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When to measure OG

Please help settle a debate; Do you measure OG before or after pitching, and why?

Before

Well, that’s what I do; but only because it’s what I was taught. Without the why, it doesn’t help settle the debate.

If you measure after pitching, you’ll get a higher number, as the yeast in suspension contribute to the measurement. But, the argument goes, if you want your measurements to reflect the internal changes of the solution, you shouldn’t add anything to the solution after the baseline is taken. I can’t argue that logic, and have no counter argument.

I’m under the impression the whole purpose is to measure how much sugars were converted to alcohol. In that sense, the yeast isn’t converting itself to alcohol so shouldn’t be considered in terms of the OG.

Well, that’s what I do; but only because it’s what I was taught. Without the why, it doesn’t help settle the debate.

If you measure after pitching, you’ll get a higher number, as the yeast in suspension contribute to the measurement. But, the argument goes, if you want your measurements to reflect the internal changes of the solution, you shouldn’t add anything to the solution after the baseline is taken. I can’t argue that logic, and have no counter argument.[/quote]

If the yeast is in suspension, not dissolved into the liquid, it will not change the reading. Even if it did, so little volume (assuming decanting) will have a negligible effect. In short, it just doesn’t matter if you measure before or after pitching.

Shouldn’t OG be checked before aeration? I would think that aeration would affect the reading and I always aerate before pitching.

Aeration will not affect the reading. Why would it? It doesn’t change the amount of sugar dissolved in the wort.

I do it before to avoid sampling out yeast even if its a tiny bit.

After aerating, it is sometimes a little more difficult to get a good wort sample through the foam, but otherwise, it should have no effect…I use a refractometer, though, so it’s easy to take a couple quick readings in any event

It makes no difference when you check the OG as long as:

  1. The wort is cool or you adjust the reading for temperature.

  2. Fermentation has not yet begun in earnest. For example, if you forget to check the gravity until the next day after you pitched but there isn’t a krausen yet, it might screw up the reading anyway because the beginning of fermentation is invisible. But if you check gravity within like an hour or two you’ll be fine.

Follow those two rules, and nothing else matters. Oxygenation, pitching yeast, not pitching yeast… no big deal. Just do it all at approximately the same time.

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