A friend of mine just set a Morgans Golden Saaz Pilsner with kit yeast and 1kg DME + 1kg sugar. He is fermenting at ~23°C.
The kit requests for 1 kg of sugar but my firend accidentally put much more.
What would be the effect of this extra sugar. Will it spoil the taste of the kit?
More sugar means more alcohol. One kg of DME and 1kg of sugar added to a Morgan's kit should push your ABV up into the 5.something percent range which is a bit oomphy for a Pilsener but still acceptable.
However, more refined sugar (corn sugar, table sugar, etc.) also means that the yeast might become stressed (especially due to high levels of table sugar, i.e. sucrose) and may produce off-flavours, most noticeably green-tasting acetaldehyde (green apples flavors, freshly stripped tree bark aroma's).
Also keep in mind that if the yeast has to deal with high levels of refined sugars, it may loose its ability to ferment malt sugars, which may lead to a stuck fermentation.
Having said that, once the beer is in the fermenter it's a bit late to take ingredients out of it, so I suggest you let it ferment, bottle, and see what comes out of it. You'll probably be fine. Slight off flavors can usually be removed by more bottle conditioning.
Because alcohol tastes sweet, the extra alcohol will affect the flavor of the beer. The balance of hop bitterness and sweetness will be affected. The beer might also seem drier. Simple sugar ferments our pretty well, so expect a thinner bodied beer as well.
And if you like the resulting beer, none of the above matters much.
I'll try to keep this simple and not get into the chemistry of it all, more sugar means more food for the yeast equals more alcohol in the final beer. Yes changing the alcohol content of a beer does change the overall taste. Usually it will smooth out the finish. But more important than the quantity of alcohol, the type of sugar used in the creation of the alcohol determines the type of alcohol and affects the flavor even more that just changing the quantity.
For example the alcohol created by adding more DME (also a sugar) will taste different in the final beer than the alcohol created by adding more sugar (I'm assuming you added either cane or beet sugar). Sometimes with added "table" sugar it can make your beer taste more like apple cider.
Finish it and give it a taste. That is the only real way to know for sure. If it is undrinkable at least you will have something to feed to your garden. I've had a few of those myself. Good luck and cheers!
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