t even think about the bitterness dilution! Son-of-a…
Thanks, everybody, for the other comments! I’ll try to find that PodCast. Seems I am constantly between 10 and 20 points over the target O.G., so I should probably start playing around with making some adjustments.
