View Full Version : Help calculate or estimate starting SG

JimSar

11-24-2009, 03:06 AM

This is an adaptation of STLBrewer's recipe for sweet mead. No water, just juice and honey, and no mixing of honey and juice, so not possible to do initial hydrometer reading.

Batch = 4 liters (green 4 liter jug, to be racked in regular 1 gal jug)

3 lbs clover honey (Central Valley, CA)

6 lbs 13 oz (by weight per digital scale) or 110 fl oz Trader Joe's Gala Apple unfiltered juice, no preservatives or additives, not even ascorbic acid.

7 g Lalvid D-47, rehydrated in ~100ml H2O at 104F, pitched at 70F. Must temp ~68F

1/4 tsp yeast nutrient, Oak Barrel Winecraft, generic(?) Fermaid K(?)

SG of unfiltered apple juice straight out of the bottle was 1.053.

It's been 7 hours since I pitched the yeast, it's now bubbling 1 per sec, almost consistently.

What's the calculated / estimated SG for this one? Thanks.

fatbloke

11-24-2009, 05:36 AM

This is an adaptation of STLBrewer's recipe for sweet mead. No water, just juice and honey, and no mixing of honey and juice, so not possible to do initial hydrometer reading.

Batch = 4 liters (green 4 liter jug, to be racked in regular 1 gal jug)

3 lbs clover honey (Central Valley, CA)

6 lbs 13 oz (by weight per digital scale) or 110 fl oz Trader Joe's Gala Apple unfiltered juice, no preservatives or additives, not even ascorbic acid.

7 g Lalvid D-47, rehydrated in ~100ml H2O at 104F, pitched at 70F. Must temp ~68F

1/4 tsp yeast nutrient, Oak Barrel Winecraft, generic(?) Fermaid K(?)

SG of unfiltered apple juice straight out of the bottle was 1.053.

It's been 7 hours since I pitched the yeast, it's now bubbling 1 per sec, almost consistently.

What's the calculated / estimated SG for this one? Thanks.

well whether you'll get any guidance from the mead calculator, I don't know.

the only true way of getting a starting gravity is to measure it yourself - hydrometers are reasonably inexpensive.

So far, the only figure you have is the 1053, but how did you get that ?

You'd really need to mix the batch and then measure - there's no real way of estimating, especially without a fixed datum for comparison, and even the the comparison would probably be so far out as to be useless.

Hell, you can have multiple batches of the same recipe and not only could they reflect different SG, but using the same yeast, they ferment at different speeds and the end result tastes different.

Sorry if that's not much help.....

regards

fatbloke

wayneb

11-24-2009, 11:02 AM

While it is possible to estimate the starting SG of a honey only must, once you've added fruit or fruit juices of any kind, all bets are off. There is too much variability in the SG of fruit juice (even the commercially produced ones) to do an effective calculation.

That said, if you have measured the gravity of the juice and you know it to be 1.053, we can do a quick estimation based on "average" water content honey. This also adds uncertainty to the estimation, so as fatbloke indicates, the best way to find your starting gravity is to measure it once the must is mixed. BTW, that is one of the most compelling arguments for mixing the honey thoroughly before starting fermentation, IMO.

The estimate uses the following equation:

S1*V1 + S2*V2 = St*Vt,

Where S1 is the specific gravity of the first ingredient (let's say the honey), V1 is its volume, S2 is the gravity of the apple juice and V2 is its volume, and St is the specific gravity of the total mixture, where Vt is its volume.

I've actually done this calculation for another member about a year or so ago (and in that earlier example I provided the "average" 17% moisture content honey SG) in a post to another thread, so in order to encourage use of our Gotmead Search Tool by all the members who might want to see this ;) I'm going to ask you to search for it. ;D

Now if you're not mathematically inclined, I'll be happy to work it through for your particular case. PM me and we'll take it from there! :)

JamesP

11-24-2009, 08:12 PM

Using the Mead Calculator (6.39% sugars in apple juice)

SG = 1.119 or around 16% Alc if ferments dry

(14% of Alc due to honey. If you have really sweet apples it would probably only boost it to 17% Alc)

JimSar

11-24-2009, 10:55 PM

Using the Mead Calculator (6.39% sugars in apple juice)

SG = 1.119 or around 16% Alc if ferments dry

(14% of Alc due to honey. If you have really sweet apples it would probably only boost it to 17% Alc)

Here's what I came up with, using Wayne B's formula: 1.1188

1.119 per Mead Calculator vs 1.1188, close enough for government work, eh?

The wildcard here, of course, is the moisture content of the honey. ASSume 17% gives you an SG of 1.4237.

1.4237 * 702.39 ml + 1.053 * 3253ml = 4425.40

4425.40 = St * 3955.39ml

St = 1.1188

Thanks, everyone, for your help. Please let me know if any of my calculations or assumptions are wrong.

I'm not sure about this line of thought: I came up with 702.39ml for 3 lbs of honey this way: 3#/2.2 = 1.3636kg. SG of H2O is 1.0, so, if it were H20, volume is 1,363ml. Since our honey has SG of 1.4237, the volume of 1.3636kg honey calculates to 702.39ml (unadjusted for temp). Am I off track?

BTW, PH of the must at pitching + 24 hours is 3.4 using a freshly calibrated PH meter. Stirred the honey off the bottom, and aerated with aquarium pump for a few minutes because the jug's neck has very small surface area exposed to air.

Jim

wayneb

11-24-2009, 11:27 PM

Jim, you nailed it! And you've also worked an independent verification of JamesP's mead calculator!! (Not that it hasn't been verified before, but now you personally can have a bit more confidence in it than if you were to have to trust it "blind.") ;D

JimSar

11-27-2009, 03:34 AM

Thanks again, now a question about sugar content of apples / apple juice, since I'm a bit confused here. The mead calculator shows 6.39% sugars. The nutrition label of the unsweetened, unfiltered 100% juice shows 28 grams of sugars per 240ml serving. That's approximately 11% after adjusting the serving weight for SG of unfiltered juice. Unadjusted it is 11.67%. What gives?

wayneb

11-27-2009, 02:44 PM

Apples contain a lot more than the juice; don't forget about the rest of the cell structure in the plant (cellulose, pectins, etc.) that get left behind when apples are pressed for juice. Since the sugars are water soluble, when you extract the juice from the rest of the apple most of the sugars come with it. Thus, the juice is a higher net percentage sugar than are the apples before processing.

akueck

11-28-2009, 02:53 AM

If you've ever eaten a pound of apple rings, you'd know that apples are pretty high in fiber. Mmm, fruit!

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