Started out with 3 gallons in my pre-boil and then it reduced to 2.25 gallons after my 60minute boil. Great...then after letting it cool and transferring it to the fermenter, I added the extra 3gallons of water and took my gravity reading. Somehow, the OG came up at. 1.017...WAY too low and definitely not what BeerSmith gave me as the OG I should have.
Something seems very odd about the numbers here. I could be mistaken and don't take this the wrong way but I'm not sure it is even possible to miss an OG for a extract/partial mash batch by nearly 42 gravity points. I think your gravity is actually much higher than 1.017. With 8# of liquid extract in a 5 gallon batch I roughly get a 1.057 starting gravity. If you were to have only used the 2# of amber extract you would be at 1.014. So really I can't think of any reason why that 6 pounds of extract sugar would have disappeared during the mix. Unless you had a crazy wild yeast take over during the boil or you spilled a TON of LME on the stove, your sugars should be in there. Gently swirl your carboy again to mix everything up and take another sample.
1. The only things I can think of would be that the extract and the water didn't mix well enough during the boil and all the extract settled out at the bottom and became sludge.
2. A large portion of the clean fermentable wort was mistaken as trub and not poured into the fermenter
3. After adding 3 gallons of water in the fermenter, the wort sample you took the reading from didn't have an even mixture of wort. i.e. it was mostly water and a little bit of wort thus giving you an inaccurate representation of your wort's sugar composition.
4. Your hydrometer sample was too warm when you checked your gravity
5. You forgot to add your liquid wheat extract