Gravity and Lactose

[Payson]

Here's a question concerning gravity and lactose:
Does lactose artificially raise the OG or give a non realistic reading due to its non-fermentability? What about generous use of dextrine malt, or in my case, both? If so, how would you convert to a more useable number?

[HogieWan]

Any soids you add will raise the gravity. Some of those solids will be converted to alcohol which is lighter than water. lactose won't "artificially" raise the gravity - it will truly raise it. It will just stay there and leave your FG higher.

[Payson]

So, if a beer has an OG of 1.050, generally speaking, the alcohol will be 5% (ballpark). However, with lactose and a generous helping of dextrine malt, if the OG is 1.050 then it's a safe bet that the ABV will be less than the preceeding example? I think this stands to reason??? :confused: The beer that brought the question to mind had an OG of 1.090 which is higher than I anticipated, now I'm wondering in advance what type of alcohol content it'll have. I'm guessing it'll be virtually impossible to tell until the time for FG arrives.

[brewmonkey]

A beer with a 1.050 gravity has the POTENTIAL to have X% alcohol. As you are thinking if you have a certain percentage of non-fermentables in solution you will obviously have a lower alcohol percentage at the end of fermentation.

[HogieWan]

What he ^ said

OG doesn't matter - it's the DIFFERENCE between OG and FG that matters

[Payson]

I understand that it's the difference that matters but there seems to undeniably be a link between OG and ABV. In other words, most beers with an OG of 1.050 will have an ABV of 5.0% (give or take) Likewise, an OG of 1.075 will be roughly 7.5% ABV. I guess what I'm saying is that by looking just at OG, you can pretty accurately guestimate the ABV based soley on the last two numbers. Simplistic but it seems to basically work out. The sweet stout I'm making will not follow this same pattern though. It doesn't create a problem for me, I've just never thought about the fact that it (OG) could be altered to the point that what I thought was a simple, quick starting point is totally off in this case. Interesting!

[HogieWan]

With a high OG, most of the sugars are fermentable and will create alcohol. But as you up the fermentable and non fermentable sugors, the FG will remain close to the same. The more alcohol present, the lower the FG (alcohol is lighter than water and will ofset the gravity of unfermentable left in the beer).

[brewmonkey]

Originally posted by Payson
I understand that it's the difference that matters but there seems to undeniably be a link between OG and ABV. In other words, most beers with an OG of 1.050 will have an ABV of 5.0% (give or take) Likewise, an OG of 1.075 will be roughly 7.5% ABV. I guess what I'm saying is that by looking just at OG, you can pretty accurately guestimate the ABV based soley on the last two numbers. Simplistic but it seems to basically work out. The sweet stout I'm making will not follow this same pattern though. It doesn't create a problem for me, I've just never thought about the fact that it (OG) could be altered to the point that what I thought was a simple, quick starting point is totally off in this case. Interesting!

Yes & No(mostly no), you cannot look at the OG and determine alcohol. Like I siad, it determines potential alcohol.

I understand what you are saying but it just does not work that way. In addition to the unfermentable properties of wort you also have yeast issues to deal with. The yeast brewers use will not ferment out 100% (for the most part, there might be 1 or 2 strains that will) so you have to deal with that as well.

So you cannot just look at the OG and say it will have X% alcohol. In fact a beer with a 1.050 OG would more likely be closer to 4% abw then 5% abw, a good 20% difference.

Remember to determine alcohol by weight you take subtract the finishing (terminal) gravity from the starting gravity and then multiply by 105. That number is your abw%. If you multiply the abw% by 1.25 you have a rough estimate of the abv%.

To many factors involved in the determination of the final alcohol content to simply look at the hydrometer and say "it will be this % abw."

[stronk]

In addition, I always find that thicker, darker beers (like a stout) will tend to have a relatively high OG and high FG. I guess various things contribute to that.

[HogieWan]

Originally posted by stronk
In addition, I always find that thicker, darker beers (like a stout) will tend to have a relatively high OG and high FG. I guess various things contribute to that.

Ethyl alcohol and water are thin and clear, so anything that adds body and color are disolved solids that will add density. That density will naturally affect the SG and FG