You’re talking about rehydrating dry brewer’s yeast. So yes, if you’re using dry yeast it is recommended by many experienced homebrewers to “proof” the yeast before adding it to the cooled wort.

Just proofing (or soaking, as you mentioned) the yeast in warm water, like you might do if your making homemade pizza dough or something, is a little better than just pitching dry because it prepares the yeast.

If you’re using liquid yeast you definitely DO NOT want to proof it. Liquid yeast is prepared so you can just shake it up and stir it into the fermenter.

Another, and some may say better, option is to make a “starter.” I do it everytime, and it helps to acheive a quicker onset of fermentation in many cases, and also increases your chance of having a more complete fermentation with the desired, expected result.

For example, if you brew a recipe that is supposed to result in an ABV of about 6%, then you’ll improve your chances of seeing that result if you use a starter.

To prepare a starter you would dissolve some malt extract in hot water, let the water cool, trasfer it to a small jar, like a 1/2 gallon growler, pitch the yeast, swirl it up to mix it, and pop a stopper and an airlock on it. It is recommended to do this at least 6 or 12 hours before you brew. I do mine the day before.

In that case you basically have a little batch of beer fermenting, allowing the yeast to proliferate. You then stir that fermenting starter into your cooled wort in your large fermenter. You will see a more complete fermentation using a starter. Thanks for asking, because now I’m going to write a nice little blog post on how to prepare a yeast starter, and the benefits of doing that.

Using malt extract instead of the provided “booster” for the beer will result in a thicker beer, and potentially sweeter, depending on the malt extract you use. The sugar “booster” is an adjunct used to boost the alcohol level without altering the desired flavor and body of the beer based on the recipe.

If you substitute malt extract it won’t hurt the beer, but it can potentially thicken the beer and throw off the flavor a bit from what was originally intended. If you want to taste what Mr. Beer had in mind for the recipe, then use the booseter.

But of course, homebrewing is about experimentation, right?

I’m sure just adding an extra can of extract couldn’t hurt, but remember, you aren’t just increasing the sugars, if you use a second hopped extract you’ll also be boosting the hops characteristics, and that could make the beer too bitter. Using alternate yeasts with Mr. Beer ingredients can pose a problem if you use a yeast that is not matched with the style originally intended. But there is one other thing that can happen when you start mixing up yeasts, adding sugars, or even using yeast starters to improve fermentation. You run the risk of blow-off (the result of a very active fermentation during which the foam and preasure increase and escape the airlock), which would create a rather nasty mess if steps aren’t taken to contain the situation before hand.

Plus, if the lid on the Mr. Beer fermenter clogs due to blow-off it could skyrocket into your ceiling, spewing shmutz all over the place, I’ve had it happen. The fermenting beer will be exposed to potential contamination if you have to open it to clear the blockage, or if it blows its lid and sits for awhile.

So, if you want to boost the ABV and experiment on your own proceed with caution and do your homework. I would recommend trying one of the higher ABV beer kits first. In fact I think I’ll be picking up an Old Uncle Arnold refill pack to try out as I continue to put my Mr. Beer kit to the test.