How to measure beginning specific gravity in wine-making?

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cottonwoodks

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I know how to do this making cider, because it's juice, but how do you measure the specific gravity with all the fruit mashed in your initial fermentation vessel, so you can estimate the final alcohol level? By the time you discard all that pulp, a fair amount of fermentation has already taken place.
 

Mallerstang

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You can't! Measure specific gravity at the beginning when most of the juice is still in the fruit, that is. And of course if you leave a mesh bag of fruit in the fermenting must for several days, then squeeze out the juice when it's easy to do, which is my method, any measurement taken then will be meaningless.

So... I've found it helpful to start with a recipe that gives amounts of fruit, sugar and water to produce an end result of x%. There are formulas available that you can use to adjust the sugar amount to get a different strength wine.

Alternatively you can calculate starting water amount (if using any) and starting juice amount, look up sg of the fruit juice, do a weighted average, then calculate how much sugar to add for your desired starting sg. If you plan on squeezing the heck out of the fruit, expect the pulp to be 15-25% by weight of what you started with. Blueberries have lots of pulp, peaches less.

Take lots of notes for future reference!
 
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cottonwoodks

cottonwoodks

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You can't! Measure specific gravity at the beginning when most of the juice is still in the fruit, that is. And of course if you leave a mesh bag of fruit in the fermenting must for several days, then squeeze out the juice when it's easy to do, which is my method, any measurement taken then will be meaningless.

So... I've found it helpful to start with a recipe that gives amounts of fruit, sugar and water to produce an end result of x%. There are formulas available that you can use to adjust the sugar amount to get a different strength wine.

Alternatively you can calculate starting water amount (if using any) and starting juice amount, look up sg of the fruit juice, do a weighted average, then calculate how much sugar to add for your desired starting sg. If you plan on squeezing the heck out of the fruit, expect the pulp to be 15-25% by weight of what you started with. Blueberries have lots of pulp, peaches less.

Take lots of notes for future reference!
Alas. I was hoping there was something I was missing..... Thanks for your reply.
 

bernardsmith

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Actually, you CAN measure the nominal SG even in the grape. But you need to use a refractometer which uses not the density of the must but the angle at which light is bent (refracted) when it passes through water. Fruit juice is essentially water + sugars and the sugars dissolved in the water causes the light to refract at a different angle than it would if it simply passed through pure water. The more sugars in the water the more different the angle of refraction is. A refractometer is often used by grape growers to determine the ripeness of their grapes and all it takes is a drop of juice. Literally, one drop. BUT
If you only have an hydrometer you can still use that. Before you pitch your yeast you will have crushed some or all of your grapes and that crushing will result in a very small volume of juice. If you also add enzymes to help break up the fruit you will have a little more juice and there will be enough juice to collect and fill your measuring cylinder into which you place your hydrometer.
A third method but this is one based more on trust is that the vineyard , if reputable, will likely have measured the Brix of their grapes before harvesting (see paragraph 1 above). When you buy grapes from them they should give you data sheets for the grapes. Brix , pH, etc. (Multiply Brix by 4 to get an approximate SG ; Brix being the percentage of sugar in the juice - a Brix of 25 means that 25% of the juice is sugar.).
 
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