Lactose how much is too much?

So I have never used lactose before and i was wondering, really, how much is too much?
My plan is to use it in a milk stout and since the idea i have is a little off the wall im thinking of only doing a one to two gallon batch.
I read an article a little whiles ago that a good rule of thumb is one pound for every 2 gallons however, a lot of receipes i have seen only ask for a pound. I guess I would like input from other people that have used it.

How much can I use before it starts to ruin the beer?

one pound for every two gallons will completely ruin your beer.

From what I found when researching the style was the average was a pound per 5 gallons. So I found a solid left hand milk stout clone, made a few adjustments and brewed it. I added a pound of lactose during the last 10 minutes of the boil. The beer turned out way too sweet and the mouthfeel was a little funky. If I were to brew it again I would cut the lactose in half. Taste it before bottling then and only if needed add no more than an additional quarter pound to my 5 gallon batch.

If you are only doing a 1 gallon batch I would keep it to 1.75oz. then taste it before bottling. You can always add another half ounce at bottling if you want it to be a bit sweeter.

Make a two gallon batch and split it. Add 1.5 oz to one gallon and 3 to the other. Bottle and compare. Personally, I find 8 oz in five gallons plenty.

I've used .5lb, .75lb, and a full 1.0lb in 5 gallons. 1/2 lb was not enough for me, but was noticeable. .75 was better. glad I upped the hops a bit (extra .5oz of fuggles at 60 min) with 1lb in a 5gallon batch. I wouldn't go over 1lb per 5 gallons... and I love milk stouts! 1/2 to 3/4lb is the best range.

david_42 said:

Make a two gallon batch and split it. Add 1.5 oz to one gallon and 3 to the other. Bottle and compare. Personally, I find 8 oz in five gallons plenty.

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+1. I recently used 4 oz in a 2.5 gallon batch of sweet stout. It placed 2nd in a local comp. with a good score and my buddies and I liked it, but the BJCP judge found the sweetness to be overpowering and really he's right. I liked the sweetness with the chocolate but it's not exactly a perfectly balanced beer.

starrfish said:

I've used .5lb, .75lb, and a full 1.0lb in 5 gallons. 1/2 lb was not enough for me, but was noticeable. .75 was better. glad I upped the hops a bit (extra .5oz of fuggles at 60 min) with 1lb in a 5gallon batch. I wouldn't go over 1lb per 5 gallons... and I love milk stouts! 1/2 to 3/4lb is the best range.

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I tried 8oz and then another batch with 1 lb and that is slightly too much. I agree with starfish 1/2-3/4 lb is about right for a 5 gallon batch.