heating the wort to boil takes long time

I have a question about the time which is reasonable to bring the wort to a boil after mash.

Last two batches I have had 23 litres of wort before the boil and taking this amount of wort to boil takes 40 minutes with my equipment. Does anyone know if such a long period will have effect on the taste of beer or it does not matter? I am using a brewbag and the malt has been removed before cranking up the burner.

Both of these beers have turned out really malty and even with an off taste after 2 weeks of sitting in the fermenter. The mash schedule was 65C for 60 min and 75C for 10min both times. First batch was sitting in the fermenter for almost 4 weeks and then it got better.

Before that I did couple of batches where I had only 15l of wort to boil and the mash schedule was 40C -10min; 62C -40min; 70C - 10min and this beer tasted good already after priamary fermentation - with no off taste what so ever.

Was I mashing with too high temperature or is it crucial to keep the time for bringing the wort to a boil as minimal as possible?

Thank You!

Your mash temps seem ok, not knowing what you're brewing. When I drain off my first runnings I immediately put some heat to it while waiting on the sparge water. Once I start to drain my sparge water into my BK I turn the heat up.
It usually takes me 15 min or less to get to a boil.

The time to boil is not really an issue. It's mostly inconvenient. However, if you have a hard time maintaining a rolling boil, then this can have an impact. The actual churning of the boil does lots of things - namely the isomerization of the alpha acids in the hops (bitterness). If you can get to a boil and then maintain it at a good rolling state, I think you are fine. In any event, if you think it's taking too long, just add more BTU's in the form of a bigger burner or more watts to your element, whichever you happen to be using.

If you are finding your beer to be too malty then you need to evaluate both your ingredients as well as your thermometer. Many thermometers are not accurate and people can typically be mashing higher or lower than they think they are and a few degrees in one direction can make a big difference.

With recipes you need to look at the percentages of the less fermentable types of grains you are using, for example, if your crystal or darker grain content is too high you can develop a less fermentable wort leading to a maltier finish in the final product with more body and mouthfeel. If this is then coupled with too high a mash temp it can make matters worse if that's not the type of finish you were looking for.

as for the boiling questions, time to bring to a boil is really not an issue but as mentioned you need more BTUs if you want to shorten the amount of time needed.

Thanks for You answers.

The percentage of the crystal malts was indeed way overshot with the first batch, but for the second one I kept it below 7% which should be fine, but still it was quite malty and had an off taste. Now the second batch has been sitting in fermentor for 2 weeks. Yesterday I took a sample and it has gotten better when I last tried it, but still has an off taste and neither me nor my friend could define the taste. Gravity has not changed from a week ago - It is 1012 OG was 1046.

I will check my thermometer, lower the mash temp as I am aiming for medium- low bodied beer and I will not add any water before boiling the wort to be 100% sure that the boil is ok. Hopefully all these aspects will get me where I am aiming.

Tasting after 2 weeks in the fermenter is tasting young green beer. If you let that sit another week, then bottle age for 3 weeks minimum you'll have a much different beer than what you're tasting now.

Check your thermometer. If 62C gave you a profile you liked but 65C gave you too malty a profile, I would suspect the thermometer.

In theory, your 75C should have halted all conversion of starch to sugar. Did you do an iodine test? If your thermometer is reading low, you could have deactivated the enzymes before they had a chance to finish converting.

I know that 2 week is a bit too soon, but batches before the final two tasted good already after one week in primary. So that got me thinking, what did I do wrong the last two times. One more thing - before I used Safale US-05, but for the last two ones I used S-04. They both fermented quickly, that's why I didn't think that the yeast made this difference.

I will definately check my thermometer and just to be sure I will make less wort to boil.

That's a whole new variable with the yeast. Anything else you didn't mention such as your fermentation temperatures were different with the last batch or your fermentation temperature is outside the range for S-04?

Here are the spec sheets for those two yeasts. According to the manufacturer, the S-04 has a lower attenuation/more residual sugar than the US-05.
http://www.fermentis.com/wp-content/uploads/2012/02/SFA_S04.pdf
http://www.fermentis.com/wp-content/uploads/2012/02/SFA_US05.pdf

When you introduce multiple changes, it is really hard to pinpoint which change caused a specific effect.

The temperatures have been 21-22C with all batches. With exception for first two batches, where at the beginning of fermentation the temp got up to 26C. The US-05 started fermenting really violently, but the temp went down to 22C with half a day or so.

I admit that for beeing such a newbie at brewing, I took quite a risk changing so many variables after I successfully made only 2 batches. Think I'll go back to the recipe that worked and start changing things one-by-one.

Thank You anyway for all Your help and suggestions.