Question about O.G & S.G

[Pwntang]

Hi all,

I have some questions about gravity and fermentation and would really appreciate any advice.

Am I right in saying that there is a simple concept that the larger the difference between the OG and FG the higher the alcohol content?

Can you control how low the gravity goes during the fermentation process? If you wanted to make a sweet brew, for example, you would want a slightly higher gravity? Would you use non-fermentable sugars or something?

Does more yeast equal more sugars are converted into alcohol?

I really want to understand whether you can control the gravity in some way and if so how you would go about it. Right now I'm very un-scientific and basically measure the O.G then add yeast and wait to see what it goes down to (in other words, I put the yeast in and simply hope for the best!).

It would be great to be able to estimate how it will turn out before it's ready to drink so that I can plan brews of a certain strength / taste.

Thank you in advance to anyone who replies!

 

[kanzimonson]

Great questions - these are some of the most important things to understand in brewing.

You are correct that the higher the OG, the higher the alcohol in your final beer. That's just simple math - the more sugars that are available, the more alcohol the yeast will produce.

You can control the FG of a brew in a sense but I suspect not in the ways you are thinking. In any situation, the question is "how much fermentable sugar is there in this wort?"

There are many different types of sugars, and some of them cannot be fermented by yeast. Some of those sugars are perceivable by the human tongue as sweet, while some are flavorless. Still, if you put a bunch of flavorless, unfermentable sugars in water, your tongue would probably perceive that "there's something in there." It would probably taste thicker.

Also, each yeast strain has evolved to a point where it can only ferment a certain percentage of the sugars in a wort. Compare English ale yeast to American ale - the American ale can consume more sugar types than the English, and therefore beers made with this yeast will have a lower FG.

Also, mash temperatures affect the types of sugars in your wort. The higher the mash temps, the more long-chained sugars you are left with (multiple carbon atoms linked together in a long chain). The yeast can't ferment a lot of these. Lower mash temps favors certain enzymes that break down the starches into more fermentable sugars.

Also, yeast health and pitch rate will affect how much sugar is consumed. The healthier the yeast, the more likely they are to continue fermenting. If you don't pitch enough, you might have an underattenuated beer. But it's not like if you pitch 10 times the recommended amount you'll ferment all the sugars - there are limits here.

I could go on and on with this topic but I'll stop the response here for now.

 

[Homercidal]

OG is the ratio of water to sugar in the wort.

You can control how much of this sugar gets converted by several methods, by mashing higher in temp (makes more sugar that is not as fermentable) or by using yeast that quit before as much sugar is fermented. Or you can add unfermentable sugar with additions like crystal malts etc.

Or you can kill the yeast before they finish their job. I think Campden tablets will do this, as will high heat.

The killing of the yeast is the least preferable to the purists. I would look at the descriptions of various malts and read up on recipes that indicate that they are maltier, or sweeter. This may give you a clue as to what malts and what percentage of those malts will make a sweeter beer.

Another method is to limit the amount of bittering hops used, which will make a beer taste sweeter due to the lack of bittering.

I must add that a sweet beer might sound tasty but they rarely end up as good as people think.

 

[kanzimonson]

One thing that should be clear: just because one beer has a higher FG than another beer, that does not automatically mean the first beer is sweeter... there are many factors that contribute to sweetness.

 

[GilaMinumBeer]

Yes

Yes

Partially.

The ultimate way to control the final outcome of any beer is to go all grain and control fermentability by means of mash temp management.

 

[Pwntang]

Thanks for your replies! Some good information and knowledge here.

There are many different types of sugars, and some of them cannot be fermented by yeast. Some of those sugars are perceivable by the human tongue as sweet, while some are flavorless. Still, if you put a bunch of flavorless, unfermentable sugars in water, your tongue would probably perceive that "there's something in there." It would probably taste thicker.

I've read somewhere that Honey is a good option as not all of the sugars are fermentable. Is that right?

Also, mash temperatures affect the types of sugars in your wort. The higher the mash temps, the more long-chained sugars you are left with (multiple carbon atoms linked together in a long chain). The yeast can't ferment a lot of these. Lower mash temps favors certain enzymes that break down the starches into more fermentable sugars.

Interesting. I did not know this. I mashed my last brew at 65c.

 

[kanzimonson]

Actually, honey is practically 100% fermentable. Do not ever add honey to a beer thinking it will make it taste sweeter. The yeast will eat the sugars and all that honey sweetness will be gone. HOWEVER, what you will be left with is the aromatic and flavor compounds in honey, and these sorta trick your brain into thinking it's tasting something sweet.

Still, the amounts of honey we use in beer are very diluted, so I don't think the cost of honey is worth it. I'd rather caramelize some granulated sugar.